Lactational anestrus in Caribbean donkeys

Lactational anestrus is common in many species, but not in equids. This case report documents an unusual finding of eight donkeys (from a group of 25) on the Caribbean island of St. Kitts that remained anestrus after foaling during the physiological breeding season. Twenty-five feral female donkeys in advanced pregnancy were acquired. No breeding history was known and all pregnancies were monitored via weekly transabdominal ultrasonography. All jennies foaled without complications and weekly transrectal ultrasonographic examinations were conducted to monitor uterine involution and cyclicity. Four foals died from septicemia within the first week and all of their dams soon re-established ovarian cyclicity. Thirteen jennies had a foal heat with overt signs of estrus within 2 weeks after foaling, then returned to normal cyclicity. However, the remaining eight jennies did not ovulate or display signs of estrus until their foals were weaned, ~4 months later. Following weaning, all eight jennies promptly returned to normal cyclicity. That these eight jennies returned to normal cyclicity following weaning supported our diagnosis of lactational anestrus during the physiological breeding season, a phenomenon apparently never reported in donkeys.