Relationships between Blood Plasma Testosterone, Weaning Treatment, Daily Gains and Certain Physical Traits of Young Angus Bulls

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Abstract
Testosterone in blood plasma averaged .09 ± 1 ng/ml in 51 yearling steers and 7.0 ± .1 ;/ml in 72 Angus bulls sampled at 263 ± 1.7, 12 ± 1.7 and 375 ± 1.7 days of age. Bulls were eaned either at 120 days (n = 38) or 207 days i = 34) of age. After 207 ± 1.7 days of age hey were fed rations differing only in dietary irotein (8, 10 and 14% protein) for intervals of 56 days or less and of 12% protein up to 168 days. Dietary protein had no significant effect on testosterone (ng/ml plasma), scrotal circumference or sperm concentration and motility. Age at weaning was unrelated to subsequent daily gains or to body weight at 375 days, but bulls weaned at 120 days averaged higher (P<.01) in testosterone than bulls weaned at 207 days (7.8 ± .5 vs 6.1 ± .4 ng/ml plasma). Concentrations of testosterone (5.9 ± .5 to 8.9 ± .6 ng/ml) in plasma were related positively to daily gain, were about 2 ng/ml higher in bulls scoring above average in masculinity (both P<.01), and not significant for other variables (linear-quadratic functions of age, weaning weight, body weight, scrotal circumference, sperm concentration and motility, and linear functions of scores at 375 days for fatness, body frame, muscling, and length and texture of hair). Scrotal circumference at 375 days of age was greater (P<.01) in bulls weaned at 120 days than those weaned at 207 days and was correlated (P<.01) positively with sperm concentration and with sperm motility. Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.

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