Voluntary intake, nitrogen metabolism and rumen fermentation patterns in sheep given cowpea, silverleaf desmodium and fine-stem stylo legume hays as supplementary feeds to natural pasture hay

Abstract

The effect of feeding legumes as protein supplements to veld hay on voluntary feed intake, nitrogen metabolism and rumen fermentation patterns was evaluated. Four sheep were randomly allocated to the four dietary treatments of either veld hay alone or veld hay supplemented with either cowpea, fine-stem stylo or silverleaf desmodium. Total dry matter intake was highest with cowpea (P < 0.05), and the lowest increment (P < 0.01) was with silverleaf desmodium. The pH of the rumen fluid was lower (P < 0.01) in sheep given the supplemented diets than the veld hay alone. The cowpea-supplemented diet produced higher (P < 0.05) levels of ammonia N than the other diets. The silverleaf desmodium diet produced the highest level of total volatile fatty acids (VFA) (P < 0.05). Supplementation with the legumes improved the nitrogen retention, although animals on all treatments were in negative nitrogen balance. Legume supplementation to the veld hay also enhanced rumen fermentation, as reflected by an increase in ruminal ammonia N and VFA concentrations. These results suggest that although the legume hay increased dry matter and nitrogen utilisation, the negative nitrogen retentions might indicate the inadequacy of the specific legume hays used as nitrogen supplementary feeds to sheep fed a basal diet of veld hay.