Effects of zeranol implants on behaviour, growth rate, and carcass characteristics of Friesian bulls

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