DIGESTIBILITY OF ADDITIONAL CRUDE PROTEIN FROM TROPICAL LEGUMES IN MIXED GRASS-LEGUME RATIONS FOR RUMINANTS

Abstract

The digestibility of crude protein (CP) from tropical legumes in grass-legume mixed diets was studied based on literature data by regressing the digestible CP (digCP) on the proportion of CP from legumes in the diet. In vivo studies reporting on CP concentration and in vivo CP digestibility values of ruminants fed diets with tropical legumes and grasses with no other feed, were selected for the analysis (56 publications, 213 dietary treatments (150 legume forages, 63 grasses)). First, observations were classified into categories based on the CP concentration of the control grass using the first and the third quartile of the grass CP concentration (LOW, MEDIUM, and HIGH grass quality). Second, legumes were divided based on their growth habit: herbs, shrubs, and trees. Based on the slopes and coefficients of the regressions of the digCP supply on the proportion of CP from legumes, CP digestibility of legumes was higher than that of LOW quality grasses, but lower than that of MEDIUM and HIGH quality grasses. Furthermore, the digestibility of the additional CP from legumes was higher when combined with MEDIUM quality grasses (0.493) compared with those of LOW quality (0.432), while it decreased when combined with HIGH quality grasses (0.305). No differences appeared in the digestibility of additional CP from legumes depending on their growth habit (range 0.415 to 0.421). These results can help optimize the assimilation of CP supplemented by tropical legumes.