Seasonal growth and carcass characteristics of grazing steers implanted with trenbolone acetate and oestradiol

Abstract

Measurements were made of the effects of Revalor on the seasonal growth, carcass weight and fatness of Zebu crossbred steers in central Queensland. Ninety-three steers were grazed on improved pastures for 15 months prior to slaughter. Half the animals were implanted with Revalor (140 mg trenbolone acetate plus 28 mg oestradiol-17B mixed with cholesterol) for the first 25 weeks (September-March) and the balance left as controls. During this period, treated steers gained weight significantly (P<0.001) faster than untreated steers (0.57 v. 0.42 kg/day). In March, the 2 groups were further divided into 2 subgroups and 1 subgroup from each group was either implanted for the first time or reimplanted with Revalor. The animals implanted in March were reimplanted again 4 months later. The other subgroups were not implanted. After implantation in March, steers implanted for the first time gained weight significantly (P<0.001) faster (1.27 kg/day) than all other treatment groups. Steers implanted at the beginning of the experiment in September, but not reimplanted in March, continued to gain significantly (P<0.05) faster in the period March-May than steers which had never been implanted (1.01 v. 0.85 kg/day). This suggests that the implant was still having an anabolic action at least 6 months after implantation. The experiment ended with the slaughter of the steers in December. Animals treated with Revalor at some time during the experiment were significantly (P<0.05) heavier at slaughter (about 22 kg) and had significantly (P<0.001) heavier carcasses (about 13 kg) than those left untreated. Steers implanted throughout the experiment and those implanted for the 9 months before slaughter had significantly (P<0.001) less subcutaneous fat at the P8 rump site than those either not treated or implanted earlier than 9 months prior to slaughter.