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The Effect of Steroid Hormones on Fattening Lambs¹

Michigan State University

Abstract

Three experiments were conducted with fattening lambs to determine the effect of various steroid hormones and combinations of hormones on feedlot performance and carcass quality.

Lambs implanted with a combination of 250 mg. progesterone and 10 mg. estradiol exhibit more rapid, economical gains and a larger daily feed intake than control lambs. When all lambs are slaughtered after the same length of time on feed, there is no significant difference in carcass grade between controls and progesterone-estradiol implants. However, when lambs are topped out of the feedlot at various intervals, the progesterone-estradiol implanted lambs have a lower dressing percent and carcass grade than lambs without hormone treatment. The progesterone-estradiol implant tended to produce fat with a higher moisture content.

A combination implant of 100 mg. progesterone and 10 mg. estradiol compared favorably with the 250 mg. progesterone-10 mg. estradiol implant but one lamb was afflicted with urinary calculi.

A combination implant of 50 mg. testosterone and 10 mg. estradiol produced similar results as progesterone-estradiol with the exception of more restlessness in the feedlot.

The feeding of 3 mg. stilbestrol daily produced no significant improvement over the progesterone-estradiol implants, although the lambs tended toward an improved dressing percent with a slower daily gain and higher feed requirement.

Hormone treated wether lambs exhibit hypertrophy of the secondary sex organs and both wethers and ewes exhibit mammary development. Difficulty in pelting and obtaining the break joint was experienced at slaughter. The absorption of progesterone is low in comparison to other hormones and is affected by the site of implantation; the ear being less efficient than the sub-maxillary region. The ear was a satisfactory implantation site for hormones other than progesterone.

Implants of 250 mg. progesterone; 100 mg. delta 4 androstene 3, 17 dione; 10 mg. estradiol; or 60 mg. testosterone produced no advantages over control lambs.

¹ Published with the approval of the Director of the Michigan Agricultural Experiment Station as Journal Article No. 1962.

² Departments of Animal Husbandry and Physiology and Pharmacology, East Lansing.

³ This work was supported by grants from Chemical Specialties Co., Inc., New York, New York.