Development of penis and sheath in young dairy bulls, and its relationship to age and body weight

Abstract

1. Eighty-six bull calves (fifty-two Friesian, twenty-two Ayrshire, twelve Shorthorn) were examined at intervals, during the first year of life, by a method which allowed classification of the degree of adherence between penis and sheath into five classes.2. Mean age and weight at which separation between penis and sheath commenced and was completed are recorded for each breed. Significant breed differences were found.3. The rate of separation accelerates as development proceeds.4. The relationships between age, body weight, and commencement and completion of separation in the Friesian bulls are analysed by correlation methods. These analyses suggest that both age and body weight are important in sexual development.5. An equation is given for the linear regression of age at completion of separation on age and weight at commencement of separation and weight at 10 weeks for the Friesian bulls.