Natural Feed Additives in Sub-Saharan Africa: A Systematic Review of Efficiency and Sustainability in Ruminant Production

Simple Summary

In recent years, there has been a growing interest in utilising natural feed additives as a promising strategy to enhance the efficiency and sustainability of ruminant livestock production, particularly in addressing persistent challenges within the sector. The objective of this systematic review was to critically assess the effectiveness and sustainability of natural feed additives in ruminant livestock production across Sub-Saharan Africa. The literature search was conducted in accordance with PRISMA guidelines, utilising major academic databases such as Scopus, ScienceDirect, Web of Science, and EBSCOhost, covering the period from 1 January 2000 to 31 December 2024.

Abstract

Ruminant livestock production plays a crucial role in the agricultural systems of Sub-Saharan Africa, significantly supporting rural livelihoods through income generation, improved nutrition, and employment opportunities. Despite its importance, the sector continues to face substantial challenges, such as low feed quality, seasonal feed shortages, and climate-related stresses, all of which limit productivity and sustainability. Considering these challenges, the adoption of natural feed additives has emerged as a promising strategy to enhance animal performance, optimise nutrient utilisation, and mitigate environmental impacts, including the reduction of enteric methane emissions. This review underscores the significant potential of natural feed additives such as plant extracts, essential oils, probiotics, and mineral-based supplements such as fossil shell flour as sustainable alternatives to conventional growth promoters in ruminant production systems across the region. All available documented evidence on the topic from 2000 to 2024 was collated and synthesised through standardised methods of systematic review protocol—PRISMA. Out of 319 research papers downloaded, six were included and analysed directly or indirectly in this study. The results show that the addition of feed additives to ruminant diets in all the studies reviewed significantly (p < 0.05) improved growth parameters such as average daily growth (ADG), feed intake, and feed conversion ratio (FCR) compared to the control group. However, no significant (p > 0.05) effect was found on cold carcass weight (CCW), meat percentage, fat percentage, bone percentage, or intramuscular fat (IMF%) compared to the control. The available evidence indicates that these additives can provide tangible benefits, including improved growth performance, better feed efficiency, enhanced immune responses, and superior meat quality, while also supporting environmental sustainability by reducing nitrogen excretion and decreasing dependence on antimicrobial agents.

1. Introduction

Ruminant livestock production continues to serve as a critical element within agricultural systems across Sub-Saharan Africa (SSA), providing income and employment opportunities for smallholder farmers, acting as a source of nutritional food products, and serving as a financial buffer that enhances economic stability in rural households [1,2]. This sector encompasses a wide range of farming practices involving cattle, sheep, and goats, which collectively produce essential products such as meat, milk, and manure [1,3]. It serves as a significant source of income for both commercial and local farmers throughout the Sub-Saharan African region, and it not only generates direct income through the sale of animals and animal products but also creates employment opportunities across the production, processing, and marketing value chains [4,5,6]. In this manner, the sector contributes significantly to poverty alleviation, gender empowerment, and the overall resilience of rural communities. Consequently, ruminant production plays a significant role in supporting the livelihoods of millions of smallholder farmers across Sub-Saharan Africa. Dhne [7]. Despite its critical importance, the productivity of ruminant livestock in Sub-Saharan Africa is hindered by numerous challenges, foremost among them being the poor quality and seasonal scarcity of feed resources, elevated feed costs, and climate-related stresses [7,8]. These constraints frequently lead to diminished animal performance and reduced efficiency, thereby undermining the sustainability and profitability of livestock farming within the region.

In recent years, the application of natural feed additives has garnered growing interest as a promising strategy to address challenges in livestock production by enhancing both the efficiency and sustainability of ruminant production [9,10,11]. Sustainability, as defined by the Brundtland Commission, refers to meeting present needs without compromising the ability of future generations to meet theirs, emphasising intergenerational equity [12]. The Food and Agriculture Organisation [13] frames sustainability through three interrelated pillars that include environmental, social, and economic sustainability. Natural feed additives are derived from biological sources such as plants, algae, fungi, and microbial cultures [14]. Unlike synthetic growth promoters, which are increasingly subject to regulatory restrictions due to health and environmental concerns, natural additives are considered safer alternatives [9,15]. These substances have been shown in various studies to enhance feed palatability and intake, improve nutrient digestibility, support immune function, and stimulate growth and reproductive performance in ruminants [16,17,18]. Notably, some natural additives also possess antimicrobial and anti-methanogenic properties, enabling them to reduce enteric methane emissions, a significant source of greenhouse gases from livestock, and thereby contribute to the mitigation of climate change [19,20]. However, the adoption of natural feed additives in sub-Saharan Africa faces several significant challenges. These include the absence of robust local production and supply chains, which drive up costs and create erratic availability [1].

Furthermore, technical knowledge gaps among farmers and feed formulators regarding their appropriate application and advantages are prevalent [21]. The approval and market access of these additives are also constrained by underdeveloped regulatory frameworks and a lack of standardisation [7]. Finally, socio-economic factors such as market reluctance, constrained purchasing power, and preference for conventional options act as additional impediments to broad implementation [22].

Globally, there has been a growing interest in natural feed additives as producers increasingly seek alternatives to synthetic growth promoters, particularly in light of escalating regulatory restrictions on the use of antibiotics in livestock production [9,14,23]. However, despite the expanding global body of literature, studies specifically addressing the efficacy and contextual relevance of natural feed additives within Sub-Saharan Africa remain relatively limited [24]. Considering the region’s diverse agroecological zones, indigenous livestock breeds, and unique feeding practices, evidence derived from other regions may not be directly transferable or applicable [25]. Despite the growing global interest in natural feed additives, there remains a notable gap in evidence synthesis in SSA. Many questions remain regarding the efficacy, economic feasibility, and practical integration of these additives within local production systems. To bridge this gap and inform evidence-based policymaking and innovation, there is a critical need for a comprehensive evaluation of available literature focused specifically on the SSA context.

The objective of this systematic review is to critically evaluate the efficiency and sustainability of natural feed additives in ruminant livestock production across Sub-Saharan Africa. Specifically, the review aims to synthesise and consolidate existing evidence regarding the effects of plant-based and naturally derived feed additives on key performance indicators, including animal growth, milk production, conversion efficiency, health parameters, nutrient utilisation, and environmental outcomes such as methane emissions. Moreover, it seeks to assess the potential of these additives to function as viable, locally adapted alternatives to synthetic growth promoters within the framework of sustainable and resilient ruminant livestock development tailored to the unique needs and realities of the region.

2. Materials and Methods

The literature search was conducted per the PRISMA guidelines [26]. A systematic literature search was conducted in academic databases, including Scopus, ScienceDirect, Web of Science, and EBSCOhost (Academic Search Ultimate), covering the period from 1 January 2000 to 31 December 2024, as shown in

Table 1. Specific search terms used for each database.

Database	Search Terms (String)	Filters Applied
Scopus	(“natural feed additives” OR “plant additives” OR “plant-based additives”) AND (“ruminant” OR “cattle” OR “sheep” OR “goats”)	Document Type: Article; Language: English
Web of Science
ScienceDirect
EBSCOhost (Academic Search Ultimate)

. After sorting the results by literature type, the following categories were excluded from the analysis: revisions, books, short communications, congress papers, review articles, and letters. Also, only studies published in English were included. The reason for this includes the dominance of English in scientific publishing, search term efficacy, database coverage, and resource constraints (time, cost, and expertise). The articles retrieved from each database were exported and subsequently imported into EndNote. Within EndNote, all records were organised into a single group. Following this, the articles were exported from EndNote and imported into Covidence for title and abstract screening, as well as full-text review.

2.1. Inclusion and Exclusion Criteria

Studies were considered eligible for inclusion if they met the following criteria:

• Studies involving ruminant animals.
• Use of natural feed additives, such as plant extracts, herbs, essential oils, organic acids, probiotics, enzymes, clay, seaweed, or tannins.
• Only additives derived from natural sources were considered.
• Studies reporting on production efficiency outcomes.
• Studies reporting on sustainability indicators.
• Research conducted within countries in Sub-Saharan Africa
• Studies published in English
• Originally published research articles
• Studies were excluded based on the following criteria:
• Studies focusing on non-ruminant species.
• Research conducted outside Sub-Saharan Africa.
• Use of synthetic or chemical feed additives, such as antibiotics, synthetic vitamins, or hormonal growth promoters.
• Studies where the nature of the additive cannot be determined or is not natural.
• Studies not reporting on production efficiency or sustainability-related outcomes.
• Nutritional composition or feed formulation studies without animal performance data.
• Revisions, books, short communications, congress papers, review articles, and letters.

2.2. Assessment of Risk of Bias

Two members independently evaluated the quality, validity, and possible bias risks of the included studies by applying the risk of bias tool for animal research developed by the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE). This assessment covered key bias categories such as selection bias (including random sequence generation, baseline comparability, and allocation concealment), performance bias (random housing and caregiver blinding), detection bias (random outcome assessment and blinding of outcome evaluators), attrition bias (handling of incomplete outcome data), and reporting bias (selective outcome reporting), as well as any other potential bias sources.

3. Results

3.1. Characteristics of the Included Studies

The outcomes of the systematic search are presented in Figure 1. A total of 319 records were retrieved from the following databases: Scopus (57 records), ScienceDirect (191 records), Web of Science (40 records), and EBSCOhost (31 records). Following the removal of 48 duplicate records by Covidence and title/abstract screening, 175 studies were excluded. Full-text screening was performed on 64 articles, with 58 excluded according to eligibility criteria. Six studies were included in the final review, and all six studies were conducted within Sub-Saharan Africa.

3.2. Synthesised Findings

This systematic review aims to evaluate the efficiency and sustainability of natural feed additives in ruminant livestock production systems across Sub-Saharan Africa. Within the scope of the included literature, fossil shell flour (FSF) was the most extensively investigated additive, accounting for 50% of the reviewed articles. All studies involving FSF were conducted on Dohne Merino sheep, consistently demonstrating dose-dependent improvements in feed intake, average daily gain (ADG), and feed efficiency [27,28,29]. Optimal responses were generally observed at moderate FSF inclusion levels, ranging from 40 to 60 g/kg of feed [28,29]. The other included studies explored other phytogenic or microbial additives, specifically Azadirachta indica and Moringa oleifera leaf extracts in sheep [30], Curcuma longa (turmeric) in West African Dwarf goats [31], and a combination of probiotics and essential oils in Bonsmara cattle [32]. Across the diverse species examined, natural feed additives generally evinced an improvement in at least one key performance trait, with observed variations attributable to species, additive type, and specific inclusion strategies.

Refs. [27,28,29] comprehensively investigated the inclusion of fossil shell flour in the diets of Dohne Merino wethers and rams as feed additives. These studies consistently reported improvements in growth performance, water intake, digestibility, nitrogen retention, heat tolerance, and feed preference. For instance, ref. [27] observed that an optimal FSF inclusion (4%) of DM led to a significant increase in ADG from 84.7 g/d (control) to 121.4 g/d (p < 0.000), representing a 43.3% increase. This dosage also improved feed efficiency from 0.14 to 0.19 (p < 0.011), indicating a substantial 35.7% improvement in FCR. Similarly, ref. [29] reported that FSF significantly improved ADG from 79.55 g/d (control) to 122.08 g/d at 60 g FSF/kg inclusion (p < 0.001), a 53.5% increase, alongside an FCR improvement from 0.16 to 0.21 (p < 0.01), marking a 31.3% improvement, as shown in

Table 2. Summary of natural feed additives used in the included studies.

Study (Author, Year)	Country	Study Design	Animal Type	Sample Size	Intervention (Type and Dose)	Comparator	Duration	Purpose	Key Outcomes	Main Findings
Omotoso et al. (2022) [31]	Nigeria	CRD	WAD doe goats	20	Curcuma longa (10 g TRP/day)	Concentrated diet	56 days	Enhance nutrient intake, growth, and rumen fermentation	↑ ADG, ↓ FCR, ↑ feed intake	Daily turmeric dosing improved performance; intermittent dosing was less effective
Webb et al. (2022) [30]	South Africa	CRBD	Dohne Merino wether lambs	40	A. indica and M. oleifera leaf extracts (50 mg/kg feed)	Monensin	23 weeks	Improve carcass quality and FA profile	No significant effect on carcass traits (p > 0.05)	Moringa showed numerically leaner carcasses; no statistical difference was observed
Linde et al. (2023) [32]		CRD	Bonsmara weaners	48	Probiotic (2.75 g/d), EO (3.21 g/d), monensin (0.3 g/d)		120 days	Modify rumen microbiome and improve feed efficiency	↔ ADG, ↔ DFI, ↓ FCR (PRO vs. MON)	PRO and EO matched monensin for growth, with PRO showing superior FCR (p < 0.05)
Ikusika et al. (2019) [27]			Dohne-Merino wethers	16	FSF at 0%, 2%, 4%, and 6% of DM	40:60 concentrate: hay	105 days	Assess growth, digestibility, and N retention	↑ feed intake, ↑ ADG, ↓ FCR, ↓ water intake	FSF improved growth and efficiency dose-dependently; 4% was most effective
Mwanda et al. (2020) [28]			Dohne Merino rams	24	FSF at 0, 20, 40, 60 g/kg		100 days	Improve heat tolerance and stress resistance	↑ weight gain, ↑ feed efficiency, ↑ water intake	40–60 g/kg FSF improved growth and stress resilience under heat
Ikusika & Mpendulo (2023) [29]			Dohne Merino rams		FSF at 0, 20, 40, 60 g/kg		90 days	Evaluate feed preference, growth, and BCS	↑ intake, ↑ BCS, ↑ preference score	60 g/kg FSF is most preferred; improved BCS and performance

CRBD: Completely randomised block design; CRD: Completely randomised design. The ↔ symbol means there was no significant change or no effect, while the ↓ symbol means there was a decrease and the ↑ symbol means there was an increase.

. These consistent and significant improvements across various physiological parameters highlight the robust responsiveness of Dohne Merino sheep to FSF supplementation. Figure 2 shows the geographic location in the map of Africa where these studies contain in Table 2 were conducted. It could be seen from Figure 2 that Most studies (n = 4) were conducted in South Africa, while only one study originated from Nigeria.

In feedlot cattle, ref. [32] investigated the effect of a Bacillus probiotic and essential oils (PRO/EO) compared to an ionophore (monensin) in Bonsmara weaners. While the study’s primary focus was the rumen microbiome, significant performance data were also reported. The PRO/EO group (EO) achieved an FCR of 6.91, which was numerically higher (inferior) than the control (CON: 6.25), monensin (MON: 6.25), and probiotic (PRO: 6.24) groups, though the difference was not statistically significant (p = 0.255). The ADG of the PRO group was 1.70 kg/day, which was numerically lower but not significantly different from the monensin group (1.85 kg/day), and the EO group had an ADG of 1.68 kg/day, significantly lower than the MON group (p < 0.05). This suggests that while these additives may modulate the rumen microbiome, their direct impact on FCR and ADG, when compared to monensin, showed limited variation or even inferiority in this study.

For the West African Dwarf breed of doe goats, ref. [31] found that Curcuma longa supplementation at varying feeding frequencies (control, once a week, alternate days) did not significantly improve daily weight gain or feed conversion ratio. The daily weight gain ranged from 48.22 to 51.79 g/d, and FCR from 10.50 to 10.86, with no significant differences among groups. This indicates a limited or no effect of Curcuma longa on growth performance and FCR in these goats under the tested conditions.

Lastly, ref. [30] investigated Azadirachta indica and Moringa oleifera leaf extracts in South African Mutton Merino lambs, as shown in

Table 3. Natural feed additives used in included studies: Reported effects on ruminant livestock and recommended inclusion levels.

Natural Feed Additive	Ruminant Livestock	Recommended Dosage	The Effect of Natural Feed Additives	References
Fossil shell flour	Dohne-Merino wethers	Inclusion of FSF at 4% of DM	Improvements were in dry matter intake (DMI), feed efficiency, average daily gain, total weight gain, nitrogen retention, and the apparent digestibility of most nutrients	Ikusika et al. (2019) [27]
	Dohne-Merino rams	40 g of FSF/kg	Enhances growth performance and contributes to the mitigation of heat stress	Mwanda et al. (2020) [28]
			Enhances feed intake, body condition score, and feeding behaviour by increasing the palatability and overall acceptability of the diet	Ikusika & Mpendulo (2023) [29]
Azadirachta indica and Moringa oleifera Leaf Extracts	Dohne-Merino wether lambs	50 mg/kg of feed	No statistically significant effects on carcass traits (p > 0.05), though meat % ↑ and fat % ↓ numerically	Webb et al. (2022) [30]
Curcuma longa	West African Dwarf breed of doe goats	TRP at 10 g of TRP/300 g of feed	Improved goats’ performance	Omotoso et al. (2022) [31]
Probiotics: Bacillus subtilis and Bacillus licheniformis (3.2 × 109 CFU/g) Essential oils: eugenol (17%), capsicum (7%), and cinnamaldehyde (11%).	Bonsmara weaners	probiotic (2.75 g/animal/day), or essential oils (3.21 g/animal/day	ADG and feed intake were statistically comparable to monensin, but FCR was significantly better with PRO, indicating functional equivalence with superior efficiency	Linde et al. (2023) [32]

The ↓ symbol means there was a decrease and the ↑ symbol means there was an increase.

. This study found no significant effect on cold carcass weight (CCW), meat percentage, fat percentage, bone percentage, or intramuscular fat (IMF%) compared to control or monensin groups (p > 0.05 for all). Meanwhile, carcass fat content (CFC t-scores) showed a numerical difference (Moringa 45.4 vs. Control 50.3, p = 0.05), which implies equivalence. However, it is noteworthy that within the same study, Moringa supplementation significantly improved the nutritional composition of the meat, particularly its fatty acid profile, by increasing beneficial monounsaturated fatty acids and improving the unsaturated:saturated fatty acid ratio.

Therefore, the Dohne Merino sheep consistently demonstrated the best response to FSF supplementation across multiple production parameters, including substantial improvements in ADG and FCR.

For FCR improvement, fossil shell flour, extensively studied in Dohne Merino wethers and rams, demonstrated the most substantial and consistent improvements. Ref. [27] reported FCR improvements from 0.14 (control) to 0.19 (at 4% FSF inclusion of DM), representing a 35.7% improvement. Similarly, ref. [29] found an FCR improvement from 0.16 (control) to 0.21 (at 40 g/kg and 60 g/kg FSF), marking a 31.3% improvement. These consistent and statistically significant FCR improvements across multiple studies and different Dohne Merino animal types position FSF as the additive showing the highest and most reliable FCR improvement among the reviewed studies. In contrast, the Bacillus probiotic and essential oil combination tested by [32] in Bonsmara weaners did not demonstrate a superior FCR compared to the control or monensin groups. The FCR values for the probiotic (6.24) and essential oil (6.91) groups were not significantly better than the control (6.25) or monensin (6.25), and indeed, the essential oil group showed a numerically inferior FCR. This indicates limited or no significant FCR improvement for these additives in this study. Similarly, ref. [31] found no significant improvement in FCR with Curcuma longa supplementation in goats, with values ranging from 10.50 to 10.86 across treatment groups. Ref. [30], Focusing on carcass traits, significant FCR improvements were not reported for Azadirachta indica and Moringa oleifera leaf extracts in lambs.

3.3. Assessment of Risk of Bias

The risk of bias within the six studies included in this review was systematically evaluated using the SYRCLE Risk of Bias tool (

Table 4. Risk of Bias Ratings for Included Studies.

Bias Domain	Ikusika et al. (2019) [27]	Mwanda et al. (2020) [28]	Ikusika & Mpendulo (2023) [29]	Webb et al. (2022) [30]	Omotoso et al. (2022) [31]	Linde et al. (2023) [32]
1. Sequence generation	Low	Low	Low	Low	Low	Low
2. Baseline characteristics	Low	Low	Low	Low	Low	Low
3. Allocation concealment	Low	Low	Low	Low	Low	Low
4. Random housing	Low	Low	Low	Low	Low	Low
5. Blinding of caregivers	Yellow	Yellow	Yellow	Yellow	Yellow	Yellow
6. Random outcome assessment	Low	Low	Low	Low	Low	Low
7. Blinding of outcome assessor	High	High	High	High	High	High
8. Incomplete outcome data	Low	Low	Low	Low	Low	Low
9. Selective reporting	Low	Low	Low	Low	Low	Low
10. Other bias	Low	Low	Low	Low	Low	Low

), specifically designed for animal studies [33]. Most studies exhibited a low risk of bias in essential domains such as sequence generation, baseline characteristics, random housing, incomplete outcome data, selective reporting, and other potential sources of bias. All studies either described appropriate randomisation procedures or presented well-matched baseline groups, and no notable difficulties were identified regarding data attrition or reporting. However, none of the studies provided precise details regarding the blinding of caregivers, resulting in an unclear risk of bias for this domain across all included studies. A notable methodological limitation was the absence of blinding. All six studies failed to report whether outcome assessors were blinded to group assignments, which introduces a high risk of performance and detection bias (Figure 3).

4. Discussion

This systematic review comprehensively assessed the efficacy and sustainability of natural feed additives within ruminant livestock in the Sub-Saharan Africa region. Considering the increasing demand for cost-effective and environmentally sustainable production practices, there has been increasing interest in identifying viable alternatives to synthetic feed additives [14]. Therefore, the current review elucidates the potential natural feed, including extracts of neem (Azadirachta indica) and moringa (Moringa oleifera) leaves, Curcuma longa, fossil shell flour, probiotics, and essential oils. Regarding the review, natural feed additives can significantly improve ruminant livestock production in SSA [27,28,29,30,31,32].

4.1. Efficiency of Natural Feed Additives

4.1.1. Fossil Shell Flour

The present systematic review encompasses three studies that examine the effects of fossil shell flour supplementation in the diets of Dohne Merino sheep. Collectively, these studies provide robust evidence that FSF supplementation can enhance both feed intake and growth performance in ruminants, with marked benefits specifically observed in Dohne Merino rams [27,28,29]. As the level of FSF inclusion in the diet increases, ranging from 20 g/kg to 60 g/kg, there is a consistent and significant improvement in average daily feed intake and ADG [29]. Notably, rams receiving 40 to 60 g/kg of FSF not only consumed greater quantities of feed but also exhibited superior growth performance compared to those maintained on control diets comprising hay and concentrate mixtures or lower FSF inclusion rates [29]. A noteworthy behavioural observation is the increased coefficient of preference for diets containing higher FSF levels (up to 60 g/kg), indicating that sheep not only consumed more but also demonstrated a clear preference for FSF-supplemented rations [29]. This finding underscores the palatability and acceptability of FSF as a feed additive among ruminants. Importantly, the observed improvements in animal performance are not solely attributable to increased feed intake but also reflect enhanced feed efficiency [27,28,29]. Specifically, ref. [27] demonstrated that inclusion of FSF improves the conversion of feed into body weight, signifying more efficient nutrient utilisation.

Studies confirmed that the inclusion of FSF up to 6% or 60 g/kg of dietary dry matter does not negatively affect feed consumption or animal health, supporting its safe application in ruminant diets [27,28,29]. This outcome is particularly relevant for livestock producers seeking cost-effective and safe feed additives with no adverse effects on intake or metabolic function. Fossil shell flour supplementation is associated with improvements in body condition score (BCS), a key indicator of animal well-being and productivity [29]. Higher BCS values were recorded in rams receiving the maximum FSF inclusion rate, highlighting the additive’s role in maintaining body reserves and energy status [29]. Furthermore, biochemical analyses revealed improvements in blood parameters, including elevated total plasma protein (TPP) and glucose (GLU) concentrations, as well as significantly increased red blood cell (RBC) and white blood cell (WBC) counts in FSF-supplemented rams [28]. These findings suggest enhanced metabolic activity, which contributes to an overall better physiological status and disease resistance. Concerning nitrogen metabolism, ref. [27] indicates that nitrogen intake and urinary nitrogen excretion remain relatively stable across different FSF inclusion levels. However, nitrogen balance tends to decrease as FSF inclusion increases [27]. While a reduction in nitrogen balance might typically imply lower nitrogen retention, within this context, it may reflect improved nitrogen utilisation efficiency and reduced nitrogen waste. Consequently, FSF supplementation could contribute to lower environmental nitrogen pollution, an outcome of growing importance in the pursuit of sustainable livestock production systems.

The consistent efficacy of FSF in enhancing performance parameters across Dohne Merino sheep is evident, with studies by [27,28,29] consistently demonstrating improvements in feed intake, ADG, and feed efficiency in both rams and wethers. A critical inquiry arises regarding whether FSF exhibits superior efficacy in rams compared to wethers, a distinction potentially rooted in their inherent metabolic differences. Rams, as intact males, possess a distinct hormonal profile characterised by higher testosterone levels. This anabolic hormone drives greater lean tissue accretion and typically results in higher basal metabolic rates compared to castrated wethers, which tend to partition more energy towards fat deposition. This fundamental physiological divergence suggests that rams inherently possess a greater genetic and hormonal predisposition for rapid lean growth and higher nutrient turnover, setting a different metabolic stage for the utilisation of dietary interventions.

Consequently, FSF’s proposed mechanisms of action, including improved gut health, enhanced nutrient absorption, and the provision of essential minerals, could theoretically translate into a more pronounced phenotypic response in rams. Their elevated anabolic state and higher metabolic demands might enable them to more effectively capitalise on the optimised nutrient availability fostered by FSF, leading to a greater magnitude of improvement in growth and feed conversion. While both [27,29] reported substantial FSF-induced improvements in ADG (43.3% in wethers and 53.5% in rams) and FCR (35.7% in wethers and 31.3% in rams), these studies were conducted independently on different animal types.

Feeding FSF significantly improves animals’ ADG and overall growth through a multi-pronged approach that enhances nutrient utilisation and optimises gastrointestinal health. Primarily, FSF’s porous structure and abrasive properties improve nutrient digestibility and absorption, allowing animals to extract more energy and protein from their feed, which directly boosts ADG, as consistently observed in studies on Dohne Merino sheep [27,28]. Beyond this, FSF supports enhanced gut health and reduces parasite load; its sharp, irregular particles can act as a natural anthelmintic, diminishing parasitic burden and preventing nutrient diversion, while also potentially binding mycotoxins [27]. This healthier gut environment leads to more efficient nutrient absorption and less metabolic stress, freeing up vital energy for growth. Although not typically considered a primary mineral supplement, FSF’s trace element content, particularly silicon, can also contribute to overall animal health and structural growth [29]. Ultimately, these combined effects improved digestibility, enhanced gut integrity, and potential mineral contributions, leading to better feed intake and efficiency, ensuring more consumed feed is effectively converted into body mass, directly increasing ADG.

The significance of FSF is particularly within SSA, where livestock production systems are commonly constrained by limited access to high-quality commercial feeds, elevated input costs, and heightened vulnerability to the effects of climate change. Conventional feed additives, such as antibiotics and synthetic growth promoters, are frequently either economically prohibitive or discouraged in response to growing concerns regarding antimicrobial resistance and adverse environmental impacts [9]. In contrast, FSF presents a cost-effective, locally available, and environmentally sustainable alternative. Its demonstrated capacity to enhance feed efficiency and physiological performance without necessitating substantial modifications to existing feeding practices renders it an especially attractive option for smallholder and resource-limited livestock producers. Furthermore, the mineral composition of FSF, which includes silica, calcium, and various trace elements, may contribute to improvements in animal health and structural development, thereby reducing reliance on synthetic mineral supplements.

4.1.2. Curcuma Longa (Turmeric Rhizome Powder)

Turmeric rhizome powder (TRP), derived from Curcuma longa, has emerged as a promising natural feed additive for ruminant production, particularly within goat husbandry. As reported by [31], TRP is characterised by a high dry matter (DM) content of 90.31%, which substantially exceeds that of conventional feed components such as concentrates (85.39%) and Panicum maximum grass (27.24%). This elevated DM content suggests that TRP can deliver a more concentrated source of nutrients per unit of feed, an advantage of relevance in feed-limited regions such as Sub-Saharan Africa. Moreover, TRP provides a slightly higher crude protein (CP) content (10.24%) compared to concentrates (10.05%) and a markedly greater level than grass (5.35%), underscoring its value as a supplemental protein source. The relatively low crude fibre content of TRP (8.04%) further enhances its digestibility, while its higher ether extract (4.58%) and nitrogen-free extract (73.52%) values contribute to increased energy availability for the animal [31]. Notably, TRP contains curcumin at a concentration of 0.76 mg/g, a bioactive compound recognised for its antioxidant, antimicrobial, and anti-inflammatory properties [31]. These attributes suggest that TRP may confer additional benefits for gut health and rumen efficiency beyond its nutritional value. Performance data from [31] further substantiate the advantages of TRP supplementation; goats receiving a daily inclusion of 10 g TRP per 300 g of feed demonstrated the highest crude protein intake (90.43 g/day), superior nitrogen retention (93.17%), enhanced daily weight gain (55 g/day), and an optimal feed conversion ratio (FCR) of 9.96, relative to control groups. These findings indicate more efficient nutrient utilisation and improved growth performance, both of which are critical for enhancing productivity in small ruminants. Moreover, the frequency of TRP supplementation was found to exert a significant influence on rumen microbial populations, and increased feeding frequency was associated with reductions in total bacterial count (and rumen pH, alongside increases in total fungi count, coliform count, and total volatile fatty acid production), reflecting enhanced rumen fermentation activity [31]. While Curcuma longa has garnered interest in its potential to enhance nutrient intake, growth performance, and rumen fermentation characteristics in goats, as explored by [31], the observation of an increased coliform count in supplemented groups warrants scrutiny. Coliform bacteria are commonly used as indicators of faecal contamination. They can include opportunistic pathogens such as Escherichia coli, some strains of which are pathogenic and can pose direct health risks to the animals or, in some cases, to humans through the food chain [34]. Therefore, the observed rise in coliform populations is indeed a safety concern, as it signals a potential shift towards gut dysbiosis or an increased bacterial load that could compromise intestinal integrity, lead to subclinical infections, or impact animal health and productivity overall [34]. This necessitates stringent monitoring of animals receiving turmeric supplementation, including regular assessment of faecal microbiology and animal health status, to mitigate these potential health risks.

Regarding the optimal dosing frequency, ref. [31] investigated the effects of once-a-week versus alternate-day supplementation frequencies compared to a control. Crucially, their findings indicated no significant difference in daily weight gain or feed conversion ratio across these varying feeding frequencies, suggesting that more frequent dosing did not translate into superior performance benefits. Given this lack of incremental performance advantage and the concurrent observation of increased coliform populations, the optimal dosing frequency must prioritise not only efficacy but also animal health and safety. Therefore, a less frequent dosing regimen, or indeed a re-evaluation of the overall supplementation strategy if coliform increases are a consistent side effect, would be preferable to minimise potential dysbiosis without compromising productivity.

The incorporation of TRP into ruminant diets offers substantial potential benefits for livestock production systems in SSA. As a locally available and naturally derived feed additive, TRP can significantly reduce dependence on expensive commercial supplements, making it a remarkably accessible and cost-effective choice for smallholder farmers [31]. Turmeric rhizome powder is comparatively high in protein and energy content and supports enhanced growth performance and improved feed conversion efficiency, attributes that are especially valuable in SSA, where feed quality is frequently suboptimal and access to quality protein sources is limited [31]. The demonstrated improvements in nitrogen retention and daily weight gain among goats supplemented with TRP directly contribute to increased meat and milk yields, thereby boosting farm productivity, household income, and food security for rural communities. The bioactive components within TRP, such as curcumin, which is a potent free radical scavenger, directly neutralise reactive oxygen species and reactive nitrogen species [35,36].

Furthermore, it enhances the activity of the body’s endogenous antioxidant enzymes, such as superoxide dismutase, catalase, and glutathione peroxidase [37], which are thought to foster beneficial rumen microbial activity while suppressing pathogenic bacteria [31]. These compounds neutralise free radicals and enhance the activity of endogenous antioxidant enzymes such as superoxide dismutase and glutathione peroxidase [38]. In ruminants, improved antioxidant status is associated with reduced oxidative stress, better immune response, and potentially improved meat oxidative stability [39]. This dual effect not only enhances digestive health and reduces the incidence of gastrointestinal disorders but also supports efforts to minimise the use of antibiotics in animal production, aligning closely with global priorities to curb antimicrobial resistance. Enhanced feed efficiency associated with TRP supplementation also means that less feed input is required to achieve the same level of output, which helps lower production costs and reduce the environmental impact of livestock farming. In regions affected by climate variability and environmental stressors, the functional properties of TRP may further promote animal resilience and adaptability.

4.1.3. Probiotic (EO) and Essential Oil (PRO)

The study by [32] provides valuable insights into the use of Bacillus-based probiotics and essential oils (as potential alternatives to the ionophore monensin in the diets of Bonsmara weaners), a critical consideration for sustainable ruminant production. Their findings revealed distinct effects on rumen microbial populations and fermentation patterns depending on the additive and feeding phase. During the starter phase, monensin supplementation significantly lowered the acetate-to-propionate ratio, a key indicator of enhanced rumen fermentation efficiency that favours energy utilisation for the host [32]. This beneficial shift was associated with a higher abundance of Succinivibrionaceae, a microbial family well-recognised for its role in propionate production [40]. In contrast, the EO group demonstrated a significantly higher abundance of Lachnospiraceae, a group of microorganisms heavily involved in fibre digestion and butyrate production, suggesting that EOs may promote alternative, potentially fibre-utilising, fermentation pathways within the rumen [32]. Moving into the finisher phase, the probiotic group notably exhibited greater bacterial diversity, a characteristic indicative of a more stable and resilient rumen microbial ecosystem, which is often associated with improved gut health and digestive robustness [32]. While no significant differences were observed in the alpha diversity of fungal populations, the probiotic group displayed the lowest abundance of Proteobacteria, a phylum that includes several opportunistic pathogens. This reduction in potentially harmful bacteria implies potential health benefits and improved gut integrity associated with probiotic supplementation [32]. Overall, despite these subtle, specific differences in microbial populations, the general composition of the rumen microbiome did not vary markedly between the monensin and alternative treatment groups. This overarching similarity suggests that both essential oils and probiotics may effectively replicate some of the beneficial effects of monensin on rumen function and animal performance. The strategic application of essential oils and probiotics, therefore, presents a promising strategy for enhancing growth performance, supporting gut health, and reducing reliance on synthetic antibiotics, which is crucial for advancing more resilient and sustainable ruminant production systems within the region.

4.1.4. Azadirachta indica and Moringa oleifera Leaf Extracts

The study conducted by [30] investigated the effects of plant extract-based dietary supplements, specifically neem and Moringa oleifera leaf extracts, on lamb performance and meat quality. While the supplementation of these extracts did not significantly influence overall carcass characteristics such as yield or gross composition, notable improvements in the nutritional composition of the meat were observed, particularly in lambs receiving Moringa oleifera leaf extract. Lambs supplemented with Moringa exhibited a significantly higher concentration of oleic acid (C18:1n9c), a monounsaturated fatty acid recognised for its cardiovascular health benefits, with content reaching 45.0% ± 0.57, compared to 40.5% ± 0.80 in the monensin group. Furthermore, the total monounsaturated fatty acid (MUFA) content was also elevated in moringa-supplemented lambs (47.3% ± 0.66) relative to those receiving monensin (42.6% ± 0.87). Crucially, the ratio of unsaturated to saturated fatty acids (UFA: SFA, a key indicator of healthier meat fat composition) was significantly more favourable in the moringa group (1.01 ± 0.03) than in the monensin group (0.85 ± 0.03). The improved fatty acid composition of meat in animals fed Moringa, particularly the desirable increase in unsaturated fatty acids (UFAs), is a result of Moringa’s unique phytochemical profile influencing rumen metabolism. Moringa leaves are rich in bioactive compounds such as polyphenols, saponins, and tannins [41,42]. These compounds are hypothesised to modulate or partially inhibit specific rumen microbes responsible for biohydrogenation. In this process, beneficial unsaturated fatty acids from the diet are converted into less healthy saturated fats. By mitigating this conversion, Moringa allows more UFAs, including oleic acid, to bypass the rumen and be deposited into muscle tissue, leading to an elevated total monounsaturated fatty acid content, as observed in moringa-supplemented lambs [30].

Furthermore, Moringa’s robust antioxidant properties protect susceptible unsaturated fatty acids from oxidation throughout digestion and in the meat itself, ensuring their preservation [42]. This combined action results in a significantly more favourable ratio of unsaturated to saturated fatty acids (UFA: SFA), yielding a healthier and more nutritionally valuable meat product [30]. These results highlight a critical distinction for ruminant production systems. At the same time, plant-based supplements may not enhance conventional growth performance or carcass yield. Still, they can substantially improve the health-related quality of meat by increasing the proportion of beneficial unsaturated fatty acids. The reviewed study by [30] found no statistically significant differences in key carcass characteristics, including cold carcass weight, dressing percentage, or fat and muscle composition between the control and herbal extract treatments. This highlights a critical distinction in ruminant production: enhancement of growth metrics does not necessarily translate to superior meat quality. For ruminant output in Sub-Saharan Africa (SSA), where consumer demand for healthier and more natural animal products is increasing, the strategic incorporation of locally available and sustainable feed additives such as Moringa can significantly enhance product value without necessarily compromising animal productivity. This approach supports market differentiation and value addition in both domestic and export meat markets, thereby contributing to improved farm income and positive public health outcomes [11].

4.2. Limitations of the Study

While this systematic review provides valuable insights into the efficiency and sustainability of natural feed additives in ruminant production feed in Sub-Saharan Africa from 2000 to 2024, it is subject to several limitations. Firstly, the scope of the systematic review databases used inherently constrains the findings. In this study, only four databases were used: Scopus, ScienceDirect, Web of Science, and EBSCOhost (Academic Search Ultimate). Though these databases are the largest yet, other databases are not considered but may have some information in the field of study. Also, only articles written in the English language were considered. Articles written in other languages, such as French and Portuguese, mainly from central and parts of western Africa, were not included. Lastly, studies from places other than sub-Saharan Africa and before the year 2000 were not included in this present study. However, despite these limitations, this study provides a foundational overview of the structure, growth, and thematic orientation of the use of feed additives in the ruminant production domain. Future review endeavours would benefit from integrating more regions, utilising more databases, and triangulating with qualitative methods for a more comprehensive understanding of the field’s evolution and global relevance.

5. Conclusions

This review highlights the considerable potential of natural feed additives such as plant extracts, essential oils, probiotics, and mineral-based supplements, including fossil shell flour, as sustainable alternatives to conventional growth promoters within ruminant production systems across Sub-Saharan Africa. The evidence demonstrates that these additives can deliver measurable benefits, including enhanced growth performance, improved feed efficiency, modulated immune responses, and superior meat quality, all while contributing to environmental sustainability through reduced nitrogen excretion and decreased reliance on antimicrobial agents. Nevertheless, variability in efficacy across different species, dosages, and feeding systems underlines the importance of further standardised, long-term, and region-specific research. Future investigations should also address the economic feasibility of these interventions, their practical adoption by farmers, and their performance under actual field conditions. Strengthening local research capacity and fostering innovation in natural feed technologies will be critical to advancing resilient and sustainable ruminant production systems, ensuring they can meet the region’s escalating demand for animal protein while safeguarding animal health and environmental integrity.