INSEMINATION RESULTS WITH SLOW-COOLED STALLION SEMEN STORED FOR APPROXIMATELY 40 HOURS

Semen from 3 stallions was extended using 2 methods (Kenney extender a nd 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 insemina ted in 30 cycles. The pregnancy rate per cycle obtained with sperm sto red in the Kenney extender was 87% (n=15). When the semen was extended with the modified extender, centrifuged and stored, the pregnancy rat e was 60% (n=15). Inseminations were done every other day until ovulat ion was detected. If a mare ovulated more than 24 h after the last ins emination, she was inseminated also after ovulation. The single-cycle pregnancy rate was 58% when the mares were inseminated only before ovu lation (n=19) but the rate was 100% when the inseminations were done b oth before and after ovulation (n=9) or only after ovulation (n=2). Th e difference in pregnancy rates was significant (p<0.05), indicating t hat postovulatory inseminations probably serve to ensure the pregnanci es. The extending and handling methods used in this study resulted in a combined pregnancy rate of 73%, and appear thus to be useful for sto ring stallion semen for approximately 2 days.