Implantation of oestrogenic hormones in beef cattle

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Abstract
A comparison was made of growth responses to autumn- versus spring-implantation of 20 mg oestradiol benzoate plus 200 mg progesterone (8 pellets) in 20-month-old, Aberdeen Angus, pasture-fed steers. Both autumn and spring hormone tr~atment led to marked increases in growth rate over an experimental period of 332 days. The total liveweight gain of autumn-implanted cattle did not differ significantly from that of spring-implanted animals. Response to autumn-implantation appeared expended after 149 days, but there was a suggestion that the effectiveness of spring treatment was still present at slaughter, after 183 days. Over-all growth rate in spring-summer was notably superior to that in autumn-winter. Chilled carcass weight was significantly increased under hormone treatment, with no significant difference between autumn- and springimplantation. Dressing-out percentage appeared unaffected by hormone treatment, although a sl'ightly increased fasting loss was recorded for treated steers. Prediction equations were presented to permit accurate estimation of starved liveweight from weights recorded after variable times of fasting.