Variation in protein degradability in dried forage legumes

Abstract

Proteins in forage legumes are rapidly degraded in the rumen, inducing a poor dietary protein efficiency, risk of bloat, and nitrogen loss detrimental to the environment. The aim of this study was to investigate the variation in ruminal protein degradability among legume species and cultivars. Four species, each represented by 1 to 16 cultivars, were studied: lucerne (Medicago sativa), white clover (Trifolium repens), birdsfoot trefoil (Lotus sp.) and crownvetch (Coronilla varia). In a first experiment, forage samples of 16 cultivars of lucerne harvested in the autumn of 1998 were incubated in nylon bags in 3 fistulated cows in order to obtain the kinetics of ruminal degrada- tion of crude protein and dry matter. The phenotypic variation in crude protein degradation was not significant, and was partly related to the dry matter degradation. In a second experiment, lucerne (5), birdsfoot trefoil (5), white clover (4) and crownvetch (1) cultivars were harvested in two cuts in 2000, and dry matter and crude protein degradation were analysed at 3 incubation times (2, 8 and 48 h) in the rumen of the fistulated cows. Crude protein degradation was higher for lucerne than for white clover, and these two tannin-free species exhibited greater crude protein degradation than crownvetch and birdsfoot trefoil. In birdsfoot trefoil, crude protein degradation was negatively correlated to con- densed tannin content but positively correlated to dry matter degradation. Except for birdsfoot trefoil, the range of genetic variation within species for in situ crude protein degradation was low.