Some effects of implanted hexoestrol on the growth of steers

Abstract

1. An experimental test of the effects of 15, 30 and 60 mg. of hexoestrol (ear implants) on growth (over a period of 95 to 98 days) has been carried out in Argentina, using 172 Hereford steers (all 4–5 years old).2. On pasture where the growth rate was only about 0·4 kg. a day, the optimum dose was 30 mg., which gave an extra 0·14 kg. per day.3. The carcasses from the 30 mg. group were significantly heavier by 8 kg., those from the 15 mg. group by 7 kg., but those from the 60 mg. group were only 3 kg. heavier than those from the control group.4. It is suggested that both the poorer response and the lower optimum dose were due to the poorer pastures on which this experiment was carried out.5. Evidence for the carcasses of the treated animals being significantly leaner than the controls was given by the 60 nag. group—the grading was poorer, the excess kidney fat was less, and the subcutaneous fat was thinner.6. Carcass measurements showed differences in the treated groups, but these in general followed the differences in carcass weight.7. Measurements of width of thigh and thorax provided evidence that the depth of carcass had been increased by hexoestrol.8. The incidence of ‘tail raising’ had been increased from 10% in the control group, to 50% and more in the 15, 30 and 60 mg. groups. Carcasses from such animals had a slightly greater width at the thigh.9. The existence of an optimum dose is not thought to be due to restlessness, as indicated by ‘tail raising’, but to a depressant action of hexoestrol on growth. In this connexion, data on the weights of the kidneys show that the 60 mg. dose decreases kidney weight (and implicitly the level of protein metabolism) to the value of the control.10. Evidence was obtained of a rapid change in live weight when the steers were without food. During a single morning this was, on the average, about 13 kg. per animal, followed by a further 25 kg. during the subsequent 24 hr. (see Appendix II).