Comparative studies on bull and stallion seminal DNase activity and interaction with semen extender and spermatozoa

We performed a series of comparative studies of bull and stallion seminal plasma (SP) and its role on sperm-neutrophil binding as well as the interaction between semen extender and seminal DNase. Because of contrasting roles of SP on sperm-neutrophil binding between horses and cattle, it was suspected there were some species-specific differences on sperm interaction with SP proteins due to the variations in the natural location of semen deposition (uterus compared to vagina). Bull frozen-thawed sperm removed from egg yolk extender showed similar results to fresh sperm, but this also caused extensive sperm agglutination unless SP or egg yolk was included. If similar agglutination occurs after AI with frozen bull semen, it could interfere with sperm transport or sperm functions. Commonly used bull semen extenders were poor media for seminal DNase activity on plasmid DNA degradation, raising the prospect that the same may be true with other SP factors important to fertility. DNase activity per mg SP protein of bulls was less than that of horses (P<0.05), but DNase activity associated with bull sperm was greater (P<0.05) indicating a different affinity of DNase to spermatozoa. This could be related to the fact that bull sperm naturally migrate from the vagina to the uterus leaving the bulk of SP behind. In such migration, sperm cells needed to carry DNase and other SP factors along. Incorporation of egg yolk in bull semen and introducing SP into the uterus of cattle with current AI protocols may contribute to reduced fertility. Modifications of semen extender and/or semen processing should be examined to allow sperm cells a maximum potential for fertilization.