Every breeding season we have a few mare owners that want to breed older maiden mares. A maiden mare is a mare that has never had a foal. These mares may have been busy performing for the first part of their life and now the owners would like to get a foal. Many owners feel this should not be a problem because the mares should be just like young maiden mares and not have any uterine pathology. However, Dr. Jonathon Pycock indicates that there is a good possibility that older maiden mares may have difficulty conceiving. Even though these mares have not been bred, aging changes still occur such as glandular degeneration and endometriosis.
Also, many of these older maiden mares have excessive uterine fluid and excessive uterine fluid has been shown to be a cause of reduced fertility. One cause of excessive uterine fluid is a tight cervix that is unable to dilate properly and prevents normal uterine drainage. These mares generally have no signs of inflammation in the uterus but fail to get pregnant and accumulate fluid in the uterus. If there is more than 1 cm of fluid in the uterus during heat, oxytocin should be used to get rid of this fluid. If there is greater than 2 cm of fluid seen on ultrasound, the uterus may need to be drained and flushed. If there is significant uterine fluid 18 hours after breeding, then the mare can be considered to have delayed uterine clearance. Along with oxytocin and uterine flushing, a prostaglandin such as cloprostenol can be used to decrease the volume of uterine fluid. Cloprostenol actually lasts longer than oxytocin but Dr. Pycock indicates it should not be used after breeding. If you have a maiden mare that has not gotten pregnant, consult your vet for an exam.