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Effects of Stilbestrol in Altering Carcass Composition and Feed Lot Performance of Beef Steers^{1, 2, 3,}

University of Wisconsin⁴, Madison

Abstract

The effects of orally administered stilbestrol were studied in two trials involving a total of 80 yearling steers. Three levels of stilbestrol were fed: 0 mg., 10 mg., and 30 mg. per steer per day. Protein, moisture, and fat content of the carcass, certain slaughter and carcass characteristics, and feed lot performance were studied at 0, 56, 112, and 168 days during a 168-day fattening period.

The 10-mg. level of stilbestrol did not significantly stimulate rate of gain above that of the controls, nor was there a marked increase in feed efficiency during any of the three stages. Steers fed at the 30-mg. level of stilbestrol gained 0.32 lb. (P<0.01) and 0.34 lb. (P<0.05) more than the controls for the 0–56 and 0–112 day stages and 0.32 lb. (not significant) more during the 0–168 day stage.Feed efficiency was increased up to 12% during the 0–112 day stage. Both levels of stilbestrol increased efficiency of protein conversion from feed to carcass. On an energy conversion basis there was little or no difference between efficiency of control and treated steers when stilbestrol was fed for at least 112 days.

Stilbestrol caused an increase in carcass protein and moisture and a decrease in carcass fat as compared to untreated controls. These effects were more pronounced at 56 days than at 112 or 168 days. The most significant alteration in carcass composition was obtained with the 30-mg. level of stilbestrol. Treatment did not significantly affect live or carcass grade, nor percent bone in the carcass. Carcass conformation was only slightly altered, those wholesale cuts affected somewhat by treatment being the rump, foreshank, brisket, and kidney knob.

Results indicate that stilbestrol stimulates the growth phase of steers and causes increased protein deposition early in the feeding period. This effect becomes less with prolonged supplementation. Thus, the age of the steers and/or the length of time on feed are factors which strongly influence the extent to which stilbestrol treatment will alter carcass composition or quality.

¹ Published with the approval of the Director of the Wisconsin Agricultural Experiment Station, Madison.

² The authors wish to express their appreciation to Dr. P. H. Phillips for his assistance and advice during the course of the experiment.

³ Acknowledgement is made to Chas. Pfizer and Co., Terre Haute, Ind. and to Eli Lilly Co., Indianapolis 6, Ind.for contributing the stilbestrol used in this experiment.

⁴ Departments of Animal Husbandry and Biochemistry, Madison.