Time and length of estrous periods in mares are highly variable. It is very important to work with a veterinarian who is well-versed in reproduction or a good stallion/mare manager familiar with ultrasound and time breedings. That said, here are some general recommendations.
A mare's gestation period is about 335 to 340 days. She will enter foal heat about seven to nine days after foaling, which generally will last for three days (sometimes longer). Mares typically will ovulate on the third or fourth day of estrus (ovulation is related to the end of estrus, not the onset). After foal heat, she should enter a normal estrous cycle, 21 to 23 days from her last ovulation.
