PROXIMATE ANALYSIS OF FIVE COWPEA [(Vigna unguiculata (L.) Walp.)] LINES AS FEED RESOURCES FOR RUMINANT PRODUCTION IN BURKINA FASO

The main food resource for ruminant production in Burkina Faso is natural grazing, which cannot sustain ruminant production all year round. Therefore, it is necessary to incorporate cultivated forages including crop residues such as fodder whose nutritional values must be verified before they are used in ruminant feed. To this end, samples of the fodder of five cowpea lines [(Vigna unguiculata (L.) Walp.)] created at the Saria station were analysed to determine their nutritional values using existing standard techniques. Obtained results revealed dry matter (DM) contents ranging from 91.12 to 91.50%, organic matter (OM) from 83.05 to 90.20%, crude protein (CP) from 13.98% to 17.47 and crude fiber (CB) from 26.45% to 31.85%. Lines BC3F10P34-3 and KVx745-11P contained the highest total nitrogen content and low average crude fiber values. Therefore, these two cowpea lines could be exploited in an appropriate feeding strategy for rural ruminant production.


Introduction
Burkina Faso has enormous potential for livestock production. According to Oudet (2005), agriculture and livestock occupy more than 85% of the population and contribute about 40% to the Gross Domestic Product (GDP) and 86.6% of the country's exports. Indeed, the livestock sector Http://www.granthaalayah.com ©International Journal of Research -GRANTHAALAYAH [60] is characterized by the existence of a large and diversified livestock population (MRA, 2012), particularly ruminants which contribute to food security and poverty alleviation (MRA, 2010; Zerbo and Siri, 2012). However, ruminant farming faces multiple constraints, including animal feeding, a major difficulty for livestock farmers due to the lack of natural pastures in all seasons and the reduction of grazing areas. However, most of their breeding is extensive and depends on natural pastures for livestock feed. This is the reason for the considerable decline in animal productivity particularly that of ruminants in the dry season, mainly due to the quantitative and qualitative shortage of spatio-temporal fodder during this time of year (Kaboré-Zoungrana, 1995). One of the technical options to curb overgrazing and improve ruminant productivity during lean periods is to increase the use of agricultural by-products in animal feed, particularly legumes. Among these legumes, cowpea [(Vigna unguiculata (L.) Walp.)] is important because of his protein content, which varies from 20.5 to 31.7% (Onwuliri and Obu, 2002), and its vitamins and minerals values compared to herbaceous pastures that are poor in the dry season. It is a dual-use plant (forage and food) and its tops provide quality forage for livestock (Akundabwe et al., 1991). This study was carried out in this context to assess the nutritional values for livestock of five cowpea lines that were the subject of a recent agronomic evaluation study at the Saria experimental station (Barro et al., 2018). Specifically, this involves (i) determining the contents of the main chemical components of the leaves of the five cowpea lines in order to (ii) identify the best line for feeding ruminants.

Study Site
The study was carried out at the Saria and Kamboinsé research stations. 80 kilometres west of Ouagadougou, Saria is located. With geographical coordinates 12° 16' N and 2° 9' W, the climate is of a North Sudanese type (Guinko, 1984). The soil is a ferric lixisol (FAO, 1989), with an average depth ranging from 50 to 80 centimetres. This depth is limited by the presence of concretionated armour (Zougmoré et al., 2004).

Vegetal Material
Five cowpea lines, KVx745-11P, KVx771-10G (Nafi), KVx775-33-2G (Tilgré), BC3F10P34-1 and BC3F10P34-3, constituted the study plant material created by INERA. The first three lines are already popularized and the last two, which are the descendants of line KVx745-11P, are in the process of popularization. Table I shows the characteristics of the five cowpea lines.

Methodology Applied
Five cowpea lines were each manually sown in a well delineated block after ploughing, followed by the levelling and shelving of the experimental plot. Each lineage has been labelled in its block. Maintenance operations consisted of weeding, applying N14P23K14 fertilizer to the first weeding at 100Kg per hectare, and insecticide treatments. Two insecticide treatments were required, one at flower bud formation and the other at pod formation to protect flowers and pods. The insecticide used was titan at a dose of 2 ml per liter of water.
The following parameters were measured:  dry matter (DM) which is obtained by drying the sample in an oven at 105°C for 24 hours (AOAC method, 1990);  mineral matter (MM) or ash obtained by calcining MS in a muffle furnace at 550°C for 2 hours (AOAC method, 1990);  organic matter (OM) obtained by differentiating between DM and MM (AOAC method, 1990);  crude protein (CP) obtained by the conventional Kjeldahl method, which includes a step of mineralization with concentrated sulphuric acid and a distillation step, followed by titration of the distillates. The CP is estimated by applying to the percentage of nitrogen, the coefficient 6.25 conventionally accepted;  the parietal constituents, neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL) and crude fiber (CB) which are obtained by the method of Van Soest et al. (1991).

Statistical Analyses
The data collected were used to calculate the means (± standard deviation) before being subjected to a one-way analysis of variance (ANOVA) followed by the separation of the means obtained by the 5% Student Newman-Keuls test. The analysis of the bromatological values obtained shows that the lines studied are similar in terms of their dry matter (DM) content. The high MS rate would mean that the tops contain less water at the harvesting stage. According to Babatoundé (2005), ruminants must consume a certain amount of feed that must occupy a certain volume (the ingestion capacity), because the digestive tract only functions properly if it is sufficiently full. Thus, a sufficient amount of DM rich in energy can satisfy the needs of animals (Vandiest, 2005 The crude protein (CP) contents of the five lines (13.98 -17.47%) obtained in the study are above the minimum nitrogen content (7% DM) below which the rumen microflora cannot function efficiently (Kaboré-Zoungrana, 1995). These grades corroborate the results obtained by Ouattara (2015) with content higher than 15% at harvest, for KVx745-11P in pure culture and comparable to the 14% of Guiera senegalensis by Fall et al., (1997). These values are higher than those of Nourou (2014) and Diouf (1998) who found values of 12.18 to 13.09% and 11.10 to 16.09% respectively for other cowpea lines. They are also higher than the 3.85% of sorghum straws in Ouédraogo (1990), the 11.1% of groundnut vines and the 11.9% of cowpea vines obtained by Nantoumé et al., (2000). These values are higher than those of Nourou (2014) and Diouf (1998) who found values of 12.18 to 13.09% and 11.10 to 16.09% respectively for other cowpea lines. They are also higher than the 3.85% of sorghum straws in Ouédraogo (1990), the 11.1% of groundnut vines and the 11.9% of cowpea vines obtained by Nantoumé et al. (2000).

Results and Discussions
For cellulose, it is accepted that its use by ruminants is linked to the very functioning of the rumen and the richness of its population in microorganisms. The crude fiber (CB) contents of the five lines studied (26.45 to 31.85%) are comparable to those (29.20 to 33.60%) of Diouf (1998) on cowpea lines, to the 27.93% of P. reticulatum reported by Kiéma et al (2008) and to the 28.74% of C. obtusifolia reported by Wadré et al (2015).They are higher than those of Nourou (2014) who  . In general, lignins that are more or less strongly bound to parietal constituents are considered indigestible. As a physical barrier to microbial attack on the plant wall, they could cause a decrease in digestive efficiency in ruminants. It can then be assumed that the tops of the five lines studied, which were very poorly lignified at the harvesting stage, could therefore be digested entirely by ruminants to improve production.

Conclusion
This study highlighted the animal feeding potential of the fodder produced by the five cowpea lines at the Saria experimental station in Burkina Faso. All five lines, (KVx745-11P, KVx771-10G (Nafi), KVx775-33-2G (Tilgré), BC3F10P34-1 and BC3F10P34-3) have a good feed value for ruminants. However, BC3F10P34-3 would appear to be the best because it would contain more mineral material (13.49) and crude protein (17.47), and less fiber. By using this improved lineage, producers will benefit from a double interest, namely feeding their families (with seeds) and their ruminants (with fodder) in the dry season, a period of lack of quality fodder for ruminants. However, conservation techniques must be mastered in order not to distribute contaminated fodders to ruminants.