Insemination results with slow-cooled stallion semen stored for approximately 40 hours.

Semen from 3 stallions was extended using 2 methods (Kenney extender and a modified Kenney extender), slowly cooled, and stored for 41 +/- 6 (s.d.) h before insemination. An insemination dose (40 ml) contained 1.5-2 billion spermatozoa. In the experiment, 26 mares were inseminated in 30 cycles. The pregnancy rate per cycle obtained with sperm stored in the Kenney extender was 87% (n = 15). When the semen was extended with the modified extender, centrifuged and stored, the pregnancy rate was 60% (n = 15). Inseminations were done every other day until ovulation was detected. If a mare ovulated more than 24 h after the last insemination, she was inseminated also after ovulation. The single-cycle pregnancy rate was 58% when the mares were inseminated only before ovulation (n = 19) but the rate was 100% when the inseminations were done both before and after ovulation (n = 9) or only after ovulation (n = 2). The difference in pregnancy rates was significant (p < 0.05), indicating that postovulatory inseminations probably serve to ensure the pregnancies. The extending and handling methods used in this study resulted in a combined pregnancy rate of 73%, and appear thus to be useful for storing stallion semen for approximately 2 days.