Effects of supplementary inosine on nutrient digestibility, ruminal fermentation and nitrogen balance in goats fed high amount of concentrate

A study was conducted to compare responses of nutrient intake, digestibility, ruminal fermentation, and N balance in goats fed high amounts of concentrate supplemented with inosine or urea. Four Japanese Saneen goats (49.2 ± 5 kg), housed in individual metabolic cages, were blocked by weight into two pairs, and assigned inosine or urea as non-protein N (NPN) supplements to their basal diet at 0.15 g per kg body weight on a urea basis, in a 2 × 2 switch back experimental design. The basal diet consisted of 0.4 timothy hay, and 0.6 concentrates, and was fed to the goats as a total mixed ration (TMR). The experimental period was 13 days, including 7 days of adaptation, 5 days of sampling of feces, urine and orts, and 1 day of sampling of rumen fluid. Intake of dry matter (DM), organic matter (OM), neutral detergent fiber (NDF) and crude protein (CP) and digestibility in the total tract, as well as N balance, were assessed by total fecal collection. Rumen fluid was sampled at 0, 1, 4 and 7 h after feeding, and analyzed for pH, ammonia and volatile fatty acids (VFA). Additionally, samples collected at 0 and 4 h after feeding were assessed for protozoal counts. Daily intakes of DM, OM, NDF and CP did not differ among treatments. Digestibility in the total tract tended (P=0.07) to be lower for NDF and was numerically lower for DM (P=0.11), OM (P=0.11), and NDF (P=0.12) in goats supplemented with inosine versus urea. Ammonia concentration and ruminal pH were similar among treatments, and protozoal counts 4 h after feeding was lower (P=0.02) in goats supplemented with inosine compared to those on urea. No differences between treatments occurred in concentrations of rumen VFA (i.e., acetate, propionate, valerate, iso-acids, and total VFA) except for butyrate, which was higher (P=0.03) in goats supplemented with inosine versus urea 4 h after feeding. There were no differences in intake, absorption and retention of N between treatments. Thus, responses in nutrient intake, digestibility, ruminal fermentation and N balance in goats fed high amounts of concentrate with supplementary inosine and urea were similar.