Effects of supplemental rumen stable methionine and lysine on growing calves grazing bermudagrass or ryegrass pastures

Abstract

A series of four experiments were conducted to assess the effects of supplemental amino acids on animal performance and forage utilization. European crossbred yearling steers (Exp. 1) and Brahman crossbred heifers (Exp. 2) grazed ryegrass pasture, and Brahman crossbred heifer calves (Exp. 3 and 4) grazed bermudagrass (Exp. 3) and fed bermudagrass hay ad libitum (Exp. 4). Animals were randomly assigned to different levels of rumen stable methionine and lysine (Exp. I and 3) or rumen stable methionine (Exp. 2 and 4) in a randomized complete block design. Animal performance was estimated from shrunk weight at the beginning and end of each experiment. Estimates of requirements and supply of methionine and lysine were calculated in each of the four experiments. In Exp. 3, fecal output was estimated by reference to daily dose markers in output was estimated by reference to daily dose markers in fecal samples. Intake was also determined in Exp. 3 by reference to fecal output and digestibility using indigestible NDF as an internal marker. In Exp. 1, level of rumen stable methionine and lysine did not affect (P = .96) average daily gain (1.52 kg/d) of steers grazing ryegrass. In Exp. 2, level of rumen stable methionine did not affect (P = .40) average daily gain (.81 kg/d). In Exp. 3, level of supplemental methionine and lysine did not affect (P > .05) forage intake, forage utilization, or animal performance of calves grazing bermudagrass. In Exp. 4, the average daily gain of heifers fed bermudagrass hay did not differ (P = .77) due to supplementation with different levels of rumen stable methionine. Supplementation with rumen stable methionine or methionine-lysine combinations did not increase average daily gain of animals grazing ryegrass or bermudagrass, or fed bermudagrass hay. This indicates that neither methionine or lysine were limiting nutrients for the growing cattle used in these trials.