Effects of supplemental amino acids or protein on forage utilization and animal performance

Abstract

Four experiments were conducted to study the effects of supplemental amino acids or protein on forage utilization and animal performance. Heifers with ruminal and duodenal cannulae grazed cool-season or warm-season pastures and were randomly assigned to different levels of rumen-protected methionine (Exp. 1), rumenprotected lysine (Exp. 2) or undegraded intake protein (Exp. 3). Digesta flow and fecal output were determined by reference to daily dosed markers in fecal and duodenal samples. Turnover rates, organic matter and indigestible NDF fill from different feeds were determined by reference to pulse dosed markers. Intake was estimated by reference to fecal output and digestibility using indigestible NDF as an internal marker. In Exp. 1, level of rumen-protected methionine had no effect (P > .05) on forage intake or utilization. Thus, methionine may not be the metabolizable nutrient first limiting performance and forage utilization in calves grazing cool-season grasses. In Exp. 2, level of rumen-protected lysine did not affect (P > .05) forage intake and utilization in calves grazing bermudagrass. Lysine does not seem to be a limiting nutrient in calves grazing warm-season grasses. In Exp. 3, level of undegraded intake protein did not show any effect on forage intake and utilization by calves grazing bermudagrass and suggests that these calves were not deficient in escape protein. In Exp. 4, no response (P > .05) in liveweight gain was found due to different protein supplements or to two different methionine sources in calves grazing bermudagrass. Ruminal turnover of supplement residues was faster than that of forage residues for calves grazing bermudagrass or ryegrass (P > .05). Ruminal turnover of ryegrass residues was faster (P < .05) than that of bermudagrass. Calves on ryegrass had less rumen organic matter fill and shorter rumen retention time when compared to those on bermudagrass. Supplement residues for calves on ryegrass had a faster r-uminal turnover as compared to residues from bermudagrass. Compartmental residence time of the mixing system differed (P < .05) whether the sampling was conducted at the duodenum or rectum on both grasses, contradicting the idea that most of the mixing process occurs in the rumen. grasses. In Exp. 2, level of rumen-protected lysine did not affect (P > .05) forage intake and utilization in calves grazing bermudagrass. Lysine does not seem to be a limiting nutrient in calves grazing warm-season grasses. In Exp. 3, level of undegraded intake protein did not show any effect on forage intake and utilization by calves grazing bermudagrass and suggests that these calves were not deficient in escape protein. In Exp. 4, no response (P > .05) in liveweight gain was found due to different protein supplements or to two different methionine sources in calves grazing bermudagrass. Ruminal turnover of supplement residues was faster than that of forage residues for calves grazing bermudagrass or ryegrass (P > .05). Ruminal turnover of ryegrass residues was faster (P < .05) than that of bermudagrass. Calves on ryegrass had less rumen organic matter fill and shorter rumen retention time when compared to those on bermudagrass. Supplement residues for calves on ryegrass had a faster ruminal turnover as compared to residues from bermudagrass. Compartmental residence time of the mixing system differed (P < .05) whether the sampling was conducted at the duodenum or rectum on both grasses, contradicting the idea that most of the mixing process occurs in the rumen.