![Sample our Environment & Agriculture journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5934/TOC-Subject-Sample-2021-Environment-Agriculture.jpg"})
Abstract
The effects of regular implantation of 36 mg zeranol on behaviour, growth rate, and carcass characteristics of young Friesian bulls grazing grass pastures in New Zealand were evaluated. The trial, involving 206 bulls, compared 2 implanting intervals of 70 days and 105 days with untreated controls over a 420 day period, starting at an average weaning age of 12 weeks. A newly developed objective assessment of behaviour (RYDER score) demonstrated (P<0.001) that zeranol-treated animals exhibited less than 25% as much riding as untreated animals, depending on the initial implanting weight. In addition, bulling activity in treated animals was reduced by a factor of 3. Bulls implanted every 70 days showed a significant (P<0.05) increase in mean liveweight gain of 12.4 kg (4.8%) compared with unimplanted bulls. Those implanted every 105 days showed no significant liveweight response. Treated animals exhibited improved hindquarter development and weight of tenderloin steaks. It is concluded that the behaviour-controlling effect of implanting with zeranol, combined with improved weight gain and carcass characteristics, will enable increased use of entire bulls for efficient beef production.