The relationships between reproductive performance traits of beef bulls in natural mating systems and subjective and objective parameters of sperm and related structures

Twelve Angus and 7 Polled Hereford bulls were used to determine the relationship of various semen quality attributes to various measures of reproductive efficiency. The semen quality characteristics evaluated were: volume, concen-tration, motility, vigor, percent live, percent live normal, percent live immature, percent live normal, percent dead, percent dead normal, percent dead immature, percent dead abnormal and percent intact acrosomes. Scrotal circumference measurements were also taken. Correlations between the semen quality characteristics indicated highly significant relationships between concentration, motility, vigor and percent live and percent dead cells. Sperm morphology classifications were also highly interrelated. Scrotal circumference was not consistently related to any of the ejaculate characteristics. Reproductive performance was evaluated using 3 different expres-sions: the number of estrous cycles the females completed while in the presence of the bull, the mean calving interval for parous, lactating females assigned to each bull and the conception rate for each bull. All calculations were made in an attempt to avoid penalizing the bull for the parity status of the females. Although these traits were highly correlated among themselves, few significant correlations existed with the semen quality characteris-tics. The results of this study indicate the need for an extended study with larger numbers of observations, in order to accomplish more than just defining bulls with increased or impaired fertility.