Introduction
Feed shortage remains one of the most pressing challenges limiting the productivity of ruminant animals in Nigeria and other African countries, especially during the dry season. In Nigeria, ruminant animals are raised majorly on pasture grasses and legumes. As a result of seasonal variations in rainfall patterns, pastures available in the dry season are low in nutritional value, less digestible, and insufficient to meet the needs of the animals (Babayemi et al., 2009). The inability to meet the nutritional requirements of the animals will result in low production, poor growth, and poor performance.
There is a need for a sustainable approach to ensure a continuous feed supply for ruminants during the dry season to meet the growing population's demand. Using agro-industrial by-products (AIBPs) is an environmentally friendly approach that can be incorporated into animal nutrition. It has the advantage of reducing costs, promoting a circular economy, and climate-resilient agriculture. Additionally, Utilizing AIBPs in animal nutrition will improve livestock productivity and facilitate the achievement of sustainable development goals (SDG) 2 and 13.
Agro-industrial by-products are waste products of agricultural processing industries such as fruit and vegetable processing, oilseed extraction, brewery (Maria, 2018), and root and tuber processing. They can be fed solely to animals or mixed with other feed ingredients to meet the animal's requirements (Lamidi and Ologbose, 2014).
This article aims to review cassava peel, brewer’s spent grain, and cotton seed cake as AIBPs, in terms of their nutritional value, limitations, and sustainability impact.
Nutritional Value and Limitations
Cassava Peel for Animal Feed
Cassava is a perennial crop that has the potential to perform well under poor conditions, as a result, it can be available all year round (Kolawole et al., 2010). Nigeria, one of the world's largest producers of cassava, produces about 15 million tons of wet peels per year (Natalie Kinsley, 2021). Cassava peel is rich in carbohydrates but deficient in protein and sulfur-containing amino acids (Fasae and Yusuf, 2022). Supplementing the Cassava peel diet with rich protein sources or fermenting before inclusion in the diet has been reported to enhance protein content (Natalie and Mingan, 2016). The major limitations of fresh cassava peels are their phytate content and high cyanide content, which are poisonous to animals and cause fast spoilage. Studies have shown that effective processing such as sun-drying, ensiling, and inclusion of enzymes helps in reducing the toxicity in cassava peel, enhances digestion and preserves nutritional quality. (Salami et al., 2003; Eniolorunda and Rowaiye, 2008; Ibhaze et al., 2014).
Brewer's Spent Grain
This is produced in large quantities as a waste product of the brewing industry (Gadzama and Garcia, 2020). It accounts for approximately 85% of the total production (Sallhu and Muntari, 2011). Studies have reported that brewer's spent grain (BSG) contains 19-30% protein, 30-50% fiber, and components such as phenolic compounds, arabinoxylans, and protein in hydrolysates form, which have nutritional and health benefits (Mussatto, 2014, Steiner et al., 2015; Makombe and Gadzama, 2024). It is also rich in sugar and minerals. The nutritional composition varies due to factors such as the type of grain used, the brewery where it is produced, the harvesting time of the grain, the condition under which it was cultivated, malting conditions. (Robertson et al., 2010; Mussatto, 2014; Makombe and Gadzama, 2024). The major limitations to using BSG are the presence of anti-nutritional factors such as high lignin content and its high perishability due to its susceptibility to contamination, especially when wet. To preserve the nutritional content of BSG, it must be stored under appropriate post-production conditions such as soaking, ensiling, and drying. There are also suggestions that drying it to a moisture content of approximately 10% can improve storage (Wood et al.,1994; Bartolomé et al., 2002; Gadzama and Garcia, 2020). Wet BSG is deficient in calcium and phosphorus, and there, it should be supplemented with a well-balanced mineral supplement for optimum-performance ruminants (Megan et al., 2019).
Cottonseed Cake
It is produced during oil extraction from cottonseeds. It is an excellent source of protein, fiber, vitamin E, and phosphorus (Gadzama and Díaz, 2020), which can be incorporated into ruminant feed. The factors limiting the use of cottonseed cake (CSC) in ruminant nutrition are its deficiency in amino acids such as lysine, methionine, leucine, and isoleucine and the presence of anti-nutritional factors such as gossypol (Gadzama, 2024). Fortunately, ruminant animals can convert gossypol into bound gossypol in the rumen, preventing it from being absorbed into the blood (Gadzama and Díaz, 2020; Gadzama, 2024). Decorticating, dehulling, and treatment with phytate enzymes can help improve the nutritional value of CSC. Several researchers have documented that the supplementation of animal diets with CSC improved the performance of ruminant animals (Akinlade and Kibon, 2000; Assis et al., 2018; Webb et al., 2019; Gadzama and Díaz, 2020).
Sustainability Impact
Waste products from agricultural and food processing industries contribute tremendously to environmental pollution. For instance, in Nigeria, tons of cassava waste is produced during cassava processing. Most of this waste is left to rot or burnt to create room for more heaps of waste, emitting carbon dioxide and offensive odor into the environment (Adebayo, 2008; Aro et al., 2010). This is hazardous to the health of humans and animals. Utilizing these products will help reduce food waste's environmental footprint and promote the achievement of SDG 12, Responsible Consumption and Production. It offers an economic advantage to ameliorate environmental pollution efficiently.
Additionally, using AIBPs in animal nutrition helps minimize the competition for land and feed ingredients, as most of these byproducts are not consumed by man. The cost of feed materials, both locally produced and imported, is high, so incorporating AIBPs is less costly and readily available. This will minimize production costs and enhance the productivity and profitability of the ruminant industry.
Conclusion
The use of agro-industrial by-products in ruminant nutrition offers several advantages, including reducing nutritional costs, minimizing food wastage, promoting a circular economy, and enhancing environmental sustainability. These by-products are rich in essential nutrients such as proteins, carbohydrates, vitamins, and minerals. Although some AIBPs contain anti-nutritional factors, studies have shown that they can be utilized as animal feed when properly processed. Due to the variation in the composition of AIBPs, it is important to determine their proximate composition before incorporating them into animal feed.
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