Chemical composition of Lablab purpureus and Vigna unguiculata and their subsequent effects on methane production in Xhosa lop-eared goats

Abstract

The objective of this study was to evaluate the nutritive value and anti-nutrient contents of Lablab purpureus (Lablab) and Vigna unguiculata (cowpea) and their effects on methane production in goats. Legume forages were grown and harvested at three stages of growth of pre-anthesis, anthesis, and post anthesis. Samples were collected at each stage and examined for proximate composition, total phenolics, condensed tannins, and saponins using standard methods. Hay was harvested at the anthesis stage and used in a growth study to evaluate the effects of forage legumes on methane production. Eighteen one-year-old goats, nine males and nine females, were used in the feeding trial. The goats were subjected to three treatment diets with six goats in each treatment, representing both sexes equally, for 60 days in a complete randomized design. Methane was measured with a laser methane detector (LMD). Cowpea showed higher ash (13.11%), acid detergent fibre (ADF) (38.42%), and crude protein (CP) (20.23%) than Lablab, which had values of 11.45 %, 36.17%, and 19%, for ash, ADF, and CP, respectively. Lablab had significantly higher fat content (2.41%), neutral detergent fibre (NDF) (49.27%), and hemicellulose (13.07%) than cowpea (2.1%, 46.91%, and 8.48%, respectively). The tannin, phenolic, and saponin content were influenced significantly by forage species and stage of growth. The diet and sex of the animal affected enteric methane production significantly. Forage legumes met animal requirements for fat, ADF, NDF, and CP. The energy and tannin levels of forage legumes were shown to reduce enteric methane production in goats.

Keywords: Forage legumes, nutritive value, small ruminants