Silage Preparation, Processing and Efficient Utilization

Ensiling is a technique for the long-term preservation of feed which is both effective and widespread, and it is characterized by low costs and ease of operation [1]. At the initial stage of ensiling, water-soluble carbohydrates (WSCs) are broken down into carbon dioxide, water and energy under the respiration of aerobic bacteria. As oxygen is depleted, lactic acid bacteria (LAB) attached to forage multiply and convert WSCs into organic acids, thereby creating an anaerobic and acidic environment, which in turn inhibits the activities of undesirable bacteria, such as clostridia, and reduces the risk of forage spoilage [2]. Ensilage is a complicated process involving the actions of microbes and biochemical variations. It is one of the most significant methods of preserving herbages [3]. Animals that consume silage have been shown to enhance the bioavailability of animal protein and decrease methane emissions [4]. A plethora of silage resources are available on Earth. However, the utilization rates remain low, resulting in significant resource wastage and substantial environmental degradation. Conversely, the accelerated growth in animal production has resulted in a persistent annual deficit of animal roughage. Consequently, it is now imperative to investigate the current state of silage preparation, processing and efficient utilization. The Special Issue, entitled “Silage Preparation, Processing and Efficient Utilization”, comprises 11 original research articles. Collectively, these contributions illustrate the promising future of silage application, with the objective of advancing the frontiers of animal feed.

The scarcity of quality roughage resources is the primary factor hindering the advancement of the sheep industry in numerous developing countries. In China, southern Xinjiang is distinguished by its extensive saline soil and desertification areas, characterized by minimal natural rainfall and infertile soil. Consequently, the availability of quality roughage resources in this region is notably limited. Sweet sorghum (SS) has been identified as a promising forage, capable of thriving in high salinity, semi-arid and arid environments. Licorice (LC) has been characterized as a drought-tolerant, saline-resistant perennial leguminous herbage. In this study, Chen et al. (contribution 1) evaluated the ensiling characteristics, fermentative products, in vitro digestibility, aerobic stability and ruminal degradation characteristics of silage mixtures with various proportions of SS and aerial sections of LC. The ensiling of SS and LC mixtures was found to enhance silage quality, particularly at a ratio of 50:50 on a dry matter basis.

The most effective ensilage practice is wilting in the field. This process has been shown to reduce ensilage effluent, decrease proteolysis and respiration, increase the levels of WSC as a fermentative substrate and favor LAB over clostridia and enterobacteria, thereby reducing the production of butyric acids under anaerobic conditions. It is imperative that the LAB strains not only survive, but also perform under enhanced osmotic pressure during ensiling, a process that arises from the optimal wilting of forage. Consequently, simple laboratory protocols are needed to isolate suitable LAB strains as bacterial additives for high-dry-matter (DM) forages. Martens et al. (contribution 2) simulated a high-osmolality environment without inducing salt stress to choose an appropriate indicator of LAB performance. Finally, the developed liquid growth medium was shown to approximate high-DM conditions, thereby enabling the selection of osmotolerant homofermentative LAB strains.

Following the opening of a silo, the silage within is susceptible to a range of challenges, including contamination, rot and aerobic deterioration. Biocontrol bacteria, defined as a type of biological antiseptic, have been shown to be highly natural and effective. Zhang et al. (contribution 3) screened a strain named D-2, which demonstrated anti-microbial activity against silage spoilage microorganisms. The study examined the effects of this strain on the fermentative profile, in vitro digestion and gas production and aerobic stability of ensilage. The D-2 strain was isolated from rotten whole-crop corn ensilage and identified as Bacillus velezensis. Overall, the D-2 strain has been shown to possess a high level of resistance to both rot-causing and pathogenic microbes, thereby facilitating its adaptation to the conditions prevalent in ensilage. Furthermore, it has been demonstrated to enhance aerobic stability and mitigate the loss of nutritive value in ensilage, suggesting potential methods in the prevention of ensilage rot and greenhouse gas production.

In Brazil, corn (Zea mays L.) is the most widely cultivated crop for ensilage production. This is due to its high productivity, high energy content, good nutritive value, ease of fermentation inside the silo and good palatability for most ruminants. However, environmental conditions vary significantly among cultivation regions and directly affect the qualitative and productive performance of this forage, resulting in alterations in the quality and yield of the ensilage. Consequently, Neumann et al. (contribution 4) undertook an evaluation of the chemical–bromatological composition of 498 samples of corn silage from mesoregions in Southern Brazil during the 2022/2023 summer harvest. The study revealed that the silages from the Southwest-PR and West-SC regions exhibited higher ratios of rapidly degrading substrates and superior nutritive value. In contrast, the silages from the Central South-PR region demonstrated greater energy levels, while those from the North-PR, Northwest-RS and West-PR regions exhibited higher levels of low-digestible fibers and lower nutritional value.

The utilization of total mixed rations (TMRs) in the production of animal feeds has become a prevalent practice, enabling the provision of nutritionally balanced diets and a reduction in feed selection by animals. Monensin (MON) and essential oils (ELO) have been shown to possess antimicrobial characteristics that could affect the fermentative profile. In their research, de Andrade et al. (contribution 5) assessed the effects of using ELO and MON on the quality of the TMR ensilage process and identified the primary changes in TMR fermentation at various moisture levels. The study concluded that the strategic utilization of ELO and MON might effectively enhance the TMR fermentation quality by promoting acid production and improving aerobic stability and could benefit ruminants. The study proved that ELO interacts with the ensilage moisture level and affects its impact on ensiling characteristics. Consequently, when the DM level of silages exceeds 40%, it is advised to administer a greater dose (ELO600, 600 mg of essential limonene oil per kg of DM), and for TMR silages with a DM level below 30%, a lower dose (ELO300, 300 mg of essential limonene oil per kg of DM) is recommended.

Millet (Setaria italica) is one of the most significant crops in the world, and it is notable for its low water needs compared to other cereal crops and its ability to thrive in poor soils. Millet is characterized by its high nutritional content, specifically its abundance of crude protein and fiber, which renders it a highly suitable feedstock. However, its high moisture level could pose significant challenges during storage, and the process of producing quality whole-crop millet ensilage is intricate due to the impacts of multiple factors. Zhao et al. (contribution 6) investigated the effects of varying growth stages (harvested at different stages) and the incorporation of Lactiplantibacillus plantarum and soluble carbohydrates on the fermentative profiles and bacterial communities of whole-plant millet. The results suggested that the dough stage possessed the greatest WSC and crude protein levels. The dough stage was found to have higher lactic acid and crude protein contents than other stages, and the lowest pH was recorded during this stage. The study concluded with the recommendation that millet should be harvested at the dough stage and that the addition of a mixture of sugar and Lactiplantibacillus plantarum should be made to enhance ensilage quality and aerobic stability.

It is imperative for dairy producers to understand the influences of adding enzyme and bacteria on mixed ensilage to make informed decisions. Ramie (Boehmeria nivea L. Gaud.) is a non-conventional fiber plant that is applied as animal feed due to its important nutritive value. It is cultivated in numerous regions worldwide. Li et al. (contribution 7) assessed the chemical variations in ensilage prepared from various elephant grass and ramie proportions in response to enzyme and bacteria additives. The best-quality ensilage was found when the proportion of elephant grass to ramie was 70:30 and the doses of compound enzyme and bacteria and enzyme were 20 mg/kg and 200 mg/kg, respectively. The results indicated that fermentative products are influenced by forage ratios/types, while enzymes and bacteria interact not only with each other but also with forage types to influence the compositions of mixed ensilage prepared from elephant grass and ramie.

The ensiling of biomass from poplar and willow harvested for feeds in the growth season has been demonstrated as a viable method of preservation; however, the extent of research conducted on this subject is limited. Larsen et al. (contribution 8) focused on storing green tree biomass collected from poplar and willow in the growth season by ensilage, i.e., via decreasing the pH to a low value of about 4.0. The laboratory-scale ensilage experiments indicate that the pH is usually not decreased sufficiently in poplar and willow biomass during ensilage without the application of a feed additive. However, a low pH value could be observed in willow biomass by adding a dose of 2–5 kg per tonne of fresh weight (FW) of formic acid (78%) or by applying molasses and/or LAB, which could ensure an adequate and rapid pH decrease. In the case of poplar biomass, LAB and molasses appear to be less effective, while formic acid seems to be a more effective silage additive. This research provides comprehensive guidelines for ensuring a low pH during the ensilage of poplar and willow biomass.

Ensiling high-moisture herbage poses a considerable challenge in obtaining good fermentation, because the ensilage process is susceptible to butyric acid fermentation and nutrition loss. The most effective method of lowering the moisture content of herbage is field wilting. However, harvesting herbage is not without its challenges, particularly in rainy and wet regions. Consequently, farmers may be obliged to harvest herbage and produce ensilage when its moisture level is high. Italian ryegrass (Lolium multiflorum Lam.) is an extensively planted herbage with good palatability and high amounts of yield for livestock, and it flourishes during the spring and winter months. As a high-energy grass, it is well suited for the feeds of ruminants, and it could be utilized as fresh grass, hay or ensilage. Nevertheless, research on high-moisture Italian ryegrass ensilage is scarce. Thus, Wang et al. (contribution 9) assessed the fermentative profiles, bacterial communities, co-occurrence networks and their functional shifts and pathogenic risks in high-moisture Italian ryegrass (IR) ensilage. The results indicated that the fermentation process decreased the complexity of the bacterial networks in IR ensilage. The metabolism of amino acid and carbohydrate was limited during the initial stage of fermentation. In addition, 1-phosphofructokinase and pyruvate kinase were important in accelerating the lactic acid production. A higher proportion in the “potentially pathogenic” category was observed in the bacterial communities of IR ensilage than in fresh IR. It was concluded that the high-moisture IR ensilage performed well in terms of fermentation quality, whereas risks for bacterial contamination and pathogens existed after fermentation.

Alfalfa (Medicago sativa L.) is the most extensively planted legume globally, with an estimated production of about 450 million tons across 30 million hectares. In recent years, alfalfa production in China has been increasing annually, with 546,700 hectares being cultivated in 2020. Nevertheless, clostridial fermentation remains the predominant process responsible for the deterioration of direct-cut alfalfa silage. In response to this challenge, LAB inoculants are often applied to promote lactic acid fermentation, because other technical ways show some inevitable defects. In this study, Zheng et al. (contribution 10) screened target-based LAB strains and identified and correlated the key Clostridia and LAB species in alfalfa silage. The study concluded that Enterococcus faecalis, Lentilactobacillus buchneri and Lactiplantibacillus pentosus could be utilized as potential LAB inoculants for the targeted inhibition of clostridial fermentation. This study has enhanced our comprehension of the clostridial fermentation mechanism of ensilage and may be instrumental in the isolation of target-based LAB additives to produce quality alfalfa ensilage.

Oat (Avena sativa L.) is regarded as a major food crop and feed resource on a global scale. It is abundant in vitamins, dietary fiber, carbohydrates, quality protein and minerals, thus rendering it an optimal selection for livestock feeds. Nevertheless, the seasonal nature of oat production can lead to fluctuations in the consistent year-round supply of herbage, and insufficient storage methods result in enormous losses of fresh herbage. To address this challenge, Huang et al. (contribution 11) investigated the impact of biological additives, namely Bacillus subtilis (BS), xylanase (XT), Streptococcus bovis (SB) and their combinations, on the fermentative products and microbial community of high-moisture oat ensilage. In comparison with the control (no additives), the SB and SBBS groups promoted the lactic acid production and decreased the levels of propionic acid, acetic acid, ammonia nitrogen and butyric acid in ensilage. In contrast, the XT, SBXT and BSXT treatments resulted in a decrease in acid and neutral detergent fiber contents, accompanied by an enhancement in WSC level. The conclusion drawn was that adding SBBS and SB helps to improve the silage quality of forage oat, but BSXT, SBXT and XT performed superiorly in degrading lignocellulose of herbage.

This Special Issue comprises a series of original studies in the field of silage, including research on the exploration of silage additives and novel raw materials, the utilization of co-ensiling technology, the investigation of microbial community structure and pathogenic risks and associated subjects. The findings of these studies contribute to the increase in ensilage raw materials and improvements in silage fermentation quality. Future research should focus on studying microbial interactions, metabolites and the identification and construction of core microorganisms during ensiling and aerobic exposure.