Effect of the beta-adrenergic agonist cimaterol (CL 263,780) on the growth and carcass characteristics of finishing swine.

A randomized complete-block design was used to evaluate the effects of the beta-adrenergic agonist, cimaterol (CL 263,780), on growth rate, feed efficiency and carcass composition of finishing swine. The drug was fed at four levels (0, .25, .5 and 1.0 ppm) to a total of 240 pigs from 64.5 to 103.7 kg live weight. Growth rate and feed efficiency were measured during the 7-wk feeding trial. Feeding cimaterol depressed feed intake, improved feed efficiency and did not alter rate of gain. Carcass evaluation showed that pigs continuously fed cimaterol had 13.2, 9.3 and 9.2% less fat measured at the 10th rib, P2 and average backfat (BF) locations, respectively, compared with controls. Cimaterol-fed pigs had increased loin eye areas (10.9%), and increased semitendinosus (11.8%) and biceps femoris (8.9%) weights compared with controls. The semitendinosus muscles of the cimaterol-fed pigs had less fat and the femur bones were shorter and lighter weight than controls. There were no detected differences in structural soundness of the live pigs, but postmortem evaluation of the hooves indicated that pigs fed 1.0 ppm cimaterol had a higher incidence of hoof lesions. Pigs withdrawn from cimaterol for 7 d were comparable in performance and carcass characteristics with those continuously fed the drug except that carcass fat measurements had generally returned to control values. The data indicate that cimaterol improved the feed efficiency of finishing pigs and increased the lean:fat ratio of their carcasses. Withdrawal of cimaterol caused compensatory fat deposition.