Effects of dietary tallow containing trace amounts of ractopamine on beef cattle performance and tissue residue levels and the effect of withdrawal time on ractopamine residues in the gastrointestinal-tract digesta

Abstract

The objectives of these experiments were to evaluate (1) if inclusion of inedible tallow containing ractopamine (RAC) in the cattle diet influences feedlot performance, carcass characteristics, and results in detectable RAC in tissues and (2) the effect of withdrawal time on RAC residues in the gastrointestinal-tract digesta of cattle. In Exp. 1, beef steers (n = 28) were assigned to dietary treatments formulated with feed tallow ranging from 100% inedible tallow to 100% technical tallow. After 91 d, steers were transported to a commercial abattoir and slaughtered, and tissues were collected for RAC analysis. In Exp. 2, steers fitted with ruminal and duodenal cannulas were assigned to the control group (no RAC) or a group in which RAC was supplemented at 400 mg of RAC∙animal −1 ∙d −1 for 28 d. On d 29, RAC supplementation was withdrawn. Daily ruminal, duodenal, and fecal samples were obtained for RAC analysis beginning 3 d before RAC withdrawal and continuing to d 13 after withdrawal. No treatment effects of dietary inedible tallow inclusion was observed for final BW ( P < 0.67), ADG ( P < 0.70), DMI ( P < 0.26), feed efficiency (G:F; P < 0.48), hot carcass weight ( P < 0.26), DP ( P < 0.24), or YG ( P < 0.32). However, RAC was detected in abomasum and fat tissues. By the end of the 10-d withdrawal period, RAC concentrations in all samples from treated steers were numerically similar to controls, and RAC was detectable in all samples, including controls, at all time points measured. The results indicate that RAC residue in feed tallow does not affect animal performance or carcass characteristics. Detectable RAC in sampled tissues and gastrointestinal digesta suggests a need for further investigation of RAC residues to maintain compliance for exported beef products.