Editor’s Note: This excerpt is from Understanding Equine First Aid by Michael Ball, DVM. 

There are two large arteries that supply the uterus with blood. One crisis that can occur is severe hemorrhage of one of these arteries into the surrounding tissue or abdominal cavity. This problem, “rupture of the uterine artery,” is well-documented in older mares and usually occurs after the birth of the foal or up to a few days afterward. It is suspected that during the birth process the artery ruptures or is torn in varying degrees. The arteries travel in a band of tissue called the broad ligament which helps to suspend the uterus within the abdominal cavity.

If the rupture is small, a hematoma will form within the broad ligament and, hopefully, the ligament will contain the bleeding and the pressure will slow the hemorrhage and allow the artery to clot. If the rupture is large and the blood flow strong, the hematoma can become quite large (basketball-sized) and potentially start to bleed freely into the abdominal cavity. If the hematoma is small, the only clinical sign might be mild colic during the post-partum period and, obviously, if the other extreme occurs the mare could bleed to death in a relatively short period of time.

Signs of more significant hemorrhage would include weakness, significantly elevated heart rate, continued colic, and pale/white mucous membranes. Many mares will experience post-partum cramping and demonstrate some degree of colic, but veterinary evaluation should be performed nonetheless. Mares suspected of uterine artery hemorrhage should be kept as calm as possible and moved as little as possible (cross-tie if necessary). Excessive movement or excitation could hinder blood clot formation