Selected documents were examined in detail and underwent a complete review. The final publications were imported into Zotero, which identified the nature or type of document that was being recorded. Questions were then developed following the method by (27) method to show how alternative feeds are used in West Africa based on literature published between 2013 and 2023. We took into account general characteristics of the articles such as title, year of publication, country of study, affiliation of the main author, and links to alternative feeds.

The documents found include articles (79.2%), which are the most prevalent documents, followed by abstracts (16.7%), book chapters (2.1%), and conference papers (2.1%) (Figure 2).

Regarding the year of publication, the number of documents used for this review was approximately 4% from 2013 to 2020. However, the highest number was obtained in 2021 (27.3%) and dropped 2 years later. This increasing trend can be explained by the abundance of publications on this subject, which is becoming more and more important and a topical issue for decision-makers in order to improve the livestock sector (Figure 3).

Benin is in first place, with 39% of publications, followed by Burkina Faso and Nigeria (22%) (Figure 4). Ivory Coast, Mali and Niger are included in the same proportion (6%).

We identified six groups of feeds, distributed as follows: Agro-industrial by-products (48.89%), fodder trees (17.78%), crop residues (13.33%), and insects (8.89%). In addition, we found fodder legumes (6.67%), followed by seaweeds (4.44%) (Figure 5).

The use of alternative feeds varies by farming system. Our study showed that intensive systems used 48% of the identified feeds, compared with 30% in semi-intensive systems and 21% in extensive systems (Figure 6). The percentage obtained in the intensive systems can be explained by the strong integration of livestock and crops production systems. The low level observed in extensive systems can be explained by a lack of interest in animal feed, followed by a lack of financial resources for the supply of agro-industrial by-products. Difficult access to feed is also due to farmers’ mobility, which takes them far from feed sales outlets. In semi-intensive systems, livestock farming is sometimes seen as a secondary activity, so small herds are common. These farmers are generally located in urban areas, which justifies their limited use of feed.

Studies carried out between 2013 and December 2023 (Figure 7) show that several factors limited the availability of alternative feeds. These include climate change (41.8%), which affects not only agricultural land but also crop yields. The latter contributes to animal feed (33.3%). Variations in rainfall, extreme temperatures and the proliferation of harmful insects and pests are all threats to crop yields. In addition, land use (16.8%) due to increasing urbanization limits the production of livestock feed. Agricultural policies (8.3%), with their lack of interest in crop diversification, influence the availability and price of raw materials.

Climate change is expected to have several impacts on feed crops, thereby negatively affecting the availability of alternative feeds while altering their nutritional value and yield at the same time. According to Getu (28), one of the most important effects of climate change on livestock production is the change in feed resources because indirect effects on feed resources can have a significant impact on livestock production, the buffering capacity of ecosystems and their sustainability, the prices of stover and grain, trade-in feeds and changes in feeding options. Drought-induced by climate change and other anthropogenic activities can have adverse effects on horticultural crop production (29). It tends to induce the sprouting of tubers in potatoes (30). The consequences are a reduction in yield, water content and quality of vegetables, such as spinach (30). Drought increases the salinity in the soil, thus affecting osmotic potential and therefore water loss from plant cells, leading to reduced productivity (31). In addition to their basic nutritional value, fruits and vegetables are also rich in biologically active components, such as ascorbic acid, sugars, and phenolics, which provide health benefits (32). The concentration of many biologically active components can increase with increasing CO₂ levels, but there is also a decrease in protein and mineral content (33). Frequent exposure of fruit to high temperatures (35–40°C) can result in sunburn and loss of texture (34). Since temperature also has an effect on photosynthesis, the impact can be seen in different physio-chemical alterations in fruit and vegetable products, such as sugars, organic acids, firmness, and antioxidant activity (30, 34). In addition, some fruits stored at 0°C (below the recommended temperature), showed a lower incidence of chilling injury (e.g., color and texture of the fruit) than the same fruit harvested from the shaded parts of the tree (34). Post-harvest temperature management of fruits and vegetables is the most important factor in preserving vitamin C. Its losses are accelerated at higher temperatures and with longer storage times (32). Furthermore, in warmer climates, fruits and vegetables are harvested at higher pulp temperatures, which require more energy and refrigerants for proper cooling and may increase product prices (34). Many studies have shown that climate change has a negative impact on seaweeds. According to Khan et al. (35) an increase in greenhouse gas emissions has led to an increase in global average air and ocean temperatures. Increased sea surface temperatures may cause changes in the distribution of seaweed species, particularly those close to their thermal tolerance limits. Moreover, Sunny (36) found that the survival, growth, and reproduction of seaweeds vary with numerous environmental variables, including temperature, nutrient supply via upwelling and runoff, pH, and carbon dioxide concentration itself. As sea levels rise, the distribution and abundance of seagrass and seaweed habitats in any given location decrease. An increase or decrease in salinity impacts seagrass and seaweed. The potential effects of increasing CO₂ and the impacts of greater UV-B radiation will alter the photosynthesis and productivity of seagrass and seaweed, and the author concluded that there is a critical need for research on the direct effects of the various aspects of global climate change on seaweed and seagrass (36).

Alternative feeds are important sources of energy and protein that can be used in ruminant diets because they offer great advantages, such as sustainability, local availability, and resilience to climate change. They include crop residues and agro-industrial by-products, fodder legumes, fodder trees, insects, and algae. Their nutritional value includes dry matter (DM), organic matter (OM), nitrogen, crude cellulose, and fat content. The main methods for determining nutrients are spectrometers, official methods approved by the Association of Official Analytical Chemists, followed by linear regression to determine nutritional values. The nutrient values of alternative feeds are shown in the Table 1.

Several studies have shown the efficient use of alternative feeds through improved intake and digestibility (Table 2). According to (77), the highest daily feed intake (285.36 g/day), nitrogen intake (21.75 g/day), and nitrogen balance (9.37 g/day and 5.36 BW^0.75) were obtained using dried plantain and mango peels and concentrates in a ratio of 50:18:32 in the diet of West African dwarf goats. It is concluded that this ratio has the potential to enhance the nutrient utilization and growth performance of West African dwarf goats. Moreover, Abebe and Tamir (70) found that supplementation with forage legumes led to an increase in total dry matter, crude protein, and NDF intake and suggested that supplementation with Lablab purpureus resulted in improved nutrient intake in Wollo Tumele lambs. The authors also found that supplementation of 243 g of pigeon pea or 260 g of cowpea with 200 g of wheat bran per day and per animal could be recommended for intact Wollo Tumele lambs fed grass hay in order to improve feed and/or nutrient intake. Furthermore, Omotoso et al. (78) showed that Cajanus cajan had better nutritional values with 15.53% crude protein and 30.55% crude fiber and added that the inclusion of Cajanus cajan as a supplement to cassava peels in the goat diet significantly reduced dry matter intake. Crude protein intake increased with increased hay supplementation. Crude protein, crude fiber, NDF, ADF, and ADL intakes were highest in goats fed the diet (25% cassava +75% Cajanus cajan hay). Nutrient digestibility and retained nitrogen were highest in the 75% Cajanus cajan inclusion treatment. The study found that combining cassava peels with Cajanus cajan hay in a 1:3 ratio resulted in an improvement in nitrogen content, digestibility, and optimal levels. According to Kiatti et al. (49), fruit by-products can be used as a base for ruminant feed based on their nutritional content of sugar and fiber. Pineapple by-products, specifically the core and pomace, were found to have low structural carbohydrate content, high in vitro degradability, and high volatile fatty acid production. This study suggests that pineapple by-products can be used in ruminant nutrition; the crown, bud end, and peel can be use as fiber sources, while the core and pomace can be used as energy sources.

Alternative feeds show interesting results in ruminant production, especially for meat production (Table 3). According to Okoruwa et al. (77), dried plantain with mango peels and concentrates in a ratio of 50:18:32 has potential for growth performance in West African dwarf goats, recording a daily weight gain of 33.67 g and 13.98 BW^0.75. Based on these results, it is therefore concluded that the combination of dried plantain and mango peels in different proportions has good nutritional potential and could be the main component of goat rations. Mahmoud (79) found that Moringa oleifera stems are suitable for sheep feed because they can be used without any negative effect on Rahmani lambs. Furthermore, Idrissou et al. (11) studied the fattening performance of Djallonké sheep supplemented with Gliricidia sepium and Leucaena leucocephala fodder in central Benin. The evolution of the average daily gain per 15-day period was not significantly different between sheep from the first to the third-fortnight experiment. However, in the fourth fortnight, Djallonké sheep supplemented with Leucaena leucocephala and Gliricidia sepium, respectively, had a significantly higher average daily gain. Abebe and Tamir (70) found that supplementing Wollo Tumele lambs with 243, 260 or 225 g dry matter per animal per day of pigeon pea (Cajanus cajan), cowpea (Vigna unguiculata) and lablab (Lablab purpureus) in addition to ad libitum feeding of natural pasture grass hay and 200 g dry matter per animal per day of wheat bran resulted in average daily gains of 34.97, 20.33 and 49.36 respectively. These authors concluded that these forage legumes can be used to improve feed and/or nutrient intake and carcass yield characteristics. Studies on the effects of cassava and banana peels (12) showed that incorporating dried banana peels in the feed at 20% accelerated sheep growth and their average daily weight gain. Moreover, Kiéma et al. (13) showed that the use of Faidherbia albida pods improved the average daily gain from the eighth week and, therefore, the growth performance of young bulls. Similarly, studies by (60) on the effects of Cassia tora hay on the zootechnical performance of fattening Djallonké sheep fed rations R1 (75% cottonseed cake and 25% Cassia tora hay) and R2 (50% cottonseed cake and 50% Cassia tora hay) showed that the average daily gain induced by rations R1 and R2 was 80.7 and 71.1 g/animal/day, respectively. Their findings show that using Cassia tora leaves as a protein source replacement can improve feed intake, feed efficiency and feed conversion. A study on the combination of Moringa oleifera Lam. residues, sorghum stalks and wheat bran (80) showed that dried Moringa oleifera residues have the same crude protein content as groundnut hulls or cowpea leaves and total live weight gain varied from 1.88 to 2.35 kg and average daily weight gain from 20.83 to 26.11 g. They concluded that, in the future, livestock farmers will be able to collect, dry and store Moringa residues and use them as fodder in the same way as groundnut hulls or cowpea leaves.

Results of alternative feeds on milk production show that Spondias mombin extract improves milk production in ewes (14) with an average of 100.63 g/day (Table 4). According to Pamo et al. (15) who carried out studies on the chemical composition and effect of supplementation with Calliandra calothyrsus and Leucaena leucocephala on milk production in goats, fresh leaves of Calliandra calothyrsus and Leucaena leucocephala doubled production (361 g/d) in dairy goats. Studies by Sanogo et al. (16) on the effect of cereal straw, cowpea fodder, and cotton cake on improving milk production showed that the average cumulative milk production was 140 liters for cows in stalls. Further work like the study by Gbenou et al. (17) on the effect of sorghum meal supplementation on the milk production of cows (Gir × Borgou) showed the production of 3.3 kg milk/day with the supplementation of 2 kg of sorghum meal. Finally, Akouedegni et al. (81) showed that the average daily increase in milk production was 9.92, 14.25, and 18.88% in the single-dose, double-dose, and Galactin groups, respectively, compared to the control group in ewes treated with Spondias mombin leaf powder. Similarly, the findings of Seidou et al. (82) showed that forage legumes improve milk production in local cows, even in the dry season in the drylands of Benin.

The first factor limiting the widespread use of alternative feeds in animal nutrition is their high water content, which can often exceed 60–80% making them difficult to handle and store and leading to spoilage (21). Similarly, the seasonal availability of fruits and vegetables and their by-products also has an impact on feed production. In addition, anti-nutritional factors limit their incorporation into the diet. For example, red sorghum is rich in tannin and groundnut, and cotton and palm kernel cake contain aflatoxin, gossypol, and cellulose, respectively. Other factors such as rising food prices and stockouts are major obstacles to their use. Land use, climate change, followed by declining crop yields, and a lack of agricultural policies also affect the availability of alternative feeds. The effects of climate change (83) lead to the reduction of feed and water resources. This is also confirmed by Far (84), who showed that all the effects of climate change lead to local resource reduction due to higher temperatures, CO₂ affecting grazing land (85). In addition, Abdou et al. (86) showed that climate change causing higher temperatures and long periods of drought thus affecting alternative feeds production. These factors have negative impacts on ruminant farming because alternative feeds became scarce.

To mitigate the effects of climate change and improve agricultural production, the use of alternative feeds is proving to be a better option. Ahmed et al. (18) showed that dietary supplementation of animal fodder with Asparagopsis taxiformis at 1 and 2.5% reduced methane production by 21 and 80% respectively, while the inclusion of Euglena gracilis in the diet at 10 and 25% reduced methane production by 4 and 11%, respectively, with no negative effect on fermentation parameters. Similarly, Gryllus bimaculatus and Bombyx mori reduced methane production by 18 and 16%, respectively, (87). In addition, phytochemicals in the feed, such as tannins, saponins, and essential oils, could potentially modify the microbial flora and thereby reduce methanogens in the rumen (88). Moreover, tannins and other phytochemicals containing phenolic groups may be better at binding proteins and slowing down their degradation by rumen microbes (89). Tannins and rumen bacteria interactions or their suppression of fiber digestion may be directly or indirectly beneficial to reducing CH₄ production (90). According to Moate et al. (91), the addition of polyphenolic compounds to citrus by-products reduced CH₄ emissions by inhibiting the growth and activity of methanogens such as Methanomicrobium and Methanobrevibacter. The authors also showed that alfalfa hay reduced CH₄ emissions by 22.6%, with positive stimulation of rumen bacteria and archaea populations. Finally, studies on the chemical and nutritional characteristics of Cannabis sativa L. co-products (92), showed that all hemp co-products presented interesting nutritional characteristics, such as a crude protein content always higher than 20% on a dry matter basis, and a high neutral detergent fiber concentration partially lignified. Preliminary results underline that the use of hemp processing residues could be a valid nutrient resource in ruminant diets. The low methane values suggest that these residues could be used in ruminant diets to limit gas emissions, and therefore environmental impact.

To ensure the long-term use of alternative feeds, it is important to adopt low-cost preservation methods, such as dehydration and ensiling. These methods can help preserve feeds and improve their use for everytime. Glocusinolates can be removed from soybeans by cooking or toasting. Groundnut cake is detoxified using an aqueous ammonia solution, and gossypol is eliminated from cotton cake using iron sulfate (93). In addition, the following incorporation limits must be respected: red sorghum (30%), groundnut cake (25%), cottonseed cake (10%), and palm kernel cake (20%) for more efficient use (43). Furthermore, widespread dissemination of good pre- and post-harvest practices in the mango and cashew nut sectors, for example, must be known and mastered by users to minimize post-harvest losses. It can also ensure the quality of foodstuffs when fruits are harvested at the right stage of ripeness and then processed using an appropriate production process. To improve fruit and vegetable by-products, there is a need to build the capacity of actors in fruit processing, followed by material and financial support.

Further research is needed to evaluate the palatability and determine the optimal levels of inclusion of these feeds and by-products, which will be obtained from different plants grown under different conditions and extracted and processed by different methods. Biotechnology will be used to develop fruit varieties that are suitable for animal feed. Similarly, analytical methods must be developed to complete the measurement and categorization of micronutrients and phytochemicals in alternative feeds. In addition, the bioactivity, bioavailability, toxicity, and interactions of phytochemicals in alternative feeds with other feed components should be the subject of future research through in vitro and in vivo experiments.

This study excluded publications prior to 2013, given the evolution of scientific progress and the reliability of results using modern tools. Nevertheless, non-scientific or non-English scientific sources in other fields may contain information not considered in this review. If necessary, other reviews could focus on these sources. This confirms the need to focus attention on alternative feeds and study chemical compounds that limit their use in ruminant feeding. It will also be useful to develop feeding schedules that take into account West African realities to help improve feeding systems.