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Growth and Fattening Stimulation in Ewe Lambs by Certain Androgenic and Estrogenic Compounds¹

Iowa Agricultural Experiment Station, Ames

Abstract

Results from three individual and two group-feeding experiments involving 324 Western ewe lambs are reported.

An injection of 3.3 mg. of testosterone propionate per 100 lb. live weight per day increased rate of gain in ewe lambs by 38% (significant at P=.O5) and increased feed intake over control lambs in one experiment, but neither this injected dose nor a 30 mg. pellet implant had any effect on gains in three subsequent trials. Methyl testosterone, fed at levels of either 8.4 or 42.9 mg. per lamb daily, produced a significant increase in rate of gain in Experiment 1, but the higher level was without effect on gains in subsequent trials. Carcass grades were highest in the group fed the higher level of methyl testosterone and lowest in the group injected with testosterone propionate in the trial in which these androgens significantly increased rates of gain. When effective in stimulating gains, testosterone propionate increased the size of the thyroids. Shorn lambs implanted with 30 mg. of testosterone propionate gained 27% faster than their wooled pen mates, but failed to gain significantly faster than either shorn or wooled control lambs.

An implant of 250 mg. of progesterone plus 10 mg. of estradiol increased rate of gain significantly, improved feed efficiency, and increased the daily consumption of corn, but not of total feed. This treatment lowered carcass grades significantly and 50% of the carcasses were classed as yearlings. Excessive riding was evident by the fourth day after implantation and 20% of the lambs accepted a, vasectomized ram at least once during the first half of a 71-day trial.

The feeding of 3.5 mg. of stilbestrol per ewe lamb daily produced significantly greater gains (Experiment 5), but this level could not be tolerated by similar ewe lambs in Experiment 4. Feeding 2 mg. of stilbestrol per lamb daily had no effect (Experiment 3), reduced gains significantly (Experiment 4) and increased gains by an amount just short of significance in Experiment 5. Actual carcass grades (lamb basis) were lowered, but not significantly, by either 2 or 3.5 mg. of stilbestrol per lamb per day and the percentage of yearling carcasses increased with the level of stilbestrol fed.

The progesterone-estradiol implant increased uterine size significantly and reduced the size and number of follicles, but had no effect on the weight of the ovaries. Stilbestrol increased uterine size, decreased ovary size and retarded follicle development; whereas testosterone propionate had no significant effect on any of these measurements, but tended to increase ovary weights and number of developing follicles.

¹ The authors express acknowledgment to Ciba Pharmaceutical Products, Inc. for the methyl testosterone and testosterone propionate used.

² Journal paper No. J-3060 of the Iowa Agricultural Experiment Station, Ames, Project No. 869.