Improving Forage Quality from Permanent Grasslands to Enhance Ruminant Productivity

Abstract

Permanent grasslands play a crucial role in ruminant nutrition, providing cost-effective and nutritionally rich forage. Their effective management is essential for improving agricultural productivity and sustainability. This review examines factors affecting forage quality, including environmental conditions, botanical composition, conservation methods, and fertilization strategies. The impact of grassland management practices, such as cutting frequency, grazing systems, and soil fertility enhancement, on forage nutritional value is discussed. Advances in breeding, including genomic selection and molecular techniques, offer opportunities to improve digestibility and resistance to environmental stress. Furthermore, conservation methods, including haymaking and silage production, significantly influence forage quality. Special attention is given to the role of legumes and multi-species swards in enhancing protein content and mineral composition. The review highlights that optimizing forage quality requires an integrated approach, combining agronomic practices, genetic improvements, and sustainable management strategies. Future research should focus on developing resilient forage systems that maintain high nutritional value while adapting to changing climatic conditions.

1. Introduction

Grasslands are a fundamental component of temperate landscapes in Europe, playing a crucial role in the economically significant sector of animal production [1]. They are defined as lands used to cultivate herbaceous forage species, either naturally or under managed conditions, that have not been included in crop rotation for at least five years [2]. In Europe, grasslands account for nearly 38% of agricultural land [3] and globally cover 67% of all cultivated land [4]. In many regions, they dominate land use patterns.

Grasslands in Central Europe can be categorised by their origins into three main types: natural grasslands shaped by environmental factors and wild herbivores; semi-natural grasslands, developed through centuries of human activity since the Mesolithic-Neolithic transition; and improved (intensive) grasslands, resulting from modern agricultural practices involving highly productive forage grasses and legumes [5]. Beyond their agricultural importance, grasslands also prevent soil erosion and enhance biodiversity and ecosystem services [6,7]. Often unsuitable for arable crop production, they have historically been a primary forage source for ruminant livestock [8].

Grasses remain one of the most cost-effective and nutritionally valuable forage sources for dairy and beef systems [9,10], and their global significance is equally notable. Forage from grasslands is the most widely consumed livestock feed worldwide. In 2000, 2.3 Gt of forage were consumed by livestock, accounting 48% of all biomass used in livestock production, including 1.1 Gt in mixed systems and 0.6 Gt in grazing-only systems [4]. Grazing, a cornerstone of pastoral farming, not only sustains animal nutrition but also significantly influences ecosystem properties and functions. Herbivores optimise nutrient intake by selectively consuming plants and avoiding harmful phytochemicals [11].

Livestock plays a pivotal role in global food systems, contributing 40% of global agricultural GDP and supporting the livelihoods of at least 600 million of the world’s poorest people. Livestock products supply one-third of humanity’s protein intake, addressing undernutrition in some regions while contributing to obesity in others [12]. Ruminants, including cattle, sheep, and goats, efficiently utilise fibrous feeds from permanent grasslands to produce high-quality milk and meat, making these ecosystems vital to global food supplies [13,14].

Challenges such as climate change and geopolitical crises, including the invasion of Ukraine, have heightened the demand for increased food production across Europe. Improving forage quality is essential to enhance the nutritional value of biomass and ensure its optimal use as high-quality feed for ruminants. This requires a systematic approach to managing plant composition, growth conditions, and soil fertility, ensuring that grasslands fully realise their potential.

Enhancing forage quality involves selecting high-nutritional-value plant species, adjusting harvest timing, and regulating fertilisation and water availability. Maintaining species diversity also influences forage composition and nutritional value [15,16]. Avoiding soil degradation is critical, as it directly affects plant growth and levels of essential nutrients in forage [17]. Recent studies indicate that increasing plant diversity and adopting advanced fertilisation strategies can significantly improve forage quality [18,19].

In summary, permanent grasslands hold significant potential as a source of high-quality forage for ruminants. Their effective management can enhance agricultural productivity and sustainability. This review focuses on permanent grasslands located in the temperate climate zone, particularly in Europe, where both grazing and mechanical harvesting (for hay or silage) are common forms of utilization. Forage species and quality management practices discussed herein refer exclusively to grasslands, excluding annual forage crops grown on arable land. Therefore, this review aims to present the latest methods and findings related to improving forage quality from permanent grasslands and their impact on ruminant productivity. Both agronomic and breeding methods will be explored, alongside an analysis of the economic and ecological dimensions of forage quality enhancement, providing a comprehensive understanding of the benefits and challenges associated with this process.

2. Materials and Methods

In this scientific review, a comprehensive examination of existing research on the improvement of forage quality from permanent grasslands has been conducted. A systematic approach was employed to identify and select relevant studies published in peer-reviewed journals and scientific proceedings. The studies included in this review were selected based on specific criteria such as relevance to the topic, methodological quality, and the type of research (including experimental studies, field trials, and meta-analyses). The literature search for this review was conducted via the platforms Scopus (Elsevier, Amsterdam, The Netherlands; https://www.scopus.com), Web of Science (Clarivate, Philadelphia, PA, USA; https://www.webofscience.com), and Google Scholar (Google LLC, Mountain View, CA, USA; https://scholar.google.de). Access to these databases was from November 2024 to June 2025. The following keywords were searched for: plant factors; environmental factors; pasture management; forage conservation; silage; fertilization; breeding strategies; multi-species sward; climate adaptation; and hay. The focus was on studies published in the last decade, with a particular emphasis on those that assess both agronomic and breeding methods aimed at improving forage quality. The review synthesises the findings from the selected studies, comparing different methods for improving forage quality in permanent grasslands and their effects on ruminant productivity. By highlighting common trends and discrepancies across studies, this work aims to identify gaps in current research and offer recommendations for future studies.

3. Characteristics of Forage from Permanent Grasslands

The primary forage from grasslands is fresh pasture fodder, consumed directly by grazing animals during the growing season [20]. It is rich in protein, vitamins, and minerals, making it a vital nutrient source for ruminants. Pasture quality depends on its botanical composition—grasses, legumes, and forbs—as well as environmental factors like soil quality, water availability, and fertilization, which enhance growth and nutrition [21,22,23]. Early grazing stages yield higher protein and digestible fibre, optimizing nutrient utilization. Strategic grazing, including rotation length and sward height before and after grazing, further improves quality [24,25,26]. Spring swards are particularly nutritious, while reproductive-stage swards in summer have higher fibre and lower digestibility.

Hay, another essential feed, is produced by drying cut grasses and legumes to achieve over 85% dry matter, preventing fermentation and mould growth [27,28]. Early harvested hay contains more protein and less fibre, enhancing digestibility. Efficient drying processes preserve nutritional value, though rain can reduce quality and increase mould risks. High-quality hay is greenish, aromatic, and palatable, with storage methods and duration also impacting its nutritional value [29,30].

Silage is widely used in Europe due to its ability to preserve nutrients in moist forage under anaerobic conditions. Effective ensiling depends on factors like proper compaction, sealing, and optimal dry matter content. Bacterial inoculants are often used to enhance fermentation and minimize nutrient losses [31]. Wilted forage with 40–60% water content reduces losses compared to fresh plants [32]. Properly managed silage supports ruminant health and productivity by maintaining nutrient richness and improving fermentation efficiency. Grass silage or grass and legume silage well protected with foil is easier to store without the use of livestock buildings on the farm.

4. Forage Quality Evaluation

4.1. Chemical Composition of Forage

Forage quality refers to the ability of animals to efficiently consume forage and convert its nutrients into products such as milk or meat. It encompasses key attributes like nutritive value, palatability, and digestibility, essential for formulating balanced rations that meet livestock nutritional needs. Chemical analyses, supported by predictive systems such as NorFor (Nordic Feed Evaluation System), NRC (National Research Council), and INRA (French National Institute for Agriculture, Food, and Environment), are commonly used to evaluate forage quality [33,34,35]. These models assess parameters including dry matter (DM), crude protein (CP), acid detergent fibre (ADF), neutral detergent fibre (NDF), lignin (ADL), and ash.

CP measures all nitrogen-containing compounds in forage, including non-protein nitrogen (NPN) like nitrates and urea. It is a critical metric for evaluating forage quality, typically determined using the Kjeldahl method or combustion analysis. As plants mature, CP content decreases, reducing nutritional value. Digestible protein constitutes approximately 70–72% of total CP, with the remainder often rendered unavailable due to factors such as heat damage during fermentation.

The crude protein (CP) content, although commonly used to assess forage quality, does not fully reflect the true nutritional value of protein from a ruminant nutrition perspective. More accurate indicators include rumen degradable protein (RDP) and rumen undegradable protein (RUP), as defined by systems such as the Cornell Net Carbohydrate and Protein System (CNCPS) [36]. These protein fractions differ in their site of digestion and biological efficiency, thereby directly influencing microbial protein synthesis in the rumen and overall animal performance.

Moreover, the amino acid composition of forage—particularly the levels of essential amino acids such as methionine and lysine—is a critical determinant of protein quality [37]. While microbial protein serves as the primary amino acid source for ruminants, the amino acid profile of RUP (bypass protein) becomes increasingly important in high-producing animals, where microbial synthesis alone may not fulfil total amino acid requirements.

NDF, composed of cellulose, hemicellulose, and lignin, indicates potential forage intake. High NDF levels generally reduce intake, especially in high-producing animals. For example, in grasses, NDF values exceeding 600 g kg⁻¹ DM are often associated with reduced intake potential, while values below 500 g kg⁻¹ DM are considered more favourable. In legumes, due to their naturally lower fibre content, NDF levels below 450–500 g kg⁻¹ DM are typical and generally acceptable for maintaining high intake. ADF, consisting of cellulose and lignin, measures digestibility. Lower ADF levels are preferred as they indicate higher digestibility and energy availability. For instance, ADF values below 300 g kg⁻¹ DM are generally desirable for high-producing dairy cows, whereas values above 350 g kg⁻¹ DM may indicate more fibrous and less digestible forage.

Lignin, a component of fibre, reduces both digestibility and intake potential while providing no direct energy value. Its concentration is a key factor influencing forage utility.

Beyond its nutritional composition, forage fibre also plays a key physical role in maintaining rumen health. Physically effective NDF (peNDF) stimulates chewing activity and salivation, both of which are essential for buffering rumen pH [38,39]. This effect helps prevent subacute ruminal acidosis, particularly in high-concentrate diets. Only forage fibre can provide this structural function, emphasizing the importance of both quantity and physical form of fibre in ration design.

Recently, fibre digestibility has become an important parameter used to predict the energy concentration in forage and the efficiency of its utilization. Indicators such as neutral detergent fibre digestibility (NDFD) and total-tract NDF digestibility (TTNDFD) help reveal significant differences between forages that are not apparent when relying solely on NDF and ADF content. They show how effectively fibre contributes to animal performance. For example, the meta-analysis by [40] showed that each 1-percentage-point increase in in vitro NDF digestibility (NDFD) is associated, on average, with an increase of 0.17 kg in dry matter intake (DMI) and 0.25 kg of 4% fat-corrected milk per cow per day. In addition, in vitro dry matter digestibility (IVDDM) is increasingly used to evaluate the total digestible fraction of forage biomass. IVDDM accounts for both the composition of the cell wall and fermentation dynamics, allowing for a practical prediction of actual energy availability under rumen-like conditions [41].

Ash content represents the total mineral content of forage and provides insights into its macro- and micronutrient balance. Excessive ash may indicate soil contamination. Monitoring ash ensures nutritional standards are met without impurities.

Minerals are vital for livestock health and productivity. Macronutrients like calcium (Ca), phosphorus (P), potassium (K), and magnesium (Mg) support metabolic functions, while micronutrients such as cobalt (Co), copper (Cu), manganese (Mn), and selenium (Se) are critical for enzymatic processes [42]. Nitrogen (N), along with phosphorus and potassium, is especially important for assessing forage’s nutritive value [27].

4.2. Energy and Forage Value Calculations

Core forage analyses provide key metrics such as total digestible nutrients (TDN), net energy (NE), and relative feed value (RFV), offering a detailed evaluation of forage nutritional contributions [42]. Net energy (NE) measures the energy available to livestock for maintenance, growth, reproduction, or lactation, calculated by subtracting faecal, urinary, gaseous, and heat losses from the gross energy content. For hay, haylage, and grass silage, NE values can also be estimated using acid detergent fibre (ADF) content, making it highly useful for ration formulation [43].

Total digestible nutrients (TDN) represent the digestible portion of feed and serve as a key indicator of energy content. TDN values, derived from digestion trials or calculated using ADF levels, can sometimes overestimate actual energy availability, as they do not account for losses during ruminal fermentation. For this reason, NE is often considered a more accurate measure of usable energy [44].

Relative feed value (RFV) combines digestibility (ADF) and intake potential (NDF) into a single index, allowing comparison of forage quality within the same category. The use of RFV should be limited predictions only with cool-season species. While popular for ranking forages, RFV lacks the precision needed for detailed ration balancing [45]. To address these limitations, the Relative Forage Quality (RFQ) index has been developed [46,47]. Calculations of RFQ differs from RFV. While RFV is based on ADF and NDF, the RFQ includes additional parameters such as CP, fat, ash, and most importantly, the digestibility of NDF. By incorporating NDF digestibility, RFQ provides a more accurate estimate of the energy available from forage. Unlike RFV, RFQ accounts for both intake and digestible energy, which makes it more relevant for predicting animal performance. It is especially useful for evaluating forages from grasses and legumes with varying fibre digestibility. Still, both RFV and RFQ are best suited for classification and market comparison, rather than as standalone tools for precision nutrition.

4.3. Parameters for Silage Evaluation

Evaluating silage quality involves analysing key parameters reflecting fermentation efficiency and nutritional value [48]. Dry matter content significantly impacts fermentation dynamics and feed quality. Optimal DM levels (30–50%) ensure proper fermentation and minimise nutrient losses. Low DM (<30%) increases effluent losses and undesirable fermentations, while high DM (>50%) complicates compaction and raises spoilage risks. Regular DM assessment supports effective preservation and ration balancing.

Acidity (pH) is another critical parameter, indicating silage acidity. It depends on the plant’s buffering capacity and fermentation efficiency. High-quality silages exhibit low pH levels, driven by lactic acid production, which should account for 65–70% of total organic acids to minimise energy and DM losses.

Acetic acid is present in smaller amounts, but concentrations above 4–6% of DM may indicate prolonged fermentation or poor compaction. However, silages with Lactobacillus buchneri inoculants tolerate higher acetic acid levels, improving aerobic stability.

Butyric acid serves as a marker of clostridial fermentation and is undesirable. Levels >0.5% of DM suggest nutrient degradation and reduced palatability, potentially affecting livestock performance and increasing metabolic disorder risks like ketosis.

Ammonia (NH₃) levels indicate protein breakdown during fermentation. Excess ammonia (>12–15% of CP) is often linked to slow pH drops or clostridial activity, potentially disrupting rumen nitrogen balance and reducing productivity.

Ethanol levels reflect yeast activity. Low concentrations (typically <1–2% of DM) are considered normal, while higher levels (>3–4% of DM) indicate excessive fermentation, leading to DM losses and spoilage risk. Although most ethanol is metabolized in the rumen to acetic acid, high ethanol levels may negatively affect feed intake and alter milk flavour.

4.4. Microbiological Assessment of Forages

Microbiological analysis, including the detection of moulds and mycotoxins (e.g., aflatoxins and deoxynivalenol), is essential for assessing forage quality and safety, particularly its potential health effects on livestock. Fungal contamination poses risks to both animal and human health through the food chain.

Yeasts, such as Candida and Saccharomyces, and moulds are common forage contaminants. Yeasts, as facultative anaerobes, ferment sugars into ethanol and carbon dioxide in oxygen-deprived environments, reducing sugar availability and potentially altering milk taste. In the presence of oxygen, yeasts degrade lactic acid, raising silage pH and promoting mould growth. Poor storage, like oxygen infiltration, exacerbates yeast activity, while organic acids (e.g., formic, acetic acid) inhibit their growth [49].

Moulds thrive in oxygen-rich conditions, particularly in wet hay or improperly compacted silage. Common species include Aspergillus, Penicillium, Fusarium, and Mucor. Mould contamination not only reduces forage nutritional value but can cause respiratory diseases, allergies, and toxicosis in animals. Aspergillus fumigatus, associated with forage putrefaction, is a notable pathogen linked to mycotic haemorrhagic bowel syndrome (HBS) in immunosuppressed dairy cattle [50,51]. It produces gliotoxin, a mycotoxin that suppresses immunity, increasing its infectivity [52].

4.5. Methods for Forage Evaluation

Forage quality has traditionally been assessed using physical parameters such as colour, leaf content, maturity, odour, softness, purity, and palatability. While valuable, these criteria are subjective and difficult to standardise [38]. Modern evaluation methods combine chemical analyses with advanced techniques like near-infrared reflectance spectroscopy (NIRS) and increasingly incorporate microbiological parameters [53,54].

Traditional wet chemistry remains the most widely used method for forage evaluation. It relies on well-established chemical and biochemical principles to provide accurate and detailed results, though it requires significant time and resources to complete.

NIRS links chemical composition with energy changes in the near-infrared range (800–2500 nm) [55,56]. This rapid, non-destructive method requires minimal sample preparation and predicts multiple nutritional factors, making it cost-effective once calibrated for specific crops [57]. It offers advanced solutions in monitoring forage quality (such as moisture, DM contents, protein, fibre, lipids, and metabolizable energy contents) [58,59]. However, its accuracy may decrease with diverse forage types [42].

Studies on temperature and agro-climatic indicators indicate that cumulative temperature at cutting, alone or with agro-climatic and chemical criteria, effectively predicts forage feed value [60,61,62,63]. A positive correlation between plant maturity and cumulative temperature during the first growth cycle has been observed [61,64].

Animal-based methods for evaluating forage quality include in vivo digestibility studies, feed intake measurements, and assessments of forage effects on animal productivity. Digestibility is determined using total collection or marker methods, while voluntary intake is measured under ad libitum conditions. Milk yield and live weight gain serve as indicators of forage nutritional value, and rumen fermentation analysis along with nitrogen excretion studies help assess metabolic efficiency. Advanced techniques, such as rumen cannulation, allow direct examination of digestive processes and forage degradation [65].

5. Factors Affecting Forage Quality from Grasslands

5.1. Environmental Factors

Temperature and precipitation are critical factors influencing forage yield and quality, directly affecting plant growth, botanical composition, nutrient concentration, and digestibility. They also regulate forage characteristics indirectly by influencing nutrient cycling in the soil [66,67,68].

Recent climate changes, including rising temperatures and variable precipitation, have prompted research on their effects on forage production [69,70]. Studies on temperature effects yield mixed results: Nordheim-Viken et al. [71] found that higher temperatures (day/night: 25/20 °C and 30/25 °C) increased CP and decreased cell wall content, while others observed opposite trends [60] or no effect [72]. Similarly, digestibility outcomes vary, with some studies finding no impact on whole-plant digestibility [72] and others reporting a decrease in OMD (organic matter digestibility) across plant parts.

Precipitation variability also affects forage quality. Reduced precipitation can lower ADF and increase WSC (water soluble carbohydrates) without significantly altering nitrogen content [73]. Greater variability may decrease yield while improving crude protein and fibre levels, with shifts in functional group composition leading to less grass biomass and more forbs [74].

Climate change accelerates plant maturation, reducing forage nutritional value. Deroche et al. [75] observed a 6-day advancement in cutting dates over 32 years, alongside a 13% increase in cumulative temperatures. This led to a 22% reduction in crude protein, an 8% rise in crude fibre, a 3% decline in OMD, and a 9% increase in VDMI (voluntary dry matter intake). Adjusting cutting dates annually may be necessary to maintain both optimal forage maturity and nutritional quality.

Changes in abiotic factors (non-living elements of the environment, such as water, soil, chemistry, temperature, and humidity) and community composition also affect forage quality. Nutritive value depends more on functional group proportions than species diversity [76,77]. For example, legumes influence crude protein, while grasses affect fibre content.

5.2. Soil Fertility and Nutrient Availability

Soil fertility refers to the soil’s ability to provide essential nutrients for plant growth and development. Key factors include pH, organic matter, nutrient availability, texture, and microbial activity. Fertile soil contains balanced macronutrients (N, P, K, Ca, and Mg), micronutrients (Fe, Zn, and Cu), OM (organic matter), water, and active microbial communities. Nutrient deficiencies significantly impact forage quality [78].

Nitrogen is often the primary limiting nutrient in grasslands, reducing plant protein content when deficient [79]. But excess nitrogen in fertilization can lead to accelerated vegetative growth of plants. This growth results in higher levels of structural fibre (NDF and ADF), which are more difficult for ruminants to digest, thereby reducing the digestibility of the forage. Phosphorus and potassium shortages lower carbohydrate levels, leading to energy deficits in forage, while sulphur deficiencies reduce essential amino acids like methionine and cysteine, affecting animal growth and milk production. In some cases, nutrient deficiencies, particularly of phosphorus, potassium, or sulphur, can also induce earlier plant maturation and lignification, resulting in reduced digestibility despite acceptable dry matter yield. Deficiencies in Ca or Mg can lead to skeletal issues and conditions such as grass tetany in cattle. Micronutrient shortages, such as zinc, manganese, or copper, compromise animal growth, reproduction, and immunity.

A study in the Netherlands [80] showed that soil fertility significantly influences the content of S, P, K, Na, Mg, and Ca in grassland forage. Soil structure and pH also affect nutrient availability; for example, low pH reduces phosphorus accessibility, limiting plant growth. Regular soil analysis and targeted fertilization improve forage mineral composition, supporting animal health and productivity.

5.3. Botanical Composition and Species Richness

Management practices such as fertilization levels, optimization of mowing frequency or rotational grazing, and environmental factors such as topography, water availability, nutrient levels, and light conditions affect the botanical composition and species richness of permanent grasslands [61,62,81,82,83]. These factors significantly shape vegetation structure, productivity, and forage quality.

Grasslands are composed of a diverse mix of grasses, legumes, forbs, and shrubs. In European intensive grasslands, the primary functional groups include grasses, legumes, and forbs. Legumes are characterized by their high nutritional value, particularly due to their protein-rich composition and high digestibility. Grasses are valued for their availability and good nutritional content, especially in their early growth stages. Forbs and other plants enhance dietary variety, although their nutritional profiles can be highly variable [84,85].

Grasses from Pyrenean hay meadows exhibited the lowest values for digestible dry matter (DDM), relative feed value (RFV), feed unit for lactation (UFL), and protein digestible in the intestine (PDI). These grasses also showed imbalanced Ca:P ratios and high K:(Ca + Mg) ratios [86]. In contrast, legumes demonstrated the highest protein content and favourable nutrient balances. Trifolium pratense L. (red clover) and Trifolium repens L. (white clover) are particularly rich in protein and minerals such as calcium, though they contain relatively low levels of sugars and fibre [87].

Forbs demonstrated intermediate nutritional values, with some metrics comparable to legumes, although their protein levels were generally lower [86]. Certain forbs were found to have nitrogen compound levels comparable to or even exceeding those of Lolium perenne L. (perennial ryegrass) [88,89]. Despite significant variability between individual forb species [84,90], forbs tend to contain higher levels of minerals compared to grasses and some legumes. Misztal et al. [91] reported that the mineral content in hay from species-rich meadows depends on the proportion of non-leguminous forbs and often satisfies the mineral requirements of extensively reared livestock.

In contrast to beneficial non-leguminous forbs, undesirable weed species can significantly diminish the quality and productivity of permanent grasslands. Non-toxic yet nutritionally poor species, such as Rumex obtusifolius L. (broad-leaved dock), Rumex acetosa L. (common sorrel), Cirsium arvense (L.) Scop. (creeping thistle), Heracleum sphondylium L. (hogweed), Anthriscus sylvestris L. (cow parsley), and others, often proliferate in response to overgrazing, inappropriate mowing regimes, nutrient imbalances, or insufficient competition from desirable forage plants. These species tend to have low palatability, elevated fibre content, and limited nutritional value compared to high-yielding grasses and legumes. Some, like H. sphondylium L. and Taraxacum officinale F.H. Wiggers coll. (dandelion), exhibit low dry matter content [86], posing challenges during forage conservation, particularly in haymaking. Prickly species such as C. arvense (L.) Scop. may deter grazing in their vicinity, while others like Rumex species and Juncus species occupy valuable sward space, further reducing pasture productivity. Moreover, under lax grazing pressure, livestock often avoid unpalatable species, unintentionally promoting their spread [92]. Further weed control strategies are discussed in Section 6.2.5.

While grasslands are essential for livestock, certain toxic plants pose significant risks to animal health. Species such as Senecio jacobaea L. (common ragwort), Aconitum napellus L. (monkshood), Equisetum arvense L. (field horsetail), and Colchicum autumnale L. (autumn crocus) contain toxic alkaloids or other harmful compounds [93,94]. Although their bitterness or odour generally deters consumption, forage shortages may lead to accidental ingestion, potentially causing symptoms such as colic, neurological disorders, or even death. Effective monitoring and management practices, such as regular field inspections, timely removal of toxic plants, and rotational grazing, are crucial to minimizing these risks [95].

Natural grasslands are recognized as species-rich habitats with high ecological and agricultural value. Traditionally, these areas were managed extensively [5], which supported high species richness. However, due to agricultural intensification, the number of plant species associated with semi-natural grasslands has significantly declined [96]. Nitrogen supplementation, a cornerstone of grassland intensification in Europe, boosts biomass production but reduces plant diversity due to competitive exclusion [97,98]. Increased competition for light in dense, fertilized swards disadvantages smaller, less competitive species [99]. A meta-analysis by Francksen et al. [100] found that nitrogen application rates negatively correlate with species richness, estimating a loss of ~1.5 species m⁻² for every 100 kg N ha⁻¹ year⁻¹ applied. The impact was more pronounced in diverse grasslands and under low defoliation rates, although responses varied across grassland types.

As a result, in lowland regions of Europe, intensified grasslands have become dominant. These grasslands are managed intensively, with frequent and earlier cutting, and are dominated by a smaller number of species, including L. perenne, Dactylis glomerata L. (cocksfoot), and T. repens. While forage quality from these species-poor grasslands is relatively easy to manage due to their uniformity, species-rich grasslands present greater variability in forage quality, which depends on species composition and abundance [101]. According to French et al. [102], grasslands with greater species richness in lowland England were associated with higher DM content, sugar levels, P concentrations, and even medicinal properties. Proper management practices, such as optimizing cutting frequency, fertilization levels, and rotational grazing, can enhance both botanical diversity and forage quality, ensuring ecological and agricultural benefits (Figure 1).

5.4. Developmental Stage and Harvest Date

The maturity of plants at harvest, especially during the first cut, is crucial for forage nutritional value [103,104,105,106]. As plants mature, their chemical composition changes, with increasing crude fibre (CF) content [107] and declining CP levels, reducing OMD and voluntary DM intake [108,109]. These changes occur at different rates depending on plant species, with grasses accumulating biomass rapidly in spring and summer, often accompanied by a sharp decline in digestibility [110,111].

Some species, such as D. glomerata and T. pratense, require earlier harvesting to prevent reduced digestibility and nutritional value caused by rapid maturation and lignification. Late-maturing grass varieties, such as L. perenne and Phleum pratense L. (timothy grass), delay the onset of lignification, which helps preserve a favourable ratio of protein to fibre. This extends forage quality and allows greater flexibility in harvest schedules, accommodating weather conditions such as prolonged rainfall without a significant loss of nutritional quality. However, optimal harvest timing must also consider prevailing weather conditions, as they can significantly affect forage quality and dry matter losses, requiring flexible scheduling to balance plant maturity benefits with environmental constraints. Additionally, later maturity can increase DM yields, improving production efficiency.

In addition to plant maturity, seasonal variations also influence forage quality. The nutrient content determining nutritional value changes throughout the growing season [112,113]. For example, the sugar content in the spring regrowth (first cut) is the highest, decreases in the second cut, and in the third (autumn) cut, it reaches approximately 80% of the first cut’s value. These fluctuations result from variations in growing conditions and changes in plant metabolism at different stages of the growing season. Therefore, the first cut is best suited for silage production, the second for hay, and the third, depending on needs, for either ensiling or drying.

5.5. Conservation Method

5.5.1. Hay Production

Significant DM and nutrient losses occur during forage harvesting (e.g., cutting and tedding/raking/baling) and storage, with the extent of losses varying by forage type and processing conditions. For instance, in hay production, DM losses typically range from 15% to 18% under optimal drying conditions [114]. However, rain damage can increase these losses to as much as 30%, and extended periods of poor drying may even lead to total crop loss. Deroche et al. [115] demonstrated that the soluble carbohydrate content of hay is primarily determined by that in the corresponding fresh forage, with drying time between cutting and baling playing a secondary role. On average, haymaking results in DM losses of 24–28%, with the majority occurring during harvesting [116]. Mechanical damage during haymaking, particularly during tedding and baling, can lead to substantial nutrient losses, especially in legumes, which are more prone to leaf shattering than grasses. Properly dried hay (with a moisture content below 20%) incurs minimal storage losses (approximately 5%) when stored under appropriate indoor conditions. In contrast, storage outdoors or under suboptimal conditions, especially in high-precipitation areas, may lead to significantly greater losses. Higher moisture levels encourage microbial growth and aerobic deterioration, thereby reducing nutritional value and posing risks to animal health.

5.5.2. Silage Production

Properly made silage is a safe and nutritious feed, free from health risks for both humans and livestock [117]. Silage production involves substantial nutrient losses, categorized as field losses (due to plant and microbial respiration, rain damage, and mechanical damage) and storage losses, with approximately half occurring during storage [118]. Plant and microbial respiration deplete carbohydrates, increasing protein and fibre concentrations. Rain damage exacerbates these effects by dislodging leaves, leaching nutrients, and stimulating respiration. Mechanical damage (more critical in hay than in silage) disproportionately affects nutrient-rich leaves, reducing the leaf-to-stem ratio and lowering forage quality.

During storage, microbial respiration depletes digestible nutrients, particularly nonstructural carbohydrates, while protein losses remain minor but may alter protein solubility, affecting feed utilization [119]. Fermentation losses in the silo primarily result from CO₂ production, with DM losses varying based on microbial species and substrate composition [31].

A significant source of losses in silage is aerobic deterioration [31,120]. When silage is exposed to air upon opening the silo or after its removal, fermentation acids and other substrates are oxidized by aerobic bacteria, yeasts, and moulds. Silage deterioration upon air exposure is inevitable and typically leads to substantial losses of DM and essential nutritional components due to the oxidation of lactic acid and WSC. This process reduces preservation potential, degrades nutrients, and can result in the formation of indigestible Maillard products due to excessive heating. The accumulation of degradation products can lower palatability and contribute to feed refusals. Additionally, some aerobic microorganisms, such as moulds, Bacillus species, and Listeria monocytogenes, pose health risks to livestock, while further aerobic deterioration may lead to the formation of potentially harmful mycotoxins. Preventing aerobic deterioration during feedout is a critical objective in every silage management program.

In addition, the microbes in well-preserved silage may offer probiotic benefits to livestock. Poorly fermented silages, however, often contain elevated levels of butyric acid, amines, and ammonia (NH₃), which are produced by Clostridia bacteria. These compounds can reduce feed intake and overall utilization by livestock. The primary health risk to livestock is ketosis, which can result either directly from butyric acid or indirectly from decreased energy intake due to poor silage quality [121]. Biogenic amines with biological activity, such as histamine, tyramine, putrescine, and cadaverine, can negatively impact feed intake and animal health. These amines may accumulate in dairy products, such as cheese, and are associated with headaches, nausea, and hypertension in humans [122]. Poor silage-making practices, particularly when the pH is not sufficiently lowered or when oxygen is present, can encourage the growth of harmful microorganisms. Among the most dangerous are Clostridium, Bacilli, Paenibacilli, Listeria, and E. coli [123].

Clostridium species are obligate anaerobes that thrive at high pH (>4.5), high forage moisture (>70%), and water activity levels (0.952–0.971). Rapid acidification to pH 4 or below within three days effectively inhibits their growth [124]. Pathogenic species include C. perfringens, C. difficile, C. tetani, and C. botulinum, with the latter being most associated with silage. C. botulinum produces botulinum toxin, one of the most potent neurotoxins, causing botulism [125,126]. Botulinum toxins are one of the most lethal substances known. Botulinum toxins block nerve functions and can lead to respiratory and muscular paralysis.

Bacilli and Paenibacilli are aerobic or facultatively anaerobic spore-formers found in silage, including Bacillus licheniformis, B. pumilus, B. coagulans, B. sphaericus, B. cereus, and Paenibacillus polymyxa [127]. Of these, B. cereus is particularly concerning due to its role as a foodborne pathogen. Bacillus cereus is frequently associated with food-borne intoxications, and its emetic toxin cereulide causes emesis and nausea after consumption of contaminated foods. In severe cases, especially in vulnerable individuals, B. cereus may also lead to diarrheal syndromes or opportunistic infections, and its spores can survive pasteurization, posing a risk even in processed dairy products. The major source for contamination is found within contaminated raw materials containing the highly chemically resistant cereulide, independent of vegetative bacteria cells [128]. Swedish studies identified soil as the main source of B. cereus spore contamination in raw milk during grazing, with sawdust bedding as a major source indoors [129].

Listeriosis, caused by Listeria monocytogenes, is often linked to silage. In ruminants, it primarily causes encephalitis, uterine infections (resulting in late-term abortions), and eye infections (silage eye). L. monocytogenes is a facultative anaerobic gram-positive bacterium found in soil, water, vegetation, and animal faeces [117].

Shiga toxin-producing E. coli (STEC) is a major cause of foodborne illness, with symptoms ranging from mild discomfort to severe diseases like haemorrhagic colitis and haemolytic uremic syndrome [130]. While most E. coli strains are harmless, pathogenic strains such as O157:H7 and others (O26, O103, O111, O145) are significant contributors to human infections [131]. A large variety of STEC has been identified in ruminants, which represent their animal reservoir, but only O157 and a few other serogroups have been firmly associated with severe disease in humans. Over the years, the incidence of STEC infection has gradually increased and remains a significant problem in public health. STEC infection causes diarrhoea and bloody diarrhoea, and in severe cases patients develop haemolytic uremic syndrome (HUS) and central nervous system (CNS) impairment [132].

5.6. Negative Compounds

Anti-nutritional factors (ANFs) are naturally occurring compounds in forage plants that can negatively impact animal performance, compromise health, or even lead to mortality. These substances interfere with nutrient absorption, digestion, and metabolism. Common ANFs include tannins, nitrates, alkaloids, cyanogenic glycosides, estrogens, and mycotoxins. The presence and effects of these substances vary depending on plant species (including weeds), seasonal changes, environmental conditions, and animal sensitivity. While many forage plants provide essential nutrients, some contain compounds that can reduce feed efficiency, impair health, or become toxic at high concentrations. Ensuring high-quality forage requires minimizing harmful levels of these substances.

Tannins are found in legumes (e.g., Lotus species and Trifolium species) and can bind to proteins, reducing their digestibility and impair microbial activity in the rumen. However, at low levels, tannins can have beneficial effects by reducing protein degradation and methane emissions. Tannins are a key chemical defense that plants use against mammalian herbivores. To cope with tannins, many herbivores have evolved salivary tannin-binding proteins that precipitate tannins in forage items and thus minimize their deleterious effects. In the past, one specific type of salivary tannin-binding protein was identified (proline-rich proteins) and has been found in a range of mammalian species. However, there are other proteins in the saliva of mammalian herbivores that also have a high tannin-binding affinity, which may allow for tolerance of low-quality food resources. Notably, goats and sheep produce specific salivary proteins that effectively bind and neutralize many toxic plant compounds, including tannins, allowing these species to tolerate tannin-rich diets without adverse effects, a trait that is not observed in cattle, which are more susceptible to tannin toxicity due to the absence of such protective mechanisms. So, Capra hircus (domestic goats) are able to survive on low quality, tannin-rich food items [133]. Tannins are a group of polyphenolic compounds that are widely present in plant regions and possess various biological activities including antimicrobial, anti-parasitic, anti-viral, antioxidant, anti-inflammatory, and immunomodulation. Therefore, tannins are the major research subject in developing natural alternative to in-feed antibiotics. Incorporations of tannin-containing forage in ruminant diets to control pasture bloat, intestinal parasite, and pathogenic bacteria load is another important application of tannins in ruminant nutrition. Tannins have traditionally been regarded as an “anti-nutritional factor” for monogastric animals and poultry, but recent research have revealed some of them, when applied in appropriate manner, improved intestinal microbial ecosystem, enhanced gut health, and hence increased productive performance [134].

Alkaloids are found in Festuca arundinacea Schreb. (fescue grass) and Phalaris arundinacea L. (reed canarygrass) and can be toxic at high concentrations, causing neurological issues, vasoconstriction, and reproductive problems (e.g., “fescue toxicosis”).

Early spring crops often have elevated nitrate concentrations. This is mainly due to the plant’s uptake of fertilizer and soil nitrogen following mineralization, especially in low temperatures that slow protein synthesis [135]. While nitrate itself is not toxic to livestock, nitrite (NO₂⁻) poisoning can occur when forages high in NO₃⁻ are consumed. Normally, NO₃⁻ in the rumen is reduced to ammonia (NH₃) via NO₂⁻. However, excessive NO₃⁻ intake can cause NO₂⁻ to accumulate, reacting with haemoglobin to form methaemoglobin, which cannot carry oxygen. This condition, methemoglobinemia, varies in severity and may include reduced feed intake, abortion, respiratory distress, coma, or death [136].

Oxalates are present in Rumex species and can bind calcium and magnesium, causing hypocalcaemia (“big head disease”) in horses and kidney damage in ruminants.

Prussic acid, or hydrocyanic acid, is a toxic compound formed from the decomposition of cyanogenic glucosides in plants like sorghum (great millet) (Sorghum bicolor (L.) Moench) and sudangrass (Sorghum bicolor (L.) Moench nothosubsp. drummondii (Steud.) de Wet ex Davidse) [137]. Symptoms of prussic acid poisoning in ruminants include increased respiration, irregular pulse, staggering, frothing at the mouth, respiratory paralysis, or death. Ensiling has been shown to reduce prussic acid levels in various plant species. Phytoestrogens are plant compounds structurally and functionally similar to animal estrogens [138]. The main types include coumestans, lignans, and isoflavones [139]. Coumestans, such as coumestrol, are particularly abundant in alfalfa and T. pratense [140]. Among phytoestrogens, coumestans are the most potent [141]. In sheep, phytoestrogens can cause temporary or permanent infertility [142]. Similar effects are reported in cattle-fed diets containing alfalfa or T. pratense, with fertility problems observed in heifers consuming ensiled T. pratense high in estrogenic isoflavones [143]. Pyrrolizidine alkaloids (PAs) are heterocyclic compounds derived from necine base esters found in plants such as Heliotropium (Boraginaceae), Senecio (Compositae), and Crotalaria (Leguminosae) [144,145]. PAs cause liver cirrhosis in humans and liver and lung poisoning in livestock, with smaller herbivores (e.g., sheep, goats, and rabbits) showing greater resistance than larger species (e.g., cattle and horses) [144,146]. Seaman et al. [147] documented PA poisoning in cattle and horses consuming Senecio madagascariensis Poir. (Madagascar ragwort), Echium plantagineum L. (purple viper’s bugloss), and Heliotropium europaeum L. (common heliotrope), while [148] reported sheep mortalities from E. plantagineum and H. europaeum.

5.7. Fungal Contaminants in Forage

Mycotoxins, harmful secondary metabolites produced by fungi such as Aspergillus, Penicillium, and Fusarium, pose a significant threat to feed quality and animal health. Toxins like aflatoxins, ochratoxins, fumonisins, and deoxynivalenol (DON) can develop in improperly stored feed and persist in animal products such as milk, meat, and eggs, compromising their safety and quality. Chronic exposure to mycotoxins in livestock can lead to reduced productivity, fertility issues, and organ damage. Environmental factors such as high moisture, poor compaction, inadequate storage, and air infiltration increase the risk of fungal contamination. To mitigate these risks, regular microbiological monitoring, including mycotoxin testing, should be an integral part of forage quality control, particularly in temperate climates where conditions favour fungal growth [149].

Ergot alkaloids are a specific group of mycotoxins produced by grass-associated fungi, including Claviceps spp. and Neotyphodium spp., which infect grasses such as Festuca arundinacea and Lolium species [150]. Claviceps africana produces dihydroergosine in infected sorghum, while Neotyphodium spp. primarily produce ergovaline in tall fescue and ryegrass [151,152]. Tall fescue toxicosis has been linked to reduced weight gain in beef cattle [153]. In lactating dairy cows, consuming ryegrass silage with 1.78 mg kg⁻¹ of ergovaline resulted in reduced reproductive performance, increased mastitis incidence, and lower milk yield [154]. Symptoms of ergot alkaloid toxicity include feed refusal and severe declines in milk production [155]. Ensiling can reduce the toxicity of these compounds, with complete degradation of 2.63 mg kg⁻¹ of ergovaline after 140 days in tall fescue [156] and a nearly 50% reduction in dihydroergosine levels (from 0.85 to 0.46 mg kg⁻¹) in sorghum after 42 days [157].

5.8. Interactions Between Factors

The forage quality is influenced by many factors (Figure 2). An impact of environmental factors on the nutritional value of forages is multidimensional and complex. For example, the variable availability of water in the soil, dependent on rainfall and temperature, affects not only the development of the plant root system but also their chemical composition. When combined with intensive nitrogen fertilization, this leads to changes in the botanical composition of the sward, reducing the proportion of leguminous plants in favour of grasses. Such changes may improve digestibility in the early stages of growth but simultaneously lower the nutritional value as the plants mature.

6. Methods for Improving Forage Quality

6.1. Breeding Methods for Grasses and Legumes

The breeding of grasses and small-seeded legumes primarily relies on traditional methods such as selection, crossing, and mutagenesis [158]. Modern biotechnological techniques accelerate genetic gain in forage breeding [159]. Techniques like doubled haploids (DH), androgenesis, and protoplast fusion can shorten breeding cycles and improve selection efficiency, though their use in forage grasses remains limited. Molecular tools like marker-assisted selection (MAS) and genomic selection (GS), supported by AI, refine precision by early detection of superior genotypes early and analysing full genomes using AI-supported models [160]. Genome editing (e.g., CRISPR-Cas9), allows precise gene modification for stress tolerance and digestibility without introducing foreign DNA, easing regulatory acceptance [161,162]. Despite obstacles in grass transformation, transgenesis and RNA interference are still applied to enhance nutritional traits like reduced lignin and improved digestibility [163].

Genetic progress in forage crops is slow due to biological limitations and underinvestment. The estimated DM yield increase for L. perenne and T. repens is only 4–6% per decade, whereas in cereal crops, it reaches 10–15% [164,165]. Similarly, improvements in forage nutritional value, such as DMD, are progressing at a modest rate. In L. perenne, DMD has increased by only 5–10 g kg⁻¹ DM (0.5–1%) per decade [165]. To support the adoption of improved cultivar, economic indices such as the Pasture Profit Index (PPI) in Ireland and the Forage Value Index (FVI) in New Zealand and Australia have been developed. These tools assist in selecting forage varieties based on their economic value and adaptation to their environment [166,167].

An example of successful forage crop breeding is Festulolium (Festulolium Asch. & Graebn.), an intergeneric hybrid between species of the Festuca and Lolium genera [168], which combines the high nutritional value and productivity of ryegrass with the stress tolerance of fescue. It offers improved persistence, disease resistance, and higher nutritional value making it valuable in intensive systems [169]. Other species, such as Lolium multiflorum Lam. (Italian ryegrass) and L. perenne have been improved for better digestibility and stress resilience [170]. Selection for high WSC content has enhanced ruminant digestion efficiency and reduced methane emissions, while tetraploid Lolium varieties, show lower fibre content and higher digestibility due to anatomical differences [171].

In the Festuca genus, breeding efforts have focused on increasing the leaf-to-stem ratio [172]. Meanwhile, legume breeding has emphasized the improvement of T. pratense and T. repens. T. pratense breeding has seen some focus on improving feed value and reducing phytoestrogen level [173,174], whereas T. repens breeding has aimed at improving DM yield, persistence, and nutritive value [21].

A complementary breeding objective in forage legumes is the reduction of antinutritional factors. For example, cultivars of T. pratense such as ‘Grasslands G27’ have been developed with lower formononetin levels, improving reproductive performance in ewes and enhancing palatability, although potentially at the cost of reduced disease resistance. To maintain sward persistence, traits such as increased tiller density were also selected [175]. In Lotus corniculatus L. (bird’s-foot trefoil) breeding targets focus on selecting genotypes with moderate tannin levels (2–4% of DM), which help prevent bloat and improve protein utilization without impairing digestibility [176].

Forage breeders must balance the need for higher productivity with increasing expectations for sustainability and climate resilience. Breeding aim to develop varieties adapted to temperature fluctuations, changing precipitation, and longer growing seasons [177]. As genetic diversity in dominant forage species is limited, alternative species such as L. corniculatus, Lotus pedunculatus Schkuhr. (greater bird’s-foot trefoil), Onobrychis viciifolia Scop. (sainfoin), Cichorium intybus L. (chicory), and Plantago lanceolata L. (english plantain) are being considered for their functional traits. While expanding species range enhances genetic potential, it also stretches breeding resources.

European-derived F. arundinacea cultivars are widely used in pasture-based systems, where endophytes contribute to host plant fitness but may negatively affect livestock via ergot alkaloids, leading to fescue toxicosis [178,179]. Removing endophytes improves animal performance [180], but such cultivars show poor persistence under stress [181]. Thus, tall fescue infected with selected endophytes has been introduced, showing better production and survival under variable conditions [182,183]. Strains AR542 and AR584 of Neotyphodium coenophialum, used in the U.S., New Zealand, and Australia, enhance stress tolerance and reduce insect pressure without producing toxic alkaloids [184,185]. Thus, most programs still focus on three primary species: diploid and tetraploid L. perenne, T. repens, and T. pratense. Future breeding priorities include enhancing protein and mineral content, improving fatty acid profiles, increasing anthelmintic and bloat-safe properties, optimizing nitrogen fixation rates, modifying root architecture, improving nitrogen and phosphorus use efficiency, reducing methane emissions, and improving compatibility in multi-species swards [186].

6.2. Renovation Methods

Over the last 50 years approximately 60% of the world’s grasslands have experienced varying degrees of degradation [187]. Grassland renovation involves techniques designed to enhance productivity, biodiversity, and forage quality [188]. In Europe, a variety of grassland restoration methods have been implemented, with overseeding and reseeding being the most commonly used approaches. The choice of an appropriate restoration method depends on local conditions, including soil type and the extent of sward degradation. In certain grasslands, particularly those in areas prone to flooding or erosion, low productivity is often caused by nutrient deficiencies. In such cases, rational fertilization practices play a crucial role in restoring soil fertility and supporting the sustainable use of grasslands.

6.2.1. Overseeding

Direct overseeding enriches the species composition of permanent grasslands by introducing desirable grass or legume seeds into existing swards without significantly disturbing the soil structure [189]. This cost-effective and minimally invasive method is particularly suitable for improving the density and composition of slightly degraded but still productive grasslands.

For direct overseeding, commonly used machinery includes Vredo (Vredo Dodewaard BV, Dodewaard, The Netherlands), Köckerling Herbamat (Landmaschinenfabrik Köckerling GmbH & Co. KG, Verl, Germany), and Moore seeders (Moore Unidrill Manufacturing Ltd., Bourne, UK), which employ narrow slit-sowing technology (Figure 3). These tools introduce seeds into the soil through various mechanisms, such as disc, drill, or knife systems, in combination with proper sward preparation and post-seeding management. The Vredo seeder utilizes two discs arranged in a V-shape, creating narrow cuts in the grassland turf for precise seed placement [190]. Similarly, the Moore overseeding aggregate uses cutting discs combined with a seed-sowing system, cast iron packing wheels, and rubber support wheels. This design ensures that seeds are placed into slits approximately 4 cm deep, which are first made by cutting discs and then widened by a special wedge located next to the packing wheel. Seeds are delivered through pipes positioned just behind the wedge, and the slits are closed by the cast iron packing wheels [191].

To enhance overseeding success, selective herbicides are often applied to control undesirable weeds, especially those harmful to animals or highly competitive with valuable grass species. Chemical weed control is typically performed in spring or autumn, prior to reseeding or renovation efforts. For effective application, the sward should be mown or grazed beforehand, with a regrowth period of 3–4 weeks to ensure optimal herbicide uptake. Despite its benefits, herbicide use is often underestimated by farmers due to concerns about residue accumulation in pasture swards and potential risks to animal health [192].

6.2.2. Reseeding

Reseeding is a more intensive process that involves ploughing and reseeding the entire field. This method is particularly effective for restoring unproductive grasslands with poor species composition, severe weed infestations, or advanced soil degradation. Reseeding allows for the introduction of high-yield, nutrient-rich forage species, significantly enhancing herbage quality and productivity. However, it also comes with notable drawbacks, including high labour and energy requirements, temporary unavailability of the grassland for grazing or harvesting, and increased greenhouse gas emissions resulting from the mineralization of soil organic matter during cultivation [193].

A common challenge associated with reseeding is the rapid emergence of weeds from the soil seed bank, which necessitates additional weed control measures. For heavily weed-infested grasslands (with over 60% weed cover), applying total herbicides containing glyphosate prior to full tillage is an effective strategy to eliminate undesirable weeds along with the old sward. McQueen et al. [194] show persistent negative effects on nematode diversity across all four years. In addition, compositional shifts and changes in nematode-specific functional indices indicated less healthy soils in herbicide-treated plots. No recovery of nematode communities in glyphosate-treated plots was observed after four years, demonstrating the longevity of effects. This study reports negative off-target effects of glyphosate herbicide restoration projects on belowground diversity and the need to consider these factors in evaluating the long-term success of herbicide-based grassland restoration.

The most common reseeding method involves full tillage of the soil, followed by the sowing of a legume–grass seed mixture. To ensure optimal seed-to-soil contact, rolling with a meadow roller immediately after sowing is recommended. Once the new sward reaches a height of 10 cm, conservation mowing is advised, cutting the sward to a height of 6 cm to encourage healthy growth and establish a dense, productive sward [195].

6.2.3. Simplified Tillage Methods

To mitigate some of the challenges associated with conventional reseeding, simplified tillage methods have been introduced. These techniques minimize soil disturbance by restricting interventions to the upper soil layer (up to 5 cm depth) using tools such as disk harrows, band sowing equipment, or direct seeding techniques. Compared to ploughing and full tillage, simplified tillage is more environmentally sustainable, as it reduces soil erosion and lowers greenhouse gas emissions [196].

6.2.4. Species for Grassland Renovation

Species used in grassland renovation are selected based on site-specific conditions and the intended land use (Figure 4). Examples of high-quality grasses include L. perenne, Festuca pratensis Huds. (meadow fescue), D. glomerata, and P. pratense (which are highly valued for their digestibility and strong regrowth potential. Legumes, such as T. repens, T. pratense, and L. corniculatus, play a vital role in enhancing the CP content of forage. A recent trend in grassland renovation involves the use of multi-species swards, combining three groups: grasses, legumes, and forage forbs [197,198,199]. Forbs like P. lanceolata, C. intybus, and Achillea millefolium L. (yarrow) not only improve forage palatability but also provide bioactive compounds that support animal health and overall productivity. Certain species offer additional benefits. For example, C. intybus (chicory) and P. lanceolata contain high concentrations of magnesium and calcium, which may reduce the risk of grass tetany on mixed-species pastures [200]. Additionally, L. corniculatus produces condensed tannins, which protect proteins from rumen degradation and enhance intestinal absorption, resulting in higher nutritive value, increased CP content, and improved livestock productivity [201]. Diverse plant mixtures not only enhance forage quality but also support ecosystem resilience by fostering biodiversity, improving soil health, and providing habitats for pollinators. However, the limited persistence of legumes and forbs in reseeded swards remains a challenge, often necessitating reseeding every three to four years to maintain productivity and control invasive weeds. Strategies such as tailored fertilisation, optimised grazing, and rotational practices can extend the longevity of these valuable plant species [202].

6.2.5. Weed Control

A major challenge in forage-based livestock systems is effective weed management. Control strategies should aim not only at suppressing current infestations but also at creating unfavourable conditions for future weed establishment. Approaches include preventive management, chemical and mechanical intervention, and biological control, ideally within an integrated weed management framework:

Preventive management through rational utilization: One of the most efficient ways to suppress weed development is through rational grassland use. Maintaining a dense, competitive sward by optimizing grazing pressure, timely mowing, balanced fertilization, and soil pH regulation creates a hostile environment for weed invasion [203]. Overseeding with fast-growing or persistent forage species can fill canopy gaps and reduce available light and space for undesirable plants. For example, incorporating forage forbs such as C. intybus or P. lanceolata into grass–legume mixtures has been shown to reduce weed infestations on sheep and beef farms [204].

Chemical control of weeds in grasslands: The selective use of herbicides is aimed at eliminating or significantly reducing the excessive proportion of undesirable weeds, especially those that can be dangerous to animals and those that are highly competitive with valuable grasses. Chemical control in grasslands can be applied in two periods: early spring and autumn. Herbicides should be applied to meadow sward no higher than 20 cm. After herbicide application, the sward is suitable for mowing or grazing after a period of 14–21 days, depending on the active substance used. Over the past five years, the range of selective and highly effective herbicides that can be used with this method has been reduced by up to 80%. Several active substances are currently available to farmers depending on recommendations and permissions in different countries: fluroxypyr, triclopyr, clopyralid, florasulam, MCPA, and 2,4D [205].

Mechanical control: Mechanical methods involve the physical removal of weeds using machinery or hand tools, without chemical inputs. They are particularly effective against annual and biennial species. However, many perennials, such as C. arvense L. Scop. or Rumex obtusifolius, can regenerate from roots or crowns and thus require repeated interventions. Mechanical control is especially relevant in organic farming systems, protected areas, or low-input pastures. Its efficacy increases when combined with overseeding and well-managed grazing regimes. According to research conducted in Ireland, the most effective method of controlling C. arvense was grassland reseeding, ploughing followed by sowing a grass–clover mixture [206]. This approach led to the near-complete elimination of Cirsium within one year. The authors noted that no other method, including fallowing or the use of herbicides, proved as effective in the long term.

Biological control: Though less widespread, biological control methods are gaining recognition. These include bioherbicides (microorganisms or their metabolites that suppress weed growth), as well as insect herbivores targeting specific species [207]. For instance, Gastrophysa viridula larvae feed exclusively on R. obtusifolius [208], while the beetle Chrysolina hyperici has been successfully introduced in New Zealand to manage Hypericum perforatum L. (St John’s wort) populations [209]. Selective grazing is another biologically informed strategy; when properly timed, sheep or goats can help reduce populations of broadleaf weeds such as Rumex species or Cirsium species. The classification of such practices may vary depending on context, but their effectiveness in certain systems is well documented.

6.3. Fertilisation Strategies

Optimizing fertilization and soil amendment strategies is essential for correcting nutrient deficiencies, enhancing plant growth, and improving forage quality. Regular soil and forage testing help identify deficiencies and ensure targeted supplementation, maximizing both biomass production and livestock performance. Effective grassland fertilization enhances not only yield but also the nutritional composition and palatability of forage.

6.3.1. Soil pH Optimisation

The first step in soil management is optimizing soil pH to improve nutrient availability. The content of aluminium, which is toxic to plants, increases in acidic soils and disturbs the growth of plants’ roots [210]. Calcium modifies soil pH but also reduces the toxic effects of aluminium in the soil [211]. Lime application raises soil pH, increasing the bioavailability of phosphorus and potassium [212]. This is particularly beneficial for legumes [213] and enhances forage nutritional quality [214,215]. Lime rates should be tailored to soil type and climate. High-magnesium lime also enriches the soil with magnesium, reducing the risk of hypomagnesemia in livestock [216].

6.3.2. Macronutrients

The key macronutrients applied on grasslands include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulphur (S) [217].

Nitrogen enhances amino acid synthesis and CP content in grasses, promoting leaf growth. However, excessive N application can reduce WSC levels, disrupting the energy-to-protein balance and potentially impairing livestock performance. While N has little effect on digestibility, it can enhance fibre digestion in nitrogen-deficient forages. However, high N levels may lead to nitrate accumulation, posing a toxicity risk to livestock [135]. In addition, surplus nitrogen often increases the proportion of non-protein nitrogen (NPN) in forage, which is less efficiently utilized by ruminants and contributes to elevated nitrogen excretion. From an environmental perspective, excessive N fertilization is associated with nitrate leaching and greenhouse gas emissions. In legumes, nitrogen application is generally economically unjustified, as it suppresses biological nitrogen fixation and may reduce nodulation efficiency, ultimately compromising sustainability.

Phosphorus is crucial for energy transfer in plants, promoting the synthesis of sugars and starches that contribute to energy-dense forage. It indirectly improves forage quality by increasing the proportion of legumes in mixed swards, though it does not directly affect intake or digestibility. Phosphorus deficiencies in livestock can manifest as reduced feed intake, bone-chewing, and rickets [218].

Potassium supports Ca and Mg uptake, balancing forage mineral composition and contributing to livestock health. While low soil K rarely affects animal performance, excess K can interfere with Ca and Mg absorption, increasing the risk of grass tetany, a metabolic disorder most prevalent in spring pastures [219].

In addition to these macronutrients, Ca plays a critical role in the structural development of plant cell walls, improving fibre digestibility and mineral availability. Adequate calcium levels in forage are essential for livestock bone health, milk production, and muscle function. Furthermore, calcium fertilization promotes legume growth [186], enhancing overall forage quality due to their naturally high CP and Ca content.

Similarly, Mg is vital for chlorophyll synthesis and directly influences photosynthesis and plant growth. Magnesium fertilization increases forage Mg content, mitigating the risk of metabolic disorders such as grass tetany in livestock [220]. Adequate Mg levels also enhance forage palatability and improve nutrient absorption in grazing animals.

Sulphur is a key component of amino acids, including methionine and cysteine, which are essential for protein synthesis. Sulphur fertilization enhances CP content and digestibility, particularly in sulphur-deficient soils. Additionally, S improves N utilization efficiency, ensuring a better protein-to-energy balance in forage, which supports optimal livestock performance. According to Ryant et al. [221], S fertilization increased sulphur levels in forage, with the highest concentration (0.27%) observed in the gypsum-treated variant. Additionally, elemental S application significantly increased nitrogenous compounds and net energy lactation values.

Depending on land use, soil type, and the botanical composition of the sward, especially the proportion of legumes, the recommended annual rates of macronutrients in temperate European climate are generally as follows: nitrogen (N)—60–160 kg ha⁻¹, phosphorus (P₂O₅)—30–60 kg ha⁻¹, potassium (K₂O)—60–120 kg ha⁻¹, and sulphur (S)—20–40 kg ha⁻¹.

For nitrogen, application rates must comply with legal regulations that vary across EU countries. Final nutrient doses should be based on soil test results, expected biomass yields, and the nutritional content of the forage. Nitrogen, potassium, and sulphur should be applied in split doses: the first in early spring and the rest after each cut.

Phosphorus, calcium, and magnesium fertilizers can be applied in a single dose, either in spring or autumn, depending on soil properties and weather conditions. In some cases, such as peat soils in high-rainfall areas, it is advisable to split the annual phosphorus dose into smaller applications to reduce the risk of phosphorus runoff into surface waters. The methods and timing of fertiliser application and incorporation into the soil are also important; these aspects are discussed in Section 6.3.5.

6.3.3. Micronutrients

Micronutrients (trace minerals) are critical for maintaining forage nutritional quality and supporting livestock health. Deficiencies in boron (B), molybdenum (Mo), copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe) can impair plant development and reduce forage nutrient density [222]. Selenium uptake and accumulation in plants is important to human and animal health as plants are the main dietary source of this vital micronutrient. Whereas selenium deficiency is a widespread problem, Se toxicity is a localised but serious issue in certain areas of the world. The uptake and bioavailability of selenium in plants are determined by the concentration and selenium speciation in soil and water and controlled by physico-chemical conditions [223]. Radujković et al. [224] found that soil micronutrients, particularly Zn and Fe, were significant predictors of biomass production. Together with soil physicochemical properties and the C:N ratio, they explained 32% of unique variation in biomass, compared to 24% explained by climate and nitrogen deposition. While herbage micronutrient concentrations often reflect soil micronutrient levels, this is not always the case [225]. Soil acidity is a key factor affecting micronutrient availability in forage plants. Supplementing soils with chelated micronutrient fertilizers or applying foliar sprays can effectively correct deficiencies, particularly in regions with naturally low micronutrient availability.

6.3.4. Beneficial Elements

On grasslands, beneficial elements such as silicon (Si), titanium (Ti), and iodine (I) are sometimes applied, even though plants do not exhibit clear deficiency symptoms for these elements [226]. When applied in small doses, these elements enhance plant growth and development, improve forage yields, and participate in specific biochemical processes that mitigate biotic and abiotic stresses such as drought, high temperatures, and salinity. Additionally, they stimulate nutrient uptake [227]. Borawska-Jarmułowicz et al. [228] highlighted the positive effects of Si fertilization, including increased CP content and reduced CF, NDF, and ADF levels in plants. Similarly, foliar Ti application was found to lower CF content while increasing concentrations of CP, monosaccharides, Ca, and Mg, thereby improving ionic ratios [229].

6.3.5. Organic Fertilisers

Organic fertilizers play a crucial role in maintaining soil fertility, enhancing soil quality, enhancing forage nutritional value, and reducing dependency on mineral fertilizers [230]. Grasslands can be fertilized using various organic materials, including slurry (a liquid–solid mixture), semi-solid manure (separated feces), and farmyard manure (feces mixed with straw) [231,232]. These fertilisers not only provide the plants with the basic macronutrients, but are also a source of all micronutrients [233].

Manure application generally increases DM yield, although its impact on forage quality varies. For instance, according to [217] neither the application rate nor timing of manure application had an impact on forage nutritive value. Simić et al. [234] found no significant effect on digestibility, whereas [232] observed an increase in CP content. Szewczyk et al. [235] demonstrated that grasslands fertilized with farmyard manure and complementary mineral fertilizers produced 55–60% more protein compared to unfertilized swards. On Nardus stricta grasslands, manure application significantly improved forage quality. Vîntu et al. [236] reported that applying 30 Mg ha⁻¹ of manure every two years increased CP content by approximately 32% (from 80.8 to 106.6 g kg⁻¹ DM) and P content by around 57% (from 1.4 to 2.2 g kg⁻¹ DM). At the same time, CF content decreased by roughly 22% (from 282.4 to 219.5 g kg⁻¹ DM), thereby significantly improving digestibility.

Cattle slurry is particularly effective at increasing CP concentrations, as demonstrated by [232], who reported values of 142.9 g kg⁻¹ DM in fertilized swards compared to 126.4 g kg⁻¹ DM in unfertilized ones. Duffková et al. [237] also noted slight increases in N, P, and K in Arrhenatherion grasslands, although Ca concentrations decreased.

Digestate, another organic fertilizer, is a promising substitute for mineral fertilizers [238]. Although its efficiency is slightly lower than cattle slurry due to reduced application rates, co-digestion of cattle slurry with manure, silage, and hay does not diminish its fertilizer value.

Organic fertilizers influence the botanical composition of grasslands [239]. Farmyard manure encourages the growth of diverse plant species, including protein-rich legumes like clovers (T. pratense and T. repens), which enhance forage quality [240]. Vîntu et al. [236] reported that applying 20–50 Mg ha⁻¹ of manure reduced the proportion of Nardus stricta L. (matgrass) from 73% to 3–12%, while increasing Festuca rubra L. (red fescue) and legumes (L. corniculatus, Trifolium species). However, fertilizer application rates must be managed carefully. Kacorzyk et al. [241] observed that sheep manure application at nitrogen rates below 69 kg N ha⁻¹ increased the proportion of legumes, whereas higher rates (69–103 kg ha⁻¹ N) favoured grasses at the expense of legumes. Similarly, Štýbnarová et al. [232] reported that cattle slurry promoted grass dominance in extensive grassland systems, but combining cow manure with dung-water under medium utilization regimes encouraged legume growth and improved forage protein content. Several techniques are available for organic fertilizer application that have different emission losses of nutrients, especially nitrogen [242]. Typical techniques are broadcast applications on the soil surface, such as splash plate or band spreading techniques, low trajectory slurry applications, such as trailing shoe or shallow injection methods [243,244], and narrow band applications.Huijsmans et al. [245] found that NH₃ losses during slurry application were reduced by up to 74% using shallow injection compared to broadcast application. A common approach to controlling NH₃ volatilisation from manure is to incorporate it into the soil using tillage or injection equipment, which typically reduces NH₃ losses by 50 to >90% compared to application on the soil surface [246]. Groot et al. [247] confirmed that shallow injection was always the most efficient application method in terms of nitrogen losses. Overall, NH₃ volatilization of total nitrogen varied from 27% to 98% with broad band application, 1% to 25% with shallow injection, and 8% to 50% with narrow band application. Consequently, new application techniques are required to reduce NH₃ emissions to the atmosphere. These techniques are based on lowering the pH of the liquid organic fertiliser [248] or on reducing the contact area of the applied organic fertiliser with the atmosphere. In addition, it should be considered that the regular use of sulfuric acid for acidifying liquid organic fertilizers leads to excess sulphur in the soil, and, as a result, leaching of sulphate into the groundwater might become a concern [249]. Applying organic fertilizers with injection techniques is oftentimes combined with the use of a nitrification inhibitor (NI) in order to reduce emission of the greenhouse gas N₂O, as well as nitrate leaching [250]. High-emission techniques such as broad band application are prohibited in Germany and the Netherlands, and therefore the use of low-emission techniques is mandatory [251].

The timing of fertilisation is a very important factor to avoid nutrient losses escaping and leaching from organic fertilisers. Mineral fertilisers are usually applied at the beginning of the growing season in spring and manure only after the first swath of the sward [252]. Compared to spring fertilisation at the beginning of the growing season, autumn fertilisation results in higher losses through nitrogen volatilisation, leaching and denitrification due to more frequent rainfall, and lower N uptake by plants. Based on a study in a European climate by [253], N losses after organic fertiliser application are up to 43% in September and up to 53% in October. According to a study by [254], in order to avoid nutrient losses, organic fertiliser amounts should be divided into smaller amounts (under subsequent sward regrowth), resulting in less nutrient leaching and lower N₂O emissions. Results from a number of scientific studies confirm that CH₄ emissions from manure applications typically occur within the first few days after injection; however, annual CH₄ fluxes vary among soils, with some acting as net CH₄ sinks or sources depending on landscape attributes, drainage, and weather conditions [255,256].

6.3.6. Plant-Growth-Promoting Bacteria

The emerging trend in forage production, including grasslands, involves the use of plant-growth-promoting bacteria (PGPB). These microorganisms enhance plant growth through various mechanisms, such as symbiotic and associative N-fixation, nutrient solubilization and mineralization, phytohormone synthesis, production of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, synthesis of volatile organic compounds, and induction of osmolyte accumulation, among others [257,258,259]. According to [260], inoculation of L. perenne and T. pratense with Herbaspirillum sp. AP21, combined with 50% of the required nitrogen application rate, resulted in increased shoot dry weight, CP content, and shoot N levels while reducing NDF concentration. PGPB inoculation also altered the rhizosphere bacterial community structure, which was associated with improved forage growth and quality. These findings suggest that PGPB inoculation has significant potential to enhance the growth of ryegrass-red clover systems while reducing nitrogen fertilization requirements.

6.4. Mowing Intensity

The quality of forage from mown grasslands depends on several key factors, including the timing of mowing, frequency of use, cutting height, and sward maintenance practices. Proper management of these elements primarily influences the botanical composition of the sward, which in turn affects the nutritional value and digestibility of the forage.

For grasslands, the timing of the first cut (cutting date) is particularly important, as it should be based on the flowering stage of the dominant grasses. Therefore, meadows should be mown during the heading stage of the dominant grass species, which increases CP content, reduces CF levels, and improves digestibility. In contrast, delayed mowing leads to increased lignin content, which lowers the nutritional value of the forage [107,261].

Another crucial factor is the intensity of use, meaning the number of cuts during the growing season. According to [262], increasing cutting frequency significantly enhances forage quality, including CP and mineral content, digestibility, and rumen degradability. Extensive utilization, on the other hand, increases CF content, while reducing energy value and OMD. Research suggests that moderate (three cuts per year) and intensive utilization (four cuts per year), combined with nitrogen fertilization, represent optimal management practices for improving forage quality [263].

While more frequent and earlier mowing is generally associated with improved forage quality, particularly higher digestibility, crude protein content, and lower fibre fractions, it also presents agronomic trade-offs. Repeated early cuts can reduce carbohydrate reserves in plant root systems, weaken regrowth capacity, and shorten the lifespan of desirable forage species. Over time, this may lead to thinning of the sward, increased susceptibility to weed invasion, and loss of botanical balance. Thus, optimizing mowing intensity involves balancing the goal of high forage quality with long-term stand persistence and productivity.

6.5. Grazing Management Strategies

Among the management-based methods for improving forage quality in permanent grasslands, grazing systems play a key role, directly influencing nutrient composition, regrowth, and plant structure. Effective grazing management is essential for sustainable pasture use, optimizing both forage quantity and quality for livestock. It involves regulating stocking rates, selecting appropriate grazing methods, and controlling defoliation intensity (the removal of plant material by livestock) [264]. Grazing frequency, intensity, and duration significantly impact plant regrowth, pasture productivity, and nutrient retention.

A grazing method determines how livestock are managed across the landscape to optimize forage availability and ecosystem sustainability. In grassland ecosystems, the restoration of natural grazing systems is widely used as a restoration tool and has led to an increase in desirable and naturally valuable plant species [265]. Many studies demonstrate the benefits of site-adapted low-intensity livestock grazing [266,267]. At appropriate levels, grazing by goats and cattle can control woody species without damaging target species in temperate and Mediterranean grasslands [268]. In productive subtropical grasslands, periodic deferral of grazing can help mitigate the effects of overgrazing in ecosystems where grazing at lower stocking rates is beneficial [269]. Grazing animals can disperse seeds and promote grassland regeneration [270]. Pastures require a certain level of grazing to persist as potential habitats for certain grassland species of conservation concern [271]. However, within these habitats individual livestock can pose direct and indirect threats to such species. Accordingly, areas within pastures where grazing is detrimental may cover only a few square meters, while grazing the remaining habitat area may be desirable from a conservation point of view.

In many permanent grasslands, particularly those that are steep, remote, or difficult to access, undergrazing has become a growing problem. Limited accessibility makes it labour-intensive to install physical fences and manage livestock, leading to insufficient grazing and the spread of undesirable woody species, such as green alder in alpine regions. In such areas, virtual fencing can offer a practical and cost-effective alternative to physical fencing, helping to maintain appropriate grazing pressure and limit shrub encroachment.

Virtual fencing (VF) is an emerging technology that creates virtual boundaries for livestock. Collars equipped with positioning systems, such as GPS, emit acoustic warning signals if an animal approaches the virtual fence and an electric impulse if it continues to move forward, deterring it from crossing the virtual fence. Compared to physical fences, virtual fences, combined with positioning systems, enable precise tracking of individual animals and fencing out small areas within pastures at high spatio-temporal resolutions and low cost. VF has the potential to enhance agri-environment schemes aimed at conserving biodiversity [272].

The two primary grazing systems are continuous and rotational grazing. Continuous grazing is a traditional approach in which livestock have unrestricted access to pasture throughout the season. Grazing systems have a great potential to promote welfare, but domestic animals face risks, including lack of or poor access to food, shade and water, grazing in uneven or rocky areas, exposure to extreme climatic conditions, predation, and parasitism [273,274]. The two primary grazing systems are continuous and rotational grazing. Continuous grazing is a traditional approach in which livestock have unrestricted access to pasture throughout the season. While it is easy to implement, it often reduces pasture productivity and quality as plants lack sufficient recovery time. In contrast, rotational grazing is a more strategic system that divides pastures into paddocks, which are grazed sequentially [275]. This method increases stocking density, improves forage utilization, and enhances biomass production [276,277]. Rotational grazing allows farmers to extend the grazing season, regulate grazing intensity, provide optimal rest periods for plant recovery, renew carbohydrate reserves, and improve both pasture persistence and yield. Scientific research indicates that rotational grazing can boost forage productivity by 30–50% compared to continuous systems. Additionally, forage grown under rotational grazing contains higher CP levels (16–22%) and improved digestibility, both of which are essential for livestock health and performance [201]. For example, Daniel et al. [278] found that horses grazing on rotationally managed pastures consumed forage with significantly higher levels of digestible energy (DE), WSC, and sugars, leading to better weight gain and metabolic efficiency. However, while rotational grazing offers substantial benefits, it requires greater management and longer rest periods than continuous grazing. To maintain forage quality, it is crucial to keep residual grass height at 7–10 cm, ensuring continuous regrowth and preventing protein losses of 10–20%. By carefully balancing grazing intensity with plant recovery, rotational grazing enhances both pasture sustainability and livestock productivity. Similar to rotational grazing is guarded grazing, a traditional form of pastoralism, where the herd is supervised by a shepherd. This involves the animals returning after a certain period of time to areas previously grazed. This type of grazing is practised mainly in the mountains when grazing sheep and can be of great importance in naturally valuable areas as a factor stimulating the increase in their biodiversity and the preservation of naturally valuable areas [279].

While grazing strategies are fundamental, pasture composition also plays a vital role in determining forage nutrient density. Traditionally, pasture renovation has involved seeding grass–legume mixtures to ensure protein-rich animal feed. Legumes naturally fix N, reducing fertilizer dependency and improving protein content in forage. A more innovative approach is the integration of naturally occurring herbaceous species, leading to the development of multi-species pastures or herbal leys [197,198,199,201,280,281]. These diverse pastures enhance nutritional value, biodiversity, and drought resilience. Studies confirm that multi-species pastures can boost forage productivity by 25–40%, while herbal leys improve mineral balance and protein digestibility [180]. Key species improving forage quality are C. intybus, P. lanceolata, and A. millefolium. They improve mineral content [282] and boost livestock immunity.

6.6. Forage Preservations

Grazing and mowing are the primary methods of grassland utilization, with mown forage processed into hay or silage. To ensure high-quality hay, plants should be harvested at the optimal growth stage when their nutritional value is highest. Drying should be carried out under favourable weather conditions that help preserve high-quality protein and vitamins while preventing excessive drying or overheating. Proper drying time and storage techniques are essential for maintaining nutritional value and preventing mineral loss, and it is important to avoid issues such as mould growth, spontaneous heating, and reduced hygienic quality. To limit microbial growth in high-moisture hay (>20%), preservatives such as propionic acid, buffered organic acids, urea, anhydrous ammonia, and microbial inoculants are commonly applied [283]. Organic acid-based preservatives effectively reduce DM loss, mould development, bale temperature, and insoluble nitrogen while preserving sugars and DM digestibility. However, microbial inoculants have shown limited effectiveness in preventing hay spoilage, particularly in high-moisture conditions.

The production of high-quality silage depends on forage composition at ensiling and the application of proper preservation techniques. A key principle of successful silage-making is the rapid reduction in pH through lactic acid fermentation while maintaining anoxic conditions to inhibit spoilage [284]. Lactic acid bacteria play a crucial role in this process by converting fermentable carbohydrates into lactic and acetic acid. Chemical and biological additives can further enhance silage quality by accelerating pH reduction and preventing aerobic spoilage [285].

The primary goal of ensiling is to produce nutritious, sanitary, and stable feed while maximizing DM recovery despite variability in forage composition. Effective silage management minimizes DM losses, with wilting being a critical step in increasing DM content [286]. Forage should be cut using a mower conditioner and wilted in a wide swath to shorten field exposure, preserve soluble carbohydrates, and minimize effluent losses. Wilting before ensiling improves silage quality by increasing DM and water-soluble carbohydrate content while reducing DM losses, butyric acid formation, and ammonia levels. However, it does not significantly impact pH, CP levels, or in vitro DM digestibility [287].

Precise chopping enhances fermentation by releasing additional substrate and water from damaged cells [288]. Rapid packing to achieve the appropriate bulk density is essential, as porosity and DM content strongly influence silage quality, reducing aerobic degradation during feed-out [289]. Slow silo filling and delayed sealing compromise silage quality by promoting enterobacteria growth and heterolactic fermentation, leading to lower acetic acid concentrations. While complete elimination of fermentation losses is not possible, silage additives can significantly reduce them [285,290,291,292]. Lactic acid bacteria (LAB) inoculants enhance homolactic fermentation, reducing DM losses by minimizing CO₂ emissions during the initial fermentation phase [31]. Additionally, additives such as formic acid, selected LAB strains, and salt-based treatments improve fermentation quality under varying management conditions [293]. Collectively, these practices minimize losses and contribute to the production of high-quality silage.

6.7. Enhancing Forage Quality Through Smart Agriculture and Intelligent Grazing

The future of green forage improvement lies in Intelligent Grazing [294]. This emerging strategy leverages AI-driven livestock tracking, remote sensing, and precision grazing tools to enhance pasture productivity and forage quality. By integrating traditional grazing methods with real-time data analytics, farmers can implement more efficient, adaptive, and sustainable grazing systems. This approach relies on artificial intelligence, remote sensing, and automated systems to optimize pasture management. These technologies improve forage quality by preventing overgrazing through precision tracking, optimizing nutrient availability in pastures, and ensuring strategic grazing rotations to maximize biomass recovery. Innovations such as precision livestock tracking, automated rotational systems, and real-time pasture monitoring empower farmers to make data-driven grazing decisions, optimizing both forage efficiency and sustainability.

The core components of Intelligent Grazing include remote sensing, herd perception, guidance, and control. First, pasture remote sensing provides information on pasture quality based on canopy height and spectral characteristics of vegetation. A few-shot model is then used to classify biomass and pasture conditions [295]. Second, the remote sensing of livestock employs multi-source data-driven scene segmentation and hybrid-driven target-tracking algorithms to detect herd boundaries, identify stragglers and leaders, and guide UAVs (unmanned aerial vehicles) or efficient livestock monitoring [296]. Li et al. [297] proposed an autonomous barking UAV (unmanned aerial vehicle) to replace traditional herding methods, enabling rapid livestock gathering and controlled movement to designated locations.

Recent advancements in remote sensing technologies have greatly improved the accuracy of estimating plant quality, biomass, and yield [298,299,300]. The integration of satellite and drone technologies into precision agriculture is accelerating, driven by innovations in automation and data analytics. Zhu et al. [301] achieved an overall identification accuracy of 98.78% for grassland species using UAV-based hyperspectral imagery, with a kappa coefficient of 0.92, laying the foundation for high-precision grassland species detection.

Drones equipped with hyperspectral, multispectral, and RGB cameras have proven effective for vegetation monitoring [302]. Early approaches relied on vegetation indices and linear estimation for drone data analysis [303]. However, advanced machine learning techniques now incorporate structural features such as canopy height and plant texture, along with spectral characteristics like chlorophyll content and water absorption bands, from remote sensing datasets, enhancing correlations with reference measurements [304,305,306].

For instance, Dvorak et al. [307] utilized photogrammetric point clouds to estimate yield and nutritive value in alfalfa, including parameters such as ADF, NDF, and CP throughout its growth cycle. Similarly, Pontes et al. [263] developed UAV-based imaging spectroscopy models for CP and ADF across diverse grassland types. Askari et al. [308] demonstrated the potential of multispectral UAV imagery combined with partial least squares regression (PLSR) and multilinear regression (MLR) for predicting biomass and CP. Furthermore, Oliveira et al. [306] applied random forests (RF) and MLR to estimate fresh and dry biomass yields, along with forage quality parameters such as organic matter digestibility (D-value), NDF, indigestible neutral detergent fibre (iNDF), and WSC.

Advanced remote sensing techniques, combined with artificial neural network (ANN) analysis, enable precise modelling of pasture quality and optimisation of grazing management. ANNs are used to analyse large datasets collected from UAVs, hyperspectral sensors, and image analysis algorithms, allowing for the identification of key factors influencing forage quality and predicting its nutritional value. The application of ANNs also facilitates biomass growth modelling and the assessment of grassland digestibility under varying climatic conditions [63]. Sensitivity analysis within neural networks helps determine which variables—such as plant chemical composition, soil moisture, or grazing intensity—have the greatest impact on pasture productivity and regeneration capacity. By integrating ANN-based insights with real-time data from Intelligent Grazing systems, farmers can optimize grazing rotations, improve fertilization strategies, and enhance overall forage quality management.

Beyond grazing management, aerial seeding has emerged as an effective strategy for large-scale restoration of degraded grasslands. This method employs aircraft to broadcast seeds suited to local conditions, followed by enclosure and managed grazing prohibitions until vegetation is restored. Ma et al. [309] demonstrated that aerial seeding significantly enhances grassland restoration, providing valuable insights for future ecosystem management policies. Their findings support the implementation of targeted seeding programs in degraded areas, the development of region-specific seed mixtures to enhance biodiversity, and the integration of aerial seeding with grazing restrictions to ensure long-term vegetation recovery and soil stabilization.

7. Effects of Forage Quality Improvement

7.1. Improvement of Animal Performance and Welfare

Forage quality has a direct impact on animal performance. A comprehensive understanding of key forage quality traits is essential for enhancing ruminant productivity and welfare.

Table 1. Key forage traits affecting ruminant performance.

Forage Trait	Mechanism of Action	Effect on Animal Productivity	Reference
Crude protein	Supplies nitrogen for microbial protein synthesis	Supports milk yield, growth, reproduction	[310]
Fiber digestibility (e.g., NDFD, TTNDFD)	Determines rate of digestion and intake potential	Higher energy availability, improved milk and meat production	[40]
Water-soluble carbohydrates	Enhance microbial efficiency and rumen fermentation	Improved nutrient utilization, better nitrogen balance	[311]
Lignin content	Indigestible; binds to cellulose and hemicellulose	Reduces overall digestibility and intake potential	[312]
Fat content (PUFA, CLA)	Modifies rumen fermentation and milk fatty acid profile	Improves milk fat quality, can suppress methane, but may reduce fibre digestion if excessive	[313]
Mineral composition	Supplies essential macro- and microelements	Supports bone health, fertility, immune function; imbalance may limit productivity	[314]
Amino acid profile	Determines efficiency of absorbed protein use	Influences milk protein synthesis and muscle accretion	[315]
Anti-nutritional factors	Toxins or inhibitors affecting metabolism or intake	Reduced feed intake, digestibility, possible toxicity (e.g., alkaloids, tannins, mycotoxins)	[134]
Forage palatability	Influences voluntary feed intake	Determines actual nutrient consumption and grazing selectivity	[316]

summarizes the most critical forage parameters, their mechanisms of action, and their direct effects on animal performance.

High-quality forage, rich in essential nutrients such as proteins, carbohydrates, vitamins, and minerals, improves milk and meat production while supporting better reproductive outcomes.

One example of improving green forage is the introduction of T. repens into pasture swards. T. repens is highly digestible and provides substantial energy due to its low fibre content, resulting from a reduced proportion of structural components such as stems and sheaths. A key advantage of T. repens is its ability to maintain digestibility for a longer period during mid-season compared to perennial ryegrass. Increasing its proportion in swards has been shown to improve dairy cow performance. [317,318] demonstrated that cows grazing on swards containing over 20% T. repens produced higher milk yields and milk solids than those on grass-only swards. Studies conducted by [310] showed that dairy cows fed white clover silage consumed more dry matter (by 1.7–2.2 kg⁻¹ per day) and produced significantly more milk, on average 3.1 kg⁻¹ day more in one of the trials. The higher digestibility of organic matter and greater metabolizable energy content of white clover silage contributed to improved feed utilization. Moreover, despite the higher nitrogen content in the clover-based diet, a larger proportion of this nitrogen was efficiently converted into milk protein, confirming the superior nutritional value of this forage legume species.

The inclusion of plants rich in secondary metabolites, such as T. pratense, in silage offers multiple benefits, including improved production performance, health-promoting effects, and reduced environmental pollution, by enhancing digestive health, boosting immunity, reducing the risk of metabolic disorders, and supporting reproductive health in livestock. T. pratense silage progressively lowered protein degradation in the rumen, increased linearly ruminal escape of dietary protein, and decreased linearly microbial protein synthesis. Incremental inclusion of RCS in the diet tended to lower whole-body N balance, increased linearly the proportion of dietary N excreted in feces and urine, and decreased linearly the utilization of dietary N for milk protein synthesis [319]. Feeding cows T. pratense silage has been shown to enhance milk production [319,320,321], modify the milk fatty acid profile, and increase the content of cis-9, trans-11 conjugated linoleic acid (CLA), linoleic acid (C18:2n-6), and α-linolenic acid (C18:3n-3) [319]. A meta-analysis by [322] reported that increasing the dietary proportion of T. pratense silage linearly increased N intake but had no significant effect on dairy cow production, although an altered milk fatty acid profile was observed. The inclusion of T. pratense is also beneficial for meat quality. Luciano et al. [323] assessed the oxidative stability of meat from lambs fed T. pratense (silage and found that, while fresh meat stability remained unaffected, oxidative deterioration was reduced under strong pro-oxidant conditions.

Herbal leys, also known as multi-species swards, consisting of grasses, legumes, and forbs, are rapidly gaining popularity due to their beneficial effects on livestock productivity. Grazing on herbal leys has been linked to improved sward nutritional quality and increased DM intake. McCarthy et al. [324] observed that cows on multi-species pastures produced 1.20 kg more milk per day compared to those on conventional pastures, with significantly higher yields of energy-corrected milk, fat, protein, and total fat-protein content. Differences in milk composition likely stem from variations in nutrient availability in multi-species pastures [324]. The inclusion of C. intybus and plantain P. lanceolata in pasture diets has also been found to reduce rumination time and the number of chewing movements compared to L. perenne [325], indicating more efficient particle breakdown during ingestion, which minimizes the need for extended rumination and accelerates rumen emptying. This process facilitates higher feed intake, improving overall DM consumption [325,326]. However, these effects depend on the proportion of forbs in the pasture and the level of selective grazing by animals, as overgrazing of preferred species could reduce their persistence in swards. Cooledge et al. [327] reported that, while crude protein levels did not significantly increase in herbal leys, higher macro- and micronutrient concentrations were observed across both seasons. Spring liveweight gain in lambs grazing on herbal leys was 19.4% higher compared to those grazing on grass–clover leys, whereas no significant differences were observed in autumn. Spring-grazing lambs also exhibited elevated plasma cobalt and selenium, alongside lower blood urea levels. Furthermore, faecal egg (includes identified Moniezia, Nematodirus and Strongylids eggs) counts in spring were reduced by 78% in lambs grazing on herbal leys, whereas no significant differences were observed in autumn [327].

O’Donovan et al. [328] emphasized that selecting ryegrass cultivars with high digestibility and optimal sward structure is crucial for maximizing grazing efficiency and milk production. Structural traits play a key role in determining both herbage intake and milk yield. Wims et al. [329] demonstrated that cultivar-specific differences in sward structure, particularly the proportion of stems and stubble height (SH), significantly affect milk production, especially during the reproductive growth phase, when structural characteristics have a greater influence than chemical composition on forage utilization. Similarly, Gilliland et al. [330] reported that structural differences between cultivars directly impact grazing DM intake, often outweighing the effects of OMD in regulating total feed consumption and subsequent milk yield. Improved sward structure, characterized by reduced pseudostem content in the grazed horizon, has also been associated with increased milk yield [331].

Late-heading ryegrass cultivars have shown beneficial effects on milk production due to their superior chemical composition, maintaining higher digestibility over longer periods, which enhances forage intake and nutrient absorption. However, despite advancements in forage breeding, conflicting results exist regarding the benefits of cultivars with elevated WSC levels. While some studies suggest a positive effect on animal performance, others report minimal or inconsistent benefits, likely due to differences in experimental conditions, grazing management, or interactions with other dietary components [186].

Grazing management systems, including rotational and continuous strategies, are central to the functioning of permanent grasslands and significantly influence forage quality. Therefore, these systems are comprehensively discussed in Section 6.5. While pasture composition plays a crucial role in forage quality, its full potential can only be realized through effective grazing strategies. Therefore, a Grazing Management Plan (GMP), a structured framework designed to ensure sustainable pasture use by balancing livestock stocking rates with the land’s carrying capacity, is helpful. A well-designed GMP incorporates several key components, including adjusting grazing intensity to prevent overgrazing and soil degradation, implementing rotational grazing to allow pastures sufficient recovery time, and monitoring soil fertility to maintain high-quality, nutrient-rich forage throughout the grazing season. By preventing overgrazing and ensuring optimal rest periods, GMP enhances forage digestibility, crude protein content, and overall plant resilience. Research by [25] found that a five-year GMP implementation in sub-alpine and alpine pastures led to more efficient forage utilization, increased biomass production, and improved livestock performance. These findings emphasize the importance of structured grazing plans in optimizing pasture sustainability and animal nutrition.

7.2. Environment Protection

Feeding ruminants high-quality forages can significantly reduce greenhouse gas (GHG) emissions from livestock. The primary determinants of forage quality are the growth stage at harvest and the species composition of the sward. As forage matures, its fibre content increases, especially cellulose and lignin, which reduce digestibility and prolong rumen fermentation, leading to greater methane (CH₄) production by methanogenic archaea. However, including forage legumes in ruminant diets can mitigate GHG emissions by reducing the need for synthetic N fertilizers, enhancing biodiversity, and decreasing parasitism in livestock. Flavanol monomers and condensed tannins in legume plants are effective in vitro against parasitic nematodes from sheep, goats, cattle, deer, and other species [332]. Condensed tannins are thought to act directly against the parasites, because of their ability to form strong complexes with proline-rich proteins, which are present on nematode surfaces [333]. These benefits make legume-based pastures both environmentally and economically advantageous in systems where nitrogen inputs are not excessive [334].

In addition to the benefits of forage legumes, adjusting the timing of grass harvesting is another effective strategy to mitigate environmental impact. Warner et al. [335] demonstrated that harvesting grass silage at an earlier growth stage significantly reduces enteric CH₄ emissions in dairy cows, independent of DM intake. However, earlier cutting was also associated with increased nitrogen losses from manure. These findings confirm that methane emissions from dairy cows depend not only on feed intake levels but also on the nutritive value and chemical composition of the forage.

The inclusion of T. repens in L. perenne swards has been shown to lower the environmental footprint of intensive pasture-based dairy systems at a given stocking rate [336]. Replacing carbon-intensive synthetic N fertilizers with biologically fixed N from T. repens (reduced emissions of N₂O, CO₂, and NH₃, as well as nitrate (NO₃⁻) leaching. Moreover, improved animal performance associated with WC led to greater milk yields, thereby diluting emissions per unit of production. This reduced the environmental impact both per hectare and per metric tonne of fat- and protein-corrected milk, emphasizing the role of feed efficiency in sustainable dairy systems.

7.3. Reduction of Production Costs

Improved forage quality enables animals to achieve higher performance with lower feed intake, leading to reduced overall production costs. Higher digestibility ensures that less feed is wasted, allowing more nutrients to be effectively utilized.

For example, incorporating Trifolium species into grazed grass swards has been shown to enhance both productivity and profitability compared to grass-only systems in sheep and dairy production [318]. In the southeastern USA, introducing more persistent T. repens into pastures resulted in an additional US $86 ha⁻¹, driven by increased cattle liveweight gain and reduced nitrogen fertilizer requirements [337]. Similarly, in New Zealand, the annual economic contribution of T. repens, considering nitrogen fixation, forage yield, seed production, and honey production, was estimated at NZ $3.095 billion [338].

8. Directions of Future Study

Shaping forage quality from permanent grasslands is a crucial research area that requires an interdisciplinary and practical approach. Contemporary challenges such as climate change, the need for more efficient agricultural production, and environmental protection are driving scientists to seek new solutions. One of the key research directions is the adaptation of grassland communities to changing weather conditions. This includes developing new varieties of grasses and legumes that are more resistant to increasingly observed in Europe drought, high temperatures, or soil salinity.

Improving the botanical composition of meadows and pastures remains a priority. Current research focuses on increasing the share of leguminous species, such as T. repens, T. pratense, and L. corniculatus which enrich forage with protein and improve its digestibility. The selection of suitable species in seed mixtures for grassland depends on the soil conditions, moisture content, and intensity of use. Grass species with lower nitrogen requirements should be selected for extensively used grassland. In addition, they should include leguminous plants that will fix nitrogen from the air. Scientists are also refining multi-species mixtures to achieve better nutritional value with maintaining the productivity of grasslands. At the same time, strategies for controlling undesirable plant species, including toxic or low-value weeds that may reduce forage quality and pose risks to animal health, are also being explored.

Another important research area is the development of modern fertilization methods and improving soil fertility. Precision fertilization, using GPS technology and soil nutrient maps, makes it possible to tailor fertilizer doses to the actual plant needs. Researchers are also investigating biostimulants and biofertilizers, including PGPB for their potential to boost on forage quality and nutritional value.

A grazing method that has great potential for development and dissemination is virtual fencing. Although its application is already well-documented in cattle systems, more studies are needed, especially regarding its use with sheep. Virtual fencing may help address problems such as undergrazing and enable more precise control over where and how animals graze.

Equally important is the further optimization of forage harvesting and preservation methods. In this context, innovative silage additives are being analysed to improve the fermentation process, prevent the development of undesirable microorganisms, and enhance forage digestibility.

Modern technologies are also playing a growing role in monitoring forage quality, for example, NIRS for rapid and precise nutritional analysis directly in the field. Intelligent systems based on sensors and artificial intelligence are also being tested, enabling continuous monitoring of the chemical composition of forage and detecting potential contaminants such as mycotoxins.

Another crucial research direction is the impact of forage quality on animal health and productivity. New feeding strategies are being developed to better match forage composition to the metabolic needs of ruminants, aiming for higher milk and meat yields.

At the same time, studies are exploring how to reduce methane emissions from livestock through appropriate dietary modifications based on forage from permanent grasslands. While this review focuses primarily on temperate grasslands in Europe, it is important to note that grasslands in tropical or arid regions have different ecological conditions and management needs. Including examples from such areas in future studies would help tailor solutions to a wider range of climatic and socio-economic contexts.

9. Conclusions

Improving the quality of forage from permanent grasslands is essential to increase ruminant productivity and make efficient use of biomass as a high-value feed source. In the context of climate change and growing demands for sustainable animal production, the development of well-adapted, productive, and diverse grassland systems is becoming increasingly important.

This review highlights both breeding and management strategies that contribute to improved forage quality. Selective breeding of grasses and legumes has proven effective in enhancing digestibility, stress resistance, and nutritional value. Agronomic practices, such as sward renovation, precise fertilization, optimized harvest timing, rotational grazing, and the use of appropriate conservation techniques, also play a key role.

Based on the reviewed literature, we identify the following as the most impactful strategies for improving forage quality in temperate permanent grasslands:

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Breeding and selection of grass and legume cultivars with enhanced digestibility, reduced fibre fractions, and greater tolerance to environmental stress.

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Optimization of mowing and grazing regimes to balance yield, forage quality, and long-term sward persistence.

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Diversification of sward composition, including legumes and functional forbs, to boost protein content, palatability, and mineral availability.

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Targeted fertilization and soil management that maintain nutrient supply while preserving forage quality.

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Effective weed control and sward renovation to ensure dominance of productive and palatable species.

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Use of precision technologies for real-time monitoring, assessment, and management of forage systems.

Nevertheless, the practical implementation of these innovative strategies may be constrained by economic factors, infrastructure limitations, and varying levels of farmer acceptance, which should be carefully considered in future research and policy development.

Future research should focus on tailoring these strategies to local agroecological conditions and improving their economic viability and acceptance among farmers. Integrating innovation with traditional knowledge will be key to unlocking the full potential of permanent grasslands.