The use of the hormones, diethylstilboestrol, hexoestrol and testosterone propionate, as growth stimulants in beef cattle has been studied.

The subcutaneous implantation of 60 mg. stilboestrol into steers fattening in yards produced a highly significant increase in rate of gain (65%) and little difference in the yield and quality of the carcass. The implantation of 24 nig. or 36 mg. of diethylstilboestrol or 30 mg. hexoestrol into Friesian bullocks fattening on pasture produced highly significant increases in rates of gain (29%, 48% and 33% respectively). No significant difference was found in the rates of gain produced by these three treatments.

The oral administration of 10 mg. diethylstilboestrol per head per day for 168 days or the oral administration of 20 mg. rising to 40 mg. testosterone propionate per head per day for 154 days to dizygotic twin steers on equal feed intake significantly increased rate of gain by 15% and 21% respectively Feed efficiency as measured by the pounds of feed required to produce a pound of gain was significantly improved by both treatments. Carcass yield and carcass quality were not significantly affected by either treatment. No significant differences were found between the two treatments.

Examination of the thyroid and adrenal glands of treated and untreated steers revealed no consistent changes in size due to treatment. The gonadotrophin and thyrotrophin content of the anterior pituitary glands of treated and untreated cattle were compared using the male chick bioassay. The results showed that a lower gonadotrophin content was not a factor associated with the extra growth due to treatment, but in two out of three experiments there was some evidence that sex-hormone treatment leads to a mild hyper-thyroidism which, in turn, resulted in a decrease in the thyrotrophin content of the anterior pituitary gland. It was concluded that hyperactivity of the thyroid gland was probably more important in accounting for the extra growth than hyperactivity of the adrenal cortex.

Data from Danish Progeny Testing Stations were used to investigate the relationship between the colour of meat and feed efficiency in pigs. For groups slaughtered during the summer there was a highly significant correlation. As the amount of feed consumed per unit live-weight gain declined so the meat became paler. For groups slaughtered in winter and for data pooled over the whole year, there was no significant correlation. Possible explanations of these findings are discussed.