Sexual and aggressive behaviors of Hereford bulls: interrelationship of variables and problems with the use of composite scores to describe overall sexual performance

The purpose of this investigation was to determine the interrelationships of the various sexual and aggressive behaviors exhibited by Hereford bulls in sexual performance (serving capacity) tests and to determine the extent to which these interrelationships change with age (maturity). Correlation matrices were constructed for the frequencies of sexual and aggressive behaviors exhibited by two groups of 13 and 14 bulls, respectively, during 120-min tests with females when the bulls were 12, 18, and 24 mo of age. The frequencies of selected sexual behaviors recorded during individual tests at 18, 21, and 24 mo were factor-analyzed using a principle components analysis. Also, a comparison was made of the length of the refractory periods following various sexual behaviors at 12 and 24 mo of age. Bulls varied greatly in the way they responded to sexual stimuli. Few sexual behaviors were intercorrelated and the factor analysis of selected sexual behaviors was inconclusive. Frequencies of aggressive behaviors were more highly correlated. Age (maturation) did not affect the interrelationship of the sexual behaviors recorded. Aggressive behavior variables were more highly correlated at 12 mo than at 18 or 24 mo of age. The average length of the refractory period following ejaculation was longer (112 s; P .05) than the refractory period following mounts without ejaculation (50 s), and the latter had a longer (P .05) refractory period than mount attempts, mount intentions and head throws (26 to 38 s). In conclusion, the relatively poor interrelationships among sexual behaviors in bulls will hamper efforts to objectively compare the sexual performance of different bulls using rating systems based on a composite index of sexual responses