The effects of ractopamine-HCl (Optaflexx) on performance, carcass characteristics, and meat quality of finishing feedlot heifers

¹ Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-1600

^* To whom correspondence should be addressed. E-mail: jdrouill{at}ksu.edu.

	Abstract

Two experiments were conducted at the Kansas State University Beef Cattle Research Center to determine effects of Ractopamine-HCl (Optaflexx, Elanco Animal Health, Greenfield, IN) on growth performance, carcass characteristics, and meat quality of finishing feedlot heifers. In Exp. 1, heifers implanted with Revalor-H (n = 302, initial BW = 479 kg,) were fed steam-flaked corn diets with 0 (CON) or 200 mg ractopamine-HCl (OPT) per heifer daily for 28 d prior to slaughter. Average daily gain and DMI were not different between treatments (P > 0.17); however, OPT cattle tended to be more efficient (P = 0.06). Treatments did not differ with respect to final BW, HCW, dressing percentage, USDA yield grade, USDA quality grade, marbling score, LM area, KPH, Warner-Bratzler shear force, weight loss during cooking; L* , a*, and b* colorimetric values during a 7-d retail display; or purge loss from loin steaks during retail display (P > 0.19). In Exp. 2, non-implanted crossbred heifers (n = 281, BW = 451 ± 2 kg) were fed finishing diets based on steam-flaked corn. A control diet (CON; no ractopamine) was compared to diets providing 200 mg OPT per heifer daily for periods of 28 or 42 d (200 x 28 and 200 x 42, respectively); 300 mg/d for 28 d (300 x 28); and a step-up regimen consisting of 14 d at 100 mg, followed by 14 d at 200 mg, and the final 14 d at 300 mg (Step-up). Feeding OPT had no effect on carcass weight gain among treatments (P = 0.18). Efficiency of carcass gain was 34% and 35% greater (P = 0.06) for 200 x 42 and Step-up when compared to control, respectively. Feeding OPT at 300 mg for 28 d reduced DMI compared to CON, 200 x 28, and 200 x 42 (P < 0.05). Administration of OPT had no effect on marbling score, yield grade, LM area, KPH, or percentages of carcasses grading USDA Choice (P > 0.10). Feeding ractopamine-HCl to finishing heifers generally improved carcass gain efficiency with minimal impact on carcass characteristics. These effects were most pronounced in heifers fed ractopamine for 42 d.

Key Words: ractopamine-HCl, beef cattle, heifers