Effects of long acting and short acting oestradiol implants on growth rate and carcase weight of steers.

The effects of a number of steroid hormone treatments on growth were examined in a trial involving 204 Friesian-type steers which was carried out over an 11 month period from May to April. The animals were at pasture from May until October and were over-wintered indoors on grass silage and supplementary concentrates. Thirty-four animals were used as untreated controls, and there were four treatment groups: 43 steers were implanted with pellet-type implants containing 20 mg oestradiol benzoate and 200 mg progesterone on days 1, 105 and 187; 47 steers were implanted with a single silastic rubber implant containing 45 mg oestradiol-17 beta; 36 steers received treatment (1) and in addition were implanted on the same days with 300 mg trenbolone acetate; 44 steers received treatment (2) and were also implanted with 300 mg trenbolone acetate on days 1, 105 and 187. The mean liveweight gains (+/- sem) of the steers during the first 249 days of the trial were 201.7 kg for the controls and 236.8, 219.4, 254.4 and 247.8 (+/- 6.1) kg for the steers assigned to treatments 1, 2, 3 and 4, respectively. The corresponding values for the carcase weights (+/- sem) were 300.0 kg for the controls and 318.4, 312.0, 327.9 and 321.6 (+/- 3.5) kg for the treated groups. Although all the treatments increased the liveweight gains and carcase weights significantly compared with the controls, the responses to the silastic rubber implants were smaller owing primarily to an apparently high rate of loss of the implants.(ABSTRACT TRUNCATED AT 250 WORDS)