Degradability of amino acids in selected legume forages using the in situ nylon-bag technique

Abstract

This study was conducted to determine the amino acid profiles and rumen degradability of amino acids of three cultivated forage legumes – velvet bean (Mucuna pruriens), cowpea (Vigna unguiculata) and silverleaf desmodium (Desmodium uncinatum) – using the in situ nylon-bag technique. Two Friesian cows fitted with 10-cm-diameter rumen cannulae on a complete dairy feed ration (19% crude-protein dairy meal and maize silage) were used. Silverleaf desmodium had significantly (p < 0.05) higher concentration of amino acids compared with cowpea and velvet bean. Aspartic acid showed the highest (p < 0.05) concentration in all legumes and cysteine showed the lowest concentration. Legume forage of cowpea showed the highest (p < 0.05) level of degradability of amino acid followed by silverleaf desmodium and then velvet bean. Readily and slowly degradable components in all amino acids were highest (p < 0.05) in cowpea followed by silverleaf desmodium and then velvet bean. Moreover, silverleaf and cowpea showed higher (p < 0.05) levels of effective degradability of amino acids (at outflow rates p = 0.02, 0.04 and 0.06 h⁻¹) than velvet bean. Total amino acid disappearance was the least in velvet bean, which suggests that it can be used to supply bypass protein to the duodenum of the ruminant animal.

Keywords: amino acids, forage legumes, rumen degradability