Use of a β-Agonist to Alter Fat and Muscle Deposition in Steers1

Abstract

The effect of a β-agonist, clenbuterol [benzyl alcohol, 4-amino-α-(t-butylamino)methyl-3, 5-dichloro] on carcass composition, performance criteria and clinical blood chemistry was evaluated in 24 finishing Hereford steers assigned to three treatment groups. Clenbuterol was administered in the feed at 0, 10 or 500 mg•head−1•d−1 for 98 d. Carcass evaluation showed that the 10 and 500 mg•head−1•d−1 treatment groups had 11 (P≤.05) and 16% (P≤.01) larger 12th rib longissimus muscle areas, 35 (P≤.01) and 42% (P≤.01) less 12th rib fat depths, 23 (P≤.05) and 33% (P≤.01) less kidney, pelvic and heart fat and improved USDA yield grades of 1.0 and 1.5 grade points, respectively. Chemical analysis of the 9th to 11th rib section from these carcasses indicated that they had 13 (P≤.01) and 14% (P≤.01) higher protein contents, 20 (P≤.01) and 30% (P≤.01) less fat and 10 (P≤.05) and 16% (P≤.01) more water, respectively. Clinical chemistry measurements were within normal physiological ranges. Blood urea N levels (mg/dl) for the 0, 10 and 500 mg clen-buterol•head−1•d−1 were 9.6, 8.5 and 5.9 (P≤.01), respectively, indicating that clenbuterol may have increased N retention. Rate of gain was not altered at 10 mg•head−1•d−1, but was reduced (P≤.05) by the high drug level. There were no differences among treatments in feed efficiency. The data demonstrate that significant improvements in muscle accretion with concomitant reductions in fat deposition can be achieved by feeding clenbuterol to finishing steers.