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Relationship of Body Weight to Testicular Sixe and Consistency in Growing Holstein Bulls¹

Cornell University³, Ithaca, NY 14853

Abstract

The relationship between 1,203 measurements of scrotal circumference and testicular consistency, usually made at 6-month intervals, and body weight in 411 Holstein bulls, primarily 6 to 72 months of age, were analyzed. All bulls were weighed within 14 days of testicular measurement. The relationship between body weight in kg () and bull age in months (X) is described by the regression equation, = –65.18 + 42.14 X –.39 X₂, (r = .96). The equation that describes the relationship between body weight in kg (X) and scrotal circumference in cm () is, = 22.5 3 + .032 X –.000013 X₂, (r = .81). The linear regression equation relating average testicular tonometer deflections in mm () and bull weight in kilogram (X) is = 15.35 –.0028 X, (r = –.45). When age was held constant the partial correlation between scrotal circumference and body weight was .58 (P<.01). Thus, as expected, body and testis size were correlated, but reports of similar relationships often have ignored the common and considerable influence of age. There was no uniform relationship between body weight and testicular consistency, although the partial correlation of –.16 (P<.01) indicates that heavier bulls, and perhaps those which were fatter, tended to have softer testes. Bulls with large testes may be larger, partly because of an anabolic effect of androgens, but this is speculative because these data do not permit distinction between a causal and casual relationship.

¹ The authors appreciate the help of P. D. Miller and American Breeders Service in making body weight data available and J. Schiavo in processing the data. Helpful comments were made on the manuscript by P. D. Miller.

² Address: Dr. G. H. Coulter, Agriculture Canada Research Station, Lethbridge, Alberta, Canada T1J 4B1.

³ Department of Animal Science.