Chemical composition and in vitro ruminal fermentation characteristics of cowpea varieties in the Limpopo Province, South Africa

Abstract

Shortage of quality feed is the major constraint in livestock production particularly under smallholder subsistence farmer’s conditions in sub-Saharan Africa, including South Africa. This is due to the fact that livestock production under smallholder subsistence farmers predominantly depends on communal grazed natural pastures which are often inadequate in both quality and quantity particularly during the dry season. In order to improve livestock production in these areas, there is a need to address shortage of feed both in terms of quantity and quality. Consequently cowpea (Vigna unguiculata (L.) Walp.) varieties adaptable in Limpopo province of South Africa were evaluated for their nutritive value and in vitro gas production (fermentation) attributes in order to identify superior varieties as potential forage source for ruminants animals. Several laboratory experiments (including proximate analysis, in vitro digestibility estimate and gas production) were conducted at the University of Pretoria, South Africa. In this study, 12 varieties of cowpea were evaluated for their chemical composition, in vitro organic matter digestibility and gas production (fermentation) attributes. Generally the adaptable varieties had more than 15% crude protein (CP) content with relatively low neutral detergent fibre (NDF), thus they were highly digestible. This indicates that these varieties could be potentially utilised as supplementary forage and nitrogen source to complement poor quality forage. However, of the 12 varieties, three, Bechuana white, IT 97K-499-35 and TX 08-30-1 were relatively superior as they had greater CP, ME and IVOMD with low fibre values. Hence, these three varieties are chosen for further evaluation in terms of their potential in improving ruminal fermentation and digestibility of poor quality grass hay when used as supplement at three different levels of inclusion. This was done by conducting an in vitro gas production experiment and measuring parameters such as, ruminal fermentation, in vitro organic matter digestibility and NDF degradability of forage. Generally supplementing poor quality grass hay with cowpea varieties improved grass hay fermentation. Among the cowpea varieties, high levels of inclusion resulted in greater gas production for Bechuana White and IT 97K-499-35, while for TX 08-30-1 variety, there was no difference between 15 vs 30 % or 50% inclusion level. Thus Bechuana White and IT 97K-499-35 can be used as a forage source while TX 08-30-1 varieties can be recommended as a protein source to supplement poor quality forage. However, there is a need to determine their dry matter intake, digestibility and animal performance response in order to utilise them in the feeding system of ruminants. In vitro supplementary results to poor quality forage suggests that thirty percent level of inclusion of the two cowpea varieties (Bechuana White and IT 97K-499-35) has the maximum benefit.