Abstract
Four varieties of common vetch, three improved varieties and one local variety, were evaluated for grain chemical composition, rumen protein degradability, and intestinal protein digestibility over two cropping years on the Tibetan Plateau. This study also examined correlations of grain chemical composition with rumen degradability parameters of grain protein and with intestinal digestibility of grain protein. Results of this study showed that grain quality attributes varied (p < 0.05) among varieties and cropping years. Significant intra-species variation was observed for concentrations (g/kg dry matter) of crude protein (CP; range = 347-374), ether extract (range = 15.8-19.6), neutral detergent fiber (aNDF; range = 201-237), acid detergent fiber (range = 58.2-71.6), ash (range = 27.6-31.0), effective CP degradability (EDCP; range = 732-801 g/kg CP), and intestinally absorbable digestible protein (IADP; range = 136-208 g/kg CP). The relationship between grain chemical composition and IADP was best described by the linear regression equation IADP = -0.828CP + 8.80ash + 0.635aNDF + 70.2 (R(2) = 0.891), indicating that chemical analysis offers a quick and reliable method for IADP of common vetch grain. In terms of EDCP and IADP of grain, common vetch varieties, Lanjian No.2 and Lanjian No. 3, have the greatest potential among varieties tested for supplementing ruminant diets when grown on the Tibetan Plateau.