EFFECTS OF TROPICAL BROWSE PLANTS ON IN VITRO RUMEN PROTEIN DEGRADABILITY

Abstract

Leaves of Multi-purpose trees (MPT) provide a very important ecosystem service in the form of feed for ruminant livestock in most tropical countries. They are often fed to ruminants as supplements due to their appreciable levels of crude protein and less concentration of recalcitrant cell wall fiber.The presence of condensed tannins in tropical MPT could minimise protein degradation in the rumen, reduce rumen ammonia concentration and ultimately reduce overall dry matter digestibility. In this study, eight MPT (Ceiba pentandra, Khaya senegalensis, Senna siamea, Ficus gnaphalocarpa, Pterocarpus erinaceus, Albizia lebbeck, Azadirachta indica and Gmelina arborea) were incubated with two levels of nitrogen to test the effect of condensed tannin on in vitro ammonia nitrogen concentration. The MPT’s in another experiment were incubated in sacco to determine the extent of protein degradability. The crude protein (CP) of the MPT was in the range of 92.2 to 229 g/kg DM. The neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) were in the range of 216-307 g/kg DM, 163.4 to 291 g/kg DM and 94.8-282 g/kg DM respectively. The highest condensed tannin (CT) was obtained in F gnaphalocarpa with no CT detected in A Lebbeck. There was no effect of the MPT and nitrogen buffer interaction on the in vitro gas production parameters at 72 h. There was no difference in in vitro dry matter digestibility (IVDMD) between the two nitrogen (N) buffered rumen fluids. Leaves of MPT incubated in nitrogen sufficient (NSf) buffer consistently had a higher NH3N concentration than the nitrogen deficient (ND). However, the NH3N concentration from the ND buffer remained within levels that ensured IVDMD was not different from that of NSf. The in sacco CP degradation characteristics differed among the leaves at 72 h. A. indica had a higher proportion of its protein content being soluble. The MPT with CT had lower proportion of their protein being degraded particularly in C. pentandra. Ammonia nitrogen concentration was maintained within limits that did not negatively affect IVDMD when the leaves of the MPT were incubated in ND and Nsf.