Studies on the Use of Hormones in Lamb Feeding

In a series of three feeding trials with 432 lambs several estrogenically active compounds were studied to determine their value for the production of market lambs. In Trial I lambs which received 100 mg. progesterone—10 mg. estradiol implants or were fed 5 mg. of stilbestrol reduced to 2.5 mg. by the end of the feeding period gained significantly faster than control lambs. In a second trial lambs fed stilbestrol either continuously or for the first half of the feeding period (levels of 5 mg. per lamb later reduced to 1 mg. or zero) gained slightly faster than controls. Benzestrol-fed lambs also showed some increase in rate of gain, but none of these increases was significant. A third trial in which stilbestrol (5 mg. per lamb later reduced to 2.5 mg.) was fed either alone or in combination with thyroprotein (0.75 gm. per lamb daily) or thiouracil (0.50 gm. per lamb daily for the last half of the trial) again demonstrated significantly faster gains for both stilbestrol and stilbestrol-thyroprotein supplemented lots. Thiouracil addition decreased the rate of gain below that of these two groups as did benzestrol. Estrogenic hormone use in all trials increased feed efficiency and the faster gaining lambs tended to make the most economical gains. In comparison of concentrate treatments containing either shelled yellow corn or cooked red kidney beans, the latter gave faster gains in all trials and the difference was significant in the third trial. The feeding of uncooked beans to a group on Trial III resulted in a reduced feed intake and significantly slower gains. The faster gains resulting from feeding the cooked kidney beans were not accompanied by an increased efficiency of gain. All supplements used except benzestrol consistently produced lambs that graded lower, both alive and in the carcass, than did control lambs. They increased the moisture content of the edible tissue of the carcasses and also increased the protein and ash but lowered the fat content of the dry matter. The supplements which caused the greatest alteration in carcass composition were those that promoted the fastest growth rate, stilbestrol in all trials and the stilbestrol-thyroprotein combination in Trial III.