The Role of Agro-Industrial By-Products for Sustainable Livestock Systems

Introduction 

Livestock production plays a crucial role in meeting the global demand for animal protein. However, conventional feed resources, such as maize and soybean meal, face increasing pressure from competition with human food needs and limited land availability. This situation is exacerbated by rising feed costs and erratic supply, particularly affecting small-scale farmers. These challenges contribute to feed shortages, which significantly constrain ruminant productivity, especially during dry seasons. Therefore, exploring and utilizing alternative feed resources (AFRs) are paramount for developing sustainable and cost-effective animal production systems globally.

Agro-industrial by-products (AIBPs) and crop residues represent a vast and often underutilized pool of potential feedstuffs. Proper utilization of these materials can offer significant benefits, including reducing reliance on imported raw materials, lowering feed expenses, which are a major component of production costs, promoting a circular economy by converting waste into valuable feed, and mitigating environmental pollution associated with waste disposal.  Significant research has been conducted to assess the potential of various AIBPs and unconventional feedstuffs across different livestock species. Studies have investigated their impact on nutrient composition, in vitro digestibility and fermentation characteristics, and in vivo effects on animal performance, health, and product quality. 

At a Glance: Alternative Feed Options for different species

Cattle

• Distillers’ grains with solubles (DGS)
• Asparagopsis seaweed
• Palm kernel cake (PKC)
• Dried brewers' grains and molasses
• Rice bran

Sheep and Goats:

• Olive cake
• Citrus pulp
• Acacia nilotica foliage
• Cowpea haulms, Gmelina leaves, citrus peels
• Groundnut vs cowpea haulms

Poultry

• Cassava peels
• Wheat offal
• Rice bran with betaine supplementation

Pigs

• Grape pomace
• Citrus pulp
• Black soldier fly larvae meal
• Palm kernel cake (PKC)
• Maize offal and brewers’ dried grains (BDG)
• Olive cake

Rabbits

• Cottonseed meal (CSM) with lysine
• Crotalaria retusa leaves (ensiled)

Cattle

Agro-industrial by-products significantly influence methane emissions and meat quality in cattle. Salami et al. (2019) found that distillers' grains with solubles (DGS), when included at 40% of dry matter (DM), reduced methane emissions by ~15% while enhancing meat fatty acid profiles (e.g., increased conjugated linoleic acid). Similarly, Ahmed & Nishida (2024) demonstrated that Asparagopsis seaweed supplementation (0.50% DM) reduced methane by 95.6% in vitro, outperforming isolated bromoform (59.6% reduction), likely due to synergistic compounds in whole seaweed. However, high-fat by-products like DGS may increase nitrogen excretion, necessitating balanced diets (Salami et al., 2019). In contrast, rice bran, though low in methane yield (Ogunbosoye & Salau, 2020), offers limited energy, highlighting trade-offs between environmental and nutritional outcomes. 

In Bunaji calves, palm kernel cake (PKC) inclusion up to 30% improved weight gain and feed efficiency (Sani et al., 2019). Similarly, dried brewers' grains and molasses combinations reduced feed costs while maintaining productivity (Egbunike & Ikpi, 1990). These findings underscore the potential of by-products to enhance sustainability, though optimal inclusion levels and cost-effective processing require further study. Future research should prioritize in vivo trials to validate in vitro results and assess long-term impacts on herd health and productivity.

Sheep and Goats

In small ruminants, agro-industrial by-products improve feed efficiency and product quality. Luciano et al. (2013) reported that lambs fed 35% olive cake had extended meat oxidative stability due to elevated vitamin E levels. Similarly, Chiofalo et al. (2020) observed improved intramuscular fat and fatty acid profiles in young bulls fed olive cake (7–15% DM), though excessive inclusion (>30%) in pigs reduced carcass weight (Liotta et al., 2019). Citrus pulp, at 30% inclusion, maintained lamb growth without adverse effects, but higher doses (45%) impaired feed conversion (Caparra et al., 2007). Additionally, Acacia nilotica foliage reduced nematode egg counts in lambs via condensed tannins, though polyethylene glycol (PEG) supplementation negated this benefit by binding tannins (Akkari et al., 2008). These results emphasize the importance of moderate inclusion and tailored processing (e.g., ensiling) to maximize benefits. Future studies should explore interactions between by-products and regional feedstuffs to optimize diets for diverse farming systems. Studies on Red Sokoto goats highlight the potential of cowpea haulms, Gmelina leaves, and citrus peels. Onwusiribe et al. (2019) found that replacing 50% of cowpea shells with Gmelina leaves improved dry matter intake and weight gain, while Yashim et al. (2016) noted cowpea haulms outperformed groundnut haulms in nitrogen balance. Sweet orange peel meal (Yashim et al., 2016) did not compromise health markers at graded levels. 

Poultry

Cassava peels and wheat offal are commonly used in poultry diets. While long-term cassava peel use caused embryogenesis issues in goats (Egbunike & Ikpi, 1990), betaine could counteract cyanogenic compounds and improve feed efficiency (Dobrijević et al., 2023). Tewe & Egbunike (1988) noted agro-industrial by-products sustain poultry productivity during feed shortages. Further studies should evaluate betaine’s role in enhancing the metabolizable energy of fibrous by-products like rice bran.

Pigs

Agro-industrial by-products like grape pomace and citrus pulp enhance pork quality but require careful dosing. Tian et al. (2023) found that 10% grape pomace inclusion increased meat antioxidant capacity and juiciness, while Yu et al. (2019) noted that 4% black soldier fly larvae meal improved loin marbling and omega-3 content. However, higher inclusions (8%) reduced digestibility, underscoring the need for moderation. Citrus pulp at 50–100 g/kg DM shifted gut microbiota favorably and increased oleic acid in pork fat (Cerisuelo et al., 2010), but olive cake beyond 5% lowered carcass yields in pigs (Liotta et al., 2019). These findings suggest that by-products can replace conventional feeds without compromising quality if inclusion levels are calibrated. Future research should investigate the economic feasibility of large-scale by-product integration and their effects on reproductive performance. Palm kernel cake (PKC), maize offal, and brewers’ dried grains (BDG) are viable alternatives to conventional feeds. Adesehinwa (2007) demonstrated that 100% maize replacement with PKC maintained growth performance, while low-energy diets with agro-industrial by-products reduced fat deposition (Mauch et al., 2014). 

Rabbits

Agro-industrial by-products like cottonseed meal (CSM) and Crotalaria retusa leaves have shown promise in rabbit diets. Abdulrashid et al. (2019) found that lysine supplementation in CSM-based diets improved growth performance, though control diets (without CSM) yielded superior results, likely due to gossypol toxicity in CSM. Similarly, Yashim et al. (2017) reported that ensiled Crotalaria retusa leaves (5% inclusion) enhanced nutrient intake and weight gain compared to air-dried or oven-dried leaves, suggesting that processing methods mitigate anti-nutritional factors. 

Conclusion

Despite promising findings, the variability in the nutritional composition of AIBPs, influenced by processing methods and source, necessitates careful evaluation before inclusion in diets. The presence of anti-nutritional factors and secondary compounds like gossypol, cyanide, tannins, and saponins can limit the use or require specific processing or supplementation strategies to mitigate potential negative effects on animal health and nutrient utilization. The optimal inclusion levels of AIBPs vary widely depending on the specific by-product, animal species, age, and physiological state. High inclusion levels or long-term feeding of certain by-products require careful assessment. While in vitro studies provide valuable initial insights, there is a recognized need for more in vivo studies to validate these findings under practical feeding conditions and assess the full impact on animal performance, health, and long-term effects. Furthermore, there is a lack of data on the effects of many alternative feed resources on reproductive performance and product quality in small ruminants, which are crucial considerations for sustainable production and consumer acceptance. Finally, farmer characteristics and the support of public institutions could play a significant role in the actual adoption of AIBPs as innovative feed inputs.

Future Research Directions

Key gaps include long-term in vivo trials, economic analyses of by-product integration, and synergistic combinations of methane-reducing ingredients (e.g., tannins with lipids). Additionally, region-specific studies are needed to adapt findings to local agroecosystems.

References

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