Cooling rates,storage temperatures and fertility of extended equine spermatozoa

Two experiments were designed to evaluate cooling rates and storage temperatures for stallion spermatozoa extended in caprogen (CAP), Cornell University extender (CUE), heated skimmilk (SM) and a nonfat-dried milk solids glucose extender (NFDMS-glucose). In Experiment 1, each extender was evaluated in a separate but similar 4 × 4 × 6 factorial trial using two ejaculates from each of six stallions. Aliquots of 66 × 10⁶ spermatozoa were transferred to each of 16 coded tubes and extended to 6 ml with SM, CAP, CUE or NFDMS-glucose. Four tubes of extended semen were either plunged into 5C water or cooled at a rate of ?1.0, ?0.5, or ?0.2C/min. Within each treatment, one tube of extended semen was maintained at 20C, 15C, 10C or 5C. Progressive spermatozoal motility was estimated immediately after dilution (0 h) and at 4, 8, 12, 24 and 36 h. Regardless of extender, all three slower cooling rates were superior (P<0.05) to plunging to 5C; storage temperatures of 20C and 15C were superior (P<0.05) for maintaining spermatozoal motility. Experiment 2 was designed so that all extenders could be evaluated simultaneously. Since CUE resulted in an immediate depression of spermatozoal motility, it was not evaluated further. Semen was collected from 12 stallions and each ejaculate was extended in SM, CAP and NFDMS-glucose. Semen was cooled at ?1.0C/min and maintained at either 20C or 15C. Spermatozoal motility was assessed as in Experiment 1. Overall, the CAP and NFDMS-glucose extenders were superior (P<0.05) to SM for maintenance of spermatozoal motility. Storage at 20C or 15C resulted in similar (P>0.05) spermatozoal motility. Two fertility trials compared the use of SM and NFDMS-glucose extenders. Embryo recovery 6 days post-ovulation (Experiment 3) and pregnancy rate 50 days postestrus (Experiment 4) was similar (P>0.05) for mares inseminated with spermatozoa extended in SM or NFDMS-glucose.