In vitro capacitation of ejaculated rabbit spermatozoa

Prior to fertilization mammalian spermatozoa undergo physiological changes in the female reproductive tract. These changes are collectively known as capacitation. In essence capacitation is a further differentiation that the sperm cell must acquire beyond the maturational changes that it undergoes in the epididymis. Although capacitation in vitro has been easily achieved in rodents, its accomplishment in the rabbit is inconsistent and difficult. We report here successful in vitro capacitation of ejaculated rabbit sperm, assessed by in vitro and in vivo fertilization of rabbit ova. Sperm were used from pooled ejaculates collected from bucks of proven fertility since sperm collected from individual bucks resulted in significant differences in fertilization levels. Conditions favoring in vitro capacitation were: (1) extended incubation time of 12 h, (2) addition of 20% heated rabbit serum to incubation medium, and (3) an atmosphere of 5% CO2, 8% O2, and 87% N2 during incubation. In vitro capacitation of sperm under these conditions resulted in 67% fertilization compared to 89% for control sperm capacitated for 13 h in the uterus.