This is a very common condition in which breeding causes excessive uterine inflammation, which may interfere with conception and the maintenance of pregnancy. It is more common in older mares that have a reduced ability to clear debris after breeding.

In the normal mare, there is always some inflammation associated with breeding. This is required in order for excessive semen and debris to be cleared from the uterus. If the uterus overreacts, then it may accumulate additional fluid and inflammatory products. This creates an unfavorable environment for the recently fertilized egg and early pregnancy.

Semen causes inflammation normally. In this condition, it elicits a stronger, more allergic type response.

Mares with this problem may require repeated ultrasound monitoring to assess fluid accumulation. It is critical that this problem be identified and treated for successful breeding.