The influence on growth rate and slaughter characteristics of implanting fattening male hoggets with various levels of hexoestrol and diethylstilboestrol

Abstract

In three trials involving 288 hoggets the influence on growth rate of implanting 15 mg. hexoestrol or 12 mg. stilboestrol was compared. In one trial the influence of adding excipient to either stilboestrol or hexoestrol to increase the surface area of the implant was also assessed. Live-weight gain was calculated for each time interval after implantation and it was concluded that after approximately 140 days the influence of implantation had largely disappeared. For optimum benefit to live-weight gain implantations should be made approximately 100 days prior to slaughter.In all trials, implantation with synthetic oestrogens resulted in extra daily live-weight gain, the increase for all animals amounting to 31% extra daily gain for hexoestrol and 26% for stilboestrol. The addition of excipient to the implant diminished the initial growth response and reduced the extra gain achieved.Implantation with the synthetic oestrogens significantly increased the final live-weight on the farm, live-weight before slaughter and carcass weights when groups of animals from each treatment were slaughtered together.Stilboestrol and hexoestrol implantation resulted in an extra 4·7 and 6·1 lb. full live-weight; 3·7 and 5·3 lb. empty live-weight and 1·3 and 2·8 lb. extra carcass weight respectively, compared to controls killed at the same time.Where hoggets had received a high-plane diet, treatment did not affect killing-out percentage, but where the level of nutrition was lower a decrease of up to 1% was observed. In all trials treatment with the synthetic oestrogens resulted in an increase in pelt weight and in one trial this increase was up to 2 lb.Implantation with hexoestrol and stilboestrol increased the size of the gut full and empty in two of the trials. The differences were reduced when the gut weights were corrected to 100 lb. empty live-weight. The weight of the thyroid gland or the total weight of the trachea, heart and lungs were not affected by treatment.The approximate rate of uptake of hormone from a 12 mg. implant of stilboestrol was assessed by the decrease in the weight of dried tablet removed at slaughter from 30 to 200 days after implantation. The linear regression y (uptake in mg.)=3·029+0·039x (days from implantation) fitted the data best, giving an approximate average uptake over this period of 39 micrograms of stilboestrol per day.