Effect of duration of a beta-agonist treatment on growth, feed intake and carcass characteristics in finishing bulls.

Two experiments were conducted to study the effect of a different duration of dietary cimaterol on animal performances and carcass characteristics in finishing Belgian White-blue bulls. They received a concentrate diet ad libitum during 228 days on average, containing no cimaterol (control) or 4 ppm cimaterol during 71, 127 or 246 days (experiment 1) or during the last 76, 108 or 136 days before the end of the fattening period (experiment 2). Prior to slaughter a 6-day withdrawal period was applied. There was a significant increase in the growth rate immediately after the onset of the cimaterol feeding. A long-term cimaterol administration of 4.5 to 8 months tended to decrease daily gain towards the end of the experiment. Average daily feed intake was only slightly reduced when cimaterol was fed from the beginning of the experiment. Feed conversion was improved by cimaterol, but the effect was smaller after a long-term administration. Increased Longissimus dorsi area and hindleg width revealed muscle hypertrophy in cimaterol-treated bulls. Dressing percent and carcass meat content were increased. Optimum duration of 4 ppm dietary cimaterol varied between 2.5 and 4 months.