Effect of accessory sex gland fluid from bulls of differing fertilities on the ability of cauda epididymal sperm to penetrate zona-free bovine oocytes

Abstract

The ability of accessory sex gland fluid to affect the fertility of cauda epididymal sperm was evaluated for 10 bulls that ranged in fertility from 6.2% below to 6.0% above the average fertility of bulls at artificial breeding cooperatives. Cauda epididymal sperm collected from indwelling vasa deferentia catheters and cauda epididymal sperm exposed to accessory sex gland fluid from the same bull were compared on the basis of their rates of in vitro penetration of zona-free oocytes after heterospermic insemination. Incubation of cauda epididymal sperm with accessory sex gland fluid significantly enhanced the ability to penetrate oocytes, and bull fertility affected the magnitude of this improvement. For bulls of average and higher fertility, the positive influence of accessory sex gland fluid on penetrating ability of sperm was highly significant (p < 0.0001). Accessory sex gland fluid from bulls of below average fertility also improved the penetrating ability of cauda epididymal sperm, although not significantly (p = 0.07). Heterospermic competitions compared the penetrating ability of cauda epididymal sperm exposed to homologous accessory sex gland fluid with a portion of the same sperm population incubated in heterologous accessory sex gland fluid from a bull of contrasting fertility. In experiments involving sperm from 12 different bulls, paired in 42 fertile/subfertile combinations, samples of cauda epididymal sperm mixed with accessory sex gland fluid from the higher-fertility bulls had greater oocyte-penetrating ability than when aliquots of that sample were mixed with accessory gland fluid from lower- fertility bulls (p < 0.0001). We concluded that accessory sex gland fluid augments the fertility of cauda epididymal bull sperm, and that the magnitude of this effect is influenced by the fertility of the bull providing the accessory sex gland fluid