Evaluation of protein degradation characteristics and metabolisable protein of elephant grass (Pennisetum purpureum) and locally available protein supplements

Abstract

Degradation characteristics of crude protein (CP) and metabolisable protein (MP) of feeds for early-weaned, growing and finishing beef bulls were evaluated in three experiments. Feeds in experiment 1 were fresh elephant grass (FEG) and molasses supplemented with sweet potato vines (SPV) in diet 1, supplemental (GCM) compounded from gliricidia, cottonseed cake (CSC), maize bran and NaCl in diet 2 and a commercial concentrate (CC) in diet 3. Feeds in experiment 2 were basal maize stover mixed with molasses (MSM) and FEG supplemented with SPV in diet 1, GCM in diet 2 and CC in diet 3. In experiment 3, MSM and FEG were supplemented with compounded supplemental protein feeds with varying levels of gliricidia inclusion. Supplemental (GM) containing gliricidia, maize bran and NaCl were used in diet 1, GCM in diet 2 and supplemental (CM) containing CSC, maize bran and NaCl in diet 3. Degradabilities of experimental feeds were measured at 0, 6, 12, 24, 48, 72, 96, and 120 h by the nylon bag technique using two rumen fistulated steers (300±10 kg). Effective CP degradabilities of FEG in the three experiments varied (P<0.05) with the supplements. In experiment 1, effective CP degradabilities of the supplements varied (P<0.05) from 668.3 g kg⁻¹ CP in CC to 722.1 g kg⁻¹ CP in SPV and 743.7 g kg⁻¹ CP in GCM. Effective rumen degradable protein (ERDP), digestible udegradable protein (DUP) and MP varied (P<0.05) among the supplements. In experiment 2, effective CP degradabilities of the supplements did not vary but ERDP varied (P<0.05) from 83.7 g kg⁻¹ CP in SPV to 116.6 g kg⁻¹ CP in GCM and 123.8 g kg⁻¹ CP in CC and MP followed similar trends. In experiment 3, effective CP degradabilities of the supplements decreased (P<0.05) with increasing gliricidia inclusion. ERDP increased (P<0.05) with lower gliricidia while DUP varied (P<0.05) from 18.2 g kg⁻¹ CP in CM to 23.6 g kg⁻¹ CP in GCM and 36.6 g kg⁻¹ CP in GM. These data have shown that the majority of locally available feeds evaluated in this study are not similar in CP degradation characteristics and MP but compounded GCM is more suitable in providing degradable and undegradable protein for beef bulls in Uganda.