Degradation of tropical roughages and concentrate feeds in the rumen

Abstract

Degradation characteristics of four grasses, three leguminous fodder species, jack leaves, coconut meal and rice bran were studied using the nylon bag procedure. Bag incubations up to 10 days were performed in the rumen of cows fed on a ration consisting of 50% wheat straw and 50% hay. Degradation characteristics for organic matter (OM), neutral detergent fibre (NDF) and nitrogen (N) were evaluated using a two fraction model with a fixed undegradable fraction ( U) and lag time. Among the grasses, the degradable fractions ( D) of OM and NDF in NB21 and guinea grass were significantly higher ( P < 0.05) than in the other two grasses. Guinea grass not only had the highest N content (20.3 g kg −1 dry matter (DM)), but also its D fraction was significantly higher ( P < 0.05) than that of the other grasses. The rate of degradation ( k d) for all components studied did not differ significantly between grasses. Unlike in grass species, the D and U values obtained for OM, NDF, and N in legumes species did not differ significantly, but the k d values were significantly ( P < 0.05) different. Except for the long lag phase in jack leaves, which ranged from 10.4 h for NDF to 11.5 h for N, all other degradation characteristics were significantly higher ( P < 0.05) than for grasses and rice bran. The poor nutritive value of rice bran obtained from a commercial mill was reflected in the extremely high U fraction (47%, 66% and 22% for OM, NDF and N, respectively). Nevertheless, the degradation characteristics ( D and k d) for N were significantly better than for grasses. Coconut meal had the highest potentially degradable fraction ( D + water soluble fraction). Rumen degradable N content in grasses ranged from 41% (guinea) to 60% (ruzi), and in legumes from 69% (leucaena) to 79% (glyricidia). About 67% of the N present in jack leaves and rice bran was rumen degradable.