Reference

Response to ractopamine-hydrogen chloride is similar in yearling steers across days on feed

All Rights Reserved. Response to ractopamine-hydrogen chloride is similar in yearling steers across days on feed. Winterholler, S. J.; Parsons, G. L.; Reinhardt, C. D.; Hutcheson, J. P.; Nichols, W. T.; Yates, D. A.; Swingle, R. S.; Johnson, B. J. (Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506, USA). Journal of Animal Science (Savoy, IL, United States), 85(2), 413-419 (English) 2007 American Society of Animal Science. CODEN: JANSAG. ISSN: 0021-8812. DOCUMENT TYPE: Journal CA Section: 1 (Pharmacology) Yearling steers (n = 2,552; 314 kg of initial BW) were used to evaluate the effects of ractopamine-HCl (RAC) and days on feed on performance, carcass characteristics, and skeletal muscle gene expression in finishing steers. Treatment groups included serial slaughter dates of 150, 171, or 192 d on feed. Within each slaughter date, steers either received RAC (200 mg/steer) daily for the final 28 d or were not fed RAC. All steers were initially implanted with Revalor-IS and were reimplanted with Revalor-S after 75 d on feed. At slaughter, muscle samples from the semimembranosus were collected for mRNA anal. of the b-adrenergic receptors (b-AR). Ractopamine administration increased (P < 0.05) ADG, G:F, and HCW and increased (P = 0.08) LM area. Ractopamine did not affect the dressing percentage, USDA yield grade, or quality grade (P > 0.3). There was no change in overall feed intake across the entire feeding period; however, feed intake was increased during the 28-d period during which the steers were fed RAC (P ￡ 0.05). Greater days on feed decreased (P < 0.05) ADG, G:F, DMI, and the no. of yield grade 1 and 2 carcasses. Also, greater days on feed increased (P < 0.05) HCW, dressing percentage, and the no. of prime and choice carcasses, as well as the no. of yield grade 4 and 5 carcasses. Increasing days on feed decreased (P < 0.05) the abundance of b1-AR and b3-AR mRNA and increased (P < 0.05) the abundance of b2-AR mRNA in skeletal muscle samples obtained at slaughter. Ractopamine had no effect (P > 0.10) on the abundance of b1-AR or b3-AR mRNA, but tended (P = 0.In this experiment, several chemicals are used like 90274-24-1 09) to increase b2-AR mRNA. Addnl. time-course studies with primary muscle cell cultures revealed that advancing time in culture increased (P < 0.001) b2-AR mRNA but had no effect (P > 0.10) on b1-AR or b3-AR mRNA. We conclude that days on feed and RAC are affecting b-AR mRNA levels, which could, in turn, impact the biol. response to RAC feeding in yearling steers. .