Sperm-bound antisperm antibodies prevent capacitation of bovine spermatozoa.

It was hypothesized here that sperm-bound antisperm antibodies (ASAs) impair the ability of bovine spermatozoa to undergo capacitation, bind to the zona pellucida, and complete the acrosome reaction. The effect of ASA binding on these functions was evaluated in frozen/thawed spermatozoa from four bulls before and after induction of ASAs. Ejaculates were divided into ASA negative (<10% immunoglobulin [Ig]G- and IgA-bound spermatozoa) or ASA positive (≥20% IgG and/or IgA-bound spermatozoa). The percentage of capacitated (Merocyanine 540 positive) live spermatozoa in response to heparin was lower in ASA-positive than ASA-negative ejaculates (P < 0.0001). Treatment with heparin resulted in a higher percentage of capacitated spermatozoa compared with control treatments in ASA-negative but not ASA-positive ejaculates. The percentage of capacitated spermatozoa after heparin treatment was negatively correlated with IgA (P = 0.02, R2 = -0.48) but not IgG binding. Sperm binding to the zona pellucida was lower in IgA-positive (six spermatozoa/oocyte; 3-10 spermatozoa/oocyte) than IgA-negative ejaculates (seven spermatozoa/oocyte; 4-13 spermatozoa/oocyte) (P = 0.019). Zona binding was negatively correlated with the percentage of IgA-bound spermatozoa (P = 0.04; R2 = -0.24) but not IgG-bound spermatozoa. The percentage of acrosome-reacted spermatozoa was higher in calcium ionophore A23187-treated than control aliquots in both ASA-negative and ASA-positive ejaculates (P < 0.0001). However, the percentage of acrosome-reacted spermatozoa did not differ between ASA-positive and ASA-negative samples, and no correlation was identified with IgG or IgA binding. It was concluded that sperm-bound IgA affected the ability of bovine spermatozoa to undergo capacitation. ASAs inhibited the changes in plasma membrane fluidity associated with capacitation and binding of spermatozoa to the zona pellucida.

Pregnancy outcomes using stallion epididymal sperm stored at 5 °C for 24 or 48 hours before harvest.

The cryopreservation of epididymal sperm can be useful in a variety of circumstances for ensuring genetic preservation of a valued stallion. Although early studies have reported pregnancy rates significantly lower than those achieved with cryopreserved ejaculated sperm, two recent studies report over 60% one-cycle pregnancy rates with epididymal sperm stored for 24 hours at 5 °C before harvest and cryopreservation. The aims of this study were to: (1) attempt to replicate the one-cycle pregnancy rate of over 60% using epididymal sperm cooled and stored within the epididymis for 24 hours before harvest and cryopreservation and (2) evaluate pregnancy outcome with sperm cooled and stored within the epididymis for 48 hours before sperm harvest and cryopreservation. Testicles were obtained from 13 stallions undergoing routine castration. The epididymides were stored at 5 °C for either 24 or 48 hours before sperm harvest and cryopreservation in an egg yolk and dimethylformamide-based freezing extender. Thirteen mares were bred on one cycle with cryopreserved epididymal sperm stored for 24 hours before harvest, and 10 of those 13 mares were also bred on a previous or subsequent cycle with samples from the same stallion that had been stored for 48 hours before harvest. Pregnancy occurred in 7 of the 13 inseminations of sperm stored for 24 hours before harvest, and in 4 of the 10 inseminations of sperm stored for 48 hours before harvest. The pregnancy rate using epididymal sperm stored for 24 hours before harvest is consistent with that of previous reports. In addition, these results provide evidence that pregnancies can be achieved when the epididymides are cooled and stored for 48 hours before sperm harvest and cryopreservation.