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Comparison of Four Levels of Protein Supplementation with and without Oral Des on Reproductive Traits and Testosterone of Bulls^1,2,

Purdue University, West Lafayette, IN 47907

Abstract

Diethylstilbestrol (DES) at 0 and 10 mg daily and four levels of protein supplementation (.23, .41, .59 and .77 kg/day of 50% protein soybean meal) were the variables in a 2 x 4 factorial arrangement of treatments. Over 2 years, 153 Angus bulls were assigned to the study. Plasma testosterone was measured at the end of the 140-day feeding period (average of two samples) and in a post-trial period (one sample). Post-trial measurement was 35 days after withdrawal of DES and equalization of protein supplementation (.45 kg/day) for all bulls. Observations of masculinity score, scrotal circumference, testicular consistency, sperm motility, sperm concentration and percentage normal sperm were made during a 2-week period following the 140-day feeding trial. Over the 2 years, bulls on 10 mg DES daily averaged 12.8 ng/ml testosterone while control bulls averaged 9.3 ng/ml at 140 days on feed, and this difference was significant (P<.01) in both years and in the pooled analysis. Level of protein supplementation affected 140-day testosterone in the first year (higher plasma testosterone on higher protein supplementation) but not in the second year. This resulted in a significant (P<.05) average main effect of protein and a highly significant (P<.01) interaction of years with protein treatments. Post-trial testosterone in plasma was unaffected by either DES or level of protein supplementation. Neither protein nor DES treatment produced significant effects on masculinity score, scrotal circumference, testicular consistency or semen traits.

Plasma testosterone was positively (r = .23; P<.05) correlated with daily gain. Body weights were positively correlated with masculinity score (r = .39 to .47; P<.01), scrotal circumference (r = .48 to .52; P<.01) and sperm motility (r = .29 to .31; P <.01). Plasma testosterone was not significantly associated with masculinity score or any of the reproductive traits.

¹ Journal Paper No. 7216, Purdue University Agricultural Experiment Station. A contribution from the Department of Animal Sciences.

² Data derived from the Purdue University contributing project to NC-1 regional project entitled Improvement of Beef Cattle Through Breeding Methods.

³ Present address: R. R. No. 4, Box 48, Franklin, IN 46131.