Effect of short- and long-acting growth promotants on grazing beef cattle in south-west Queensland.

Abstract

The effects of a single implantation of a short-acting (< 120 days) growth promotant - 36 mg zeranol (Ralgro) - were studied with one, two and three year old steers grazing Mitchell (Astrebla spp.) grasslands from March to June 1981 (107 days) in south-west Queensland. Implantation increased (P<0.05) mean final liveweight by 9.7, 18.1 and 11.0 kg for the one, two and three year old steers, respectively (control groups 317.6 kg, 432.3 kg and 519.1 kg). Tn a second experiment, the effects of a single implantation of a long-acting (400 days) growth promotant - 45 mg oestradiol 17 beta (Compudose 400) - were studied with steers grazing Channel pastures from October 1983 to April 1985 (540 days) in far south-west Queensland. Implantation increased (P<0.01) both mean final liveweight by 30.7 kg (control group 577.1 kg) and carcass weight by 14.2 kg (control 306.4 kg). Daily liveweight gains for implanted and control steers were 0.48 kg and 0.43 kg per day respectively @<0.01). There was no significant difference between the implanted and control steers in dressing percentage (52.7 cf. 53.2%) and fat ;hicknes.s at the P8 rump sGe (20.2 cf. 18.9 mm).