The pregnancy rate for both groups of mares was the same. The percentage of progressively motile sperm was greater in the semen cooled for 24 hours than that cooled for 48 hours. But the total number of progressive, motile sperm wasn't different whether mares were inseminated once or twice. When sperm interacts with the epithelial cells of the oviduct, the viability of sperm is prolonged up to 96 hours for fresh semen and 72 hours for cooled semen. This study showed that storing semen in the mare worked as well as keeping it in a cooled container.
Stallions differ in the viability and progressive motility of their stored sperm.
So the shipped, cooled semen of all stallions may not give these same results. If the stallion is highly fertile and the mare has been prepared to ovulate within 24-72 hours after insemination, use both doses of semen the day it arrives. This saves the cost of a second trip for a veterinarian or technician to inseminate the mare again and reduces the risk of infection. Each time a mare is inseminated or mated, contamination can lead to an infection. Late in the breeding season, consider using both doses of shipped, cooled semen the day it arrives.