Testosterone and Libido in Holstein Bulls of Various Ages

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Abstract
Testosterone was measured by radioimmunoassay in the blood plasma collected from 197 and 195 Holstein bulls in the spring and fall seasons, respectively. Bulls ranged in age from 8 mo.-13.5 yr. The average value for spring was 8.0 ng/ml, higher than the value of 5.7 ng/ml in the fall. There was a tendency for testosterone to increase with age of the bulls up to 6-7 yr. The concentration of circulating testosterone was unrelated to libido or semen quality.