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Comparison of Four Levels of Protein Supplementation with and without Oral Diethylstilbestrol on Blood Plasma Concentrations of Testosterone, Growth Hormone and Insulin in Young Bulls¹

Purdue University, West Lafayette, IN 47907 and and Lilly Research Laboratories, Greenfield, IN 46140

Abstract

Angus bulls (77 head) were assigned to four levels of supplemental protein (.23, .41, .59 and .77 kg/day soybean meal) with and without oral diethylstilbestrol (DES; 10 mg/day). Daily gains were calculated over the 140-day feeding trial and during a 28-day post-trial period in which supplemental protein was equalized at .45 kg/day for all bulls and DES was withdrawn. Blood was drawn for assay of plasma concentrations of testosterone, growth hormone (GH) and insulin at 0, 28, 92 and 140 days on trial, and in the post-trial period. Testosterone concentrations in blood from DES and control bulls were, respectively, 9.4 and 13.1 ng/ml at 28 days on feed (P<.01) but at 140 days the effect was reversed (12.5 and 8.6 ng/ml) and significant (P<.01). DES treatment produced no significant effects on plasma insulin and effects on plasma GH were highly variable. Higher plasma insulin was noted in bulls receiving higher protein supplementation at 28, 92 and 140 days, but this effect disappeared in the post-trial period after equalization of protein supplementation. Elevated plasma testosterone was observed on day 28 in bulls receiving more protein, but there was no effect of protein levels on days 92 and 140 and in the post-trial period. Highest levels of plasma GH were observed in bulls on the lowest (.23 kg/day) level of protein supplementation. Insulin values were significantly repeatable from one sampling date to another while testosterone and GH, known to be released episodically, had repeatability values near zero. Correlations among the hormones were very low (.06 for testosterone with GH, .12 for testosterone with insulin and –.06 for GH with insulin). A linear function of insulin (r = .38, P<.01) was the best predictor of average daily gain.

¹ Journal Paper No. 7293, Purdue Univ. Agri. Exp. Sta. A contribution from the Dept. of Animal Sciences.

² Dept. of Animal Sciences, Purdue Univ.

³ Lilly Research Laboratories.