Marichal et al., 2010. Livest. Res. Rural Dev., 22 (2): 23

Differences in N fractionation, degradability of organic matter (OM) and N, forage adequacy for rumen microbial activity (estimated as the ratio between rumen available N and fermentable OM; RAN:FOM), and intestinal digestibility of rumen undegradable  protein (RUP) of birdsfoot trefoil, red clover, and alfalfa were evaluated. Within each legume specie, variations in phenological stages were studied. Nitrogen was partitioned into five fractions in accordance with  Cornell Net Carbohydrate and Protein System. Three fistulated cows were used to evaluate ruminal degradation (nylon bag technique), and RUP intestinal digestibility (mobile bag technique).   Legumes differed (P<0.004) in chemical composition. The potentially degradable fraction (PDF), degradation rate (kd), and effective degradability (ED) of OM and N were similar among species, and birdsfoot trefoil presented the smallest (P<0.05) soluble fraction (SF) of OM and N. The RAN: FOM ratio was similar in the three legumes, and  intestinal digestibility of N tended (P<0.06)  to be different among species.    Within each specie, a phenological stage effect (P<0.05) in chemical composition was detected. In the phenological stages evaluated, degradation kinetics of OM and N of the three legumes was similar. In birdsfoot trefoil and alfalfa, the EDOM and EDN were greater  (P < 0.04) in plants in vegetative stage than in bloom; meanwhile, in red clover the EDOM, but not EDN, was greater (P=0.023)  in vegetative stage. Vegetative forages tended (P < 0.06) to present the greatest RAN: FOM, and no phenological stages effect was detected in intestinal digestibility of RUP.   Results provide useful data for estimating protein supply to grazing ruminants. Research is needed to expand databases on N and OM characteristics of forages, in order to use accurately current feeding standards in grazing production systems.