Effect of synthetic hormone implants on grazing steers in Queensland

Abstract

Data are presented on the effect of hormone implants in fattening beef cattle on 10 properties at various centres in Queensland. Sixteen different trials involving observations on 377 treated animals and 295 control animals have been conducted. All but one trial involved grazing animals.
Excluding one trial concerning the effect of implantation on growing animals, a significant response in growth rate was obtained in 12 out of the remaining 15 trials. The overall response to treatment was statistically highly significant and ranged from 0.14 to 0.72 lb per animal daily over the final fattening period.
There were no significant differences in response to levels varying from 15 mg to 60 mg hexoestrol.
A significant positive relationship exists between response of treated animals and growth rate of the controls.
No significant difference was detected between the growth rate of the treated and control animals in the growing state, but the number in each group was small. There is an indication of faster growth by treated animals in the three to four months following implantation.
Condition grade did not appear to be related to magnitude of response.
Conformation defects appeared in treated animals apparently without causing a downgrading of carcasses.
Dressing percentage of treated and control groups did not differ significantly.
Eye muscle depth was significantly greater in the treated animals.
Treated animals had significantly less fat cover over the eye muscle. In one trial a considerable downgrading of carcasses was due mainly to insufficient fat cover in the treated groups at the 30 mg and 60 mg levels.
No significant differences between carcasses were detected by the methods of appraisal which were employed.