Relationship of Testicular Weight to Age and Scrotal Circumference of Holstein Bulls

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Abstract
Testicular weights were recorded for 250 Holstein bulls ranging in age from 19-189 mo. The multiple regression equation that best described the relationship between paired-testes weight and age of bull was .cxa.Y = -368.8 + 952.2 log X - 180.3 (log X)2, where .cxa.Y is paired-testes weight in g and X is bull age in mo. Correlations between these 2 variables were .86 for 24 bulls .ltoreq. 60 mo. of age and .60 for 23 > 60 mo. of age. A linear regression equation for 47 bulls was .cxa.Y = -645.5 + 34.0 X, where .cxa.Y is paired-testes weight in g and X is scrotal circumference in cm measured within 1 mo. of slaughter. The correlation coefficient was .79. Differences in testicular weights of bulls of similar ages were large. These should be taken into account by measuring scrotal circumference and selecting young bulls with larger testes and superior spermatozoal producing capabilities.