Livestock feed resources used as alternatives during feed shortages and their impact on the environment and ruminant performance in West Africa: a systematic review

Ruminant feed is a major problem for the livestock sector in West African developing countries causing animal nutritional diseases, reducing ruminant production, and creating a massive ecological crisis through greenhouse gas emissions. Alternative feeds, which include agro-industrial by-products, fodder trees, crop residues, insects, fodder legumes, algae, and pulses, constitute enormous feed resources for livestock in Africa. This study was conducted in accordance with the methodological recommendations of PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). We conducted a literature search using Google Scholar, Web of Science, and Scopus to identify documents related to alternative ruminant feeds using the following keywords: alternative feeds, ruminant products, environmental impacts, and West Africa. Those that met the inclusion criteria were included, resulting in 44 articles published between 2013 and 2023. These studies included 45 alternative feeds divided into six groups, including agro-industrial by-products (48.89%), followed by fodder trees (17.78%), crop residues (13.33%), insects (8.89%), fodder legumes (6.67%) and seaweeds (4.44%). Our results revealed that alternative feed resources and their effects on ruminant’s performances and environment are poorly known in West Africa, which limits their inclusion in rations and sometimes leads to their misuse. Future research should focus on these aspects in order to make efficient use of these resources to improve ruminant milk and meat production.


Introduction
In the face of population growth and land use through urbanization, which absorbs arable land and therefore the availability of animal feed resources, livestock production in Africa is no longer able to meet the population's demand for meat and dairy products.It is facing a huge feeding problem (1), which is a major cause of low milk and meat production in West Africa (2).This situation can be explained by the nutritional characteristics of grown forage (3) and a lack of knowledge on rationing techniques, resulting in lower animal productivity and considerable 10.3389/fvets.2024.1352235Frontiers in Veterinary Science 02 frontiersin.orggreenhouse gas emissions (4), contributing to global warming (5).It is well known that emissions cause an increase in temperature, and a decrease in rainfall (6) and have a significant impact on pastoral resources.This situation reduces the conditions necessary for ruminant production and makes West Africa the most affected by the effects of climate change in the world (7).The livestock sector contributes to global N flows through the application of synthetic N fertilizers and manure to both croplands and grasslands, the management and accumulation of manure, and the transport of N-rich products such as feed, food, and manure (8).In some cases, excess nitrogen is a source of air pollution (9).
To ensure food security with more livestock production, it is necessary to use alternatives in feeding practices.Thus, alternative feeds appear to be a promising option to improve the feed supply chain for ruminants and strengthen their availability in dry and rainy seasons.Alternative feeds also help to improve milk and meat production at a lower cost.Rice straw and other crop residues such as cereal stalks are rich in cellulose and provide nutrients for the growth of rumen microbes (10).Crop residues and agro-industrial by-products used as alternative feeds also deserve to be preserved for the future of ruminant farming.Furthermore, Idrissou et al. (11) found that Djallonké sheep supplemented with Leucaena leucocephala and Gliricidia sepium, respectively, had significantly higher average daily gains in Benin.Studies on the effects of cassava and banana peels (12) showed that incorporating dried banana peels at 20% in the feed accelerated sheep growth and average daily weight gain.Moreover Kiéma et al. (13) showed that the use of Faidherbia albida pods increase average daily weight gain of young bulls therefore seems to be an alternative way of improving livestock production (14).
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 the production (361 g/d) in dairy goats.A study by Sanogo et al. (16) on the effect of cereal straw, cowpea fodder, and cotton cake on improving milk production found that the average cumulative milk production was 140 liters for cows in stalls.Furthermore, the results of Gbenou et al. (17) revealed that the production of cows (Gir × Borgou) with the supplementation of 2 kg of sorghum meal resulted in a production of 3.3 kg of milk/day.According to Ahmed et al. (18) the combination of micro-and macroalgae as ruminant feeds can replace the expensive conventional sources in animal diets and help to reduce feeding costs and livestock impacts on environmental.Biologically active compounds, such as flavonoids found in by-products of the winery industry and citrus fruits, are gaining attention for their ability to modulate the immune system of ruminants (19), due to their positive effects on milk quantity and quality (20).According to Jalal et al. ( 21), fruit and vegetable by-products can be used as an alternative feed source for sustainable ruminant nutrition and production.The use of alternative feeds in ruminant nutrition would provide benefits and help alleviate the environmental problems associated with waste disposal (22).Including these by-products in ruminant diets could reduce the environmental impact of their disposal (23) and promote the growth of a circular economy by recycling the biomass derived from crop production (24).From a socio-economic point of view, it is possible to reduce ration costs, improve the income of livestock farmers, and develop the market for livestock feeds.Although these feeds are well known in West Africa, it has been observed that huge quantities are wasted.It is therefore necessary to focus on the availability, nutritional value, technical and economic limitations of these feeds, which vary from one agro-ecological zone to another, and consequently from one country to another.This review summarizes the results of various studies carried out on the nutritional value, ruminant products and environmental impact of using alternative feeds.The aim of this review was to enhance the value of locally available alternative feeds for ruminant feeding in all seasons through their efficient use in the formulation of balanced, climatesensitive rations to improve household incomes and protect the environment.

Methods
Reporting Systematic Reviews and Meta-Analyses of Studies were used for the current study.Recent studies conducted principally in West Africa (Benin, Burkina Faso, Nigeria, Niger, Mali, and Côte d'Ivoire) from 2013 to 2023 were accessed through Google Scholar, Web of science, and Scopus.The downloaded documents were retrieved using a combination of the following keywords: alternative feeds, ruminant products, and environmental impacts.The keywords were used first in French and then in English in order to obtain as many publications as possible.The references found were imported into Zotero software version 5.0.94.Documents were selected based on the recommendations of (25,26) by using a two-step process based on predefined criteria (Figure 1).The selection was based on titles, abstracts, and keywords.In total, 2,463 articles were obtained after excluding duplicates.In the second step, we based the selection on publication date, language (English or French), and research subject (alternative feeds for ruminants) in West Africa.As soon as the study topic appeared in any of the documents or was addressed in any other way, the article was downloaded and thoroughly checked.The selection criteria set out above were applied to the initial articles, resulting in the selection of 44 scientific publications (Figure 1).Publications for this synthesis were not analyzed as the only ones on the subject but were intended to provide a representative overview of alternative ruminant feeds in West Africa.The 44 articles finally selected were all in English.

Data management, review, and statistical analysis
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.
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).

Geographical distribution of articles
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%).Percentage occurrence of document types. 10.3389/fvets.2024.1352235 Frontiers in Veterinary Science 04 frontiersin.org

Alternative feeds in farming systems
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.

Factors limiting the availability of alternative feeds
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.Droughtinduced 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 CO 2 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 physiochemical 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 CO 2 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).

Nutritional value of alternative feeds
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.

Effect of using alternative feeds on dry matter intake and digestibility
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.

Effects of alternative feeds on average daily gain
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  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 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.

Effects of alternative feeds milk production and composition in ruminants
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.

Factors limiting the use of alternative feeds
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, CO 2 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.

Protecting the environment through the use of alternative feeds
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 CH 4 production (90).According to Moate et al. (91), the addition of polyphenolic compounds to citrus by-products reduced CH 4 emissions by inhibiting the growth and activity of methanogens such as Methanomicrobium and Methanobrevibacter.The authors also showed that alfalfa hay reduced CH 4 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 methane values suggest that these residues could be used in ruminant diets to limit gas emissions, and therefore environmental impact.

Technical options for improving the use of alternative feeds
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.

Prospects for research on alternative feeds
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.

Limitations of the review
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.

Conclusion
This review identified 45 alternative feeds that could benefit the livestock sector but poor management practices lead to livestock underfeeding during the dry season.We need to look at these resources to improve their use.Alternative feeds will be profitable for livestock by improving the processing systems from which they are derived.Based on the diversity of agroecological zones in West Africa and the uneven distribution of livestock, this offers opportunities for the emergence of feed production and marketing.This will provide support for mechanisms to establish and then strengthen feed assessments for livestock in West Africa.It will help to promote and improve livestock resilience to climate change and support policies for sustainable production.

FIGURE 1
FIGURE 1 Document selection diagram.

3
FIGURE 3Percentage of documents used from 2013 to 2023.

FIGURE 4
FIGURE 4Geographical distribution of articles.

FIGURE 6
FIGURE 6Trend toward alternative feeds in farming systems.

FIGURE 7 Factors
FIGURE 7Factors limiting the availability of alternative feeds.

TABLE 1
Chemical composition of alternative feeds.

TABLE 2
Effect of alternative feeds on dry matter intake and digestibility.

TABLE 3
Effects of alternative feeds on average daily gain.

TABLE 4
Effect of alternative feeds on milk production and composition in ruminants.