By Dr. Robert Hunter, DVM
Understanding the Foal Heat Cycle – After giving birth, most mares will have the first ovulation in about half the time of a normal heat cycle. The onset of this “foal heat” can vary with each mare from 5 to 16 days. The mare most commonly ovulates on or about the ninth day post foaling. The mare’s postpartum uterus undergoes significant changes. Placental fluid and lochia (debris) is expelled, and the tissue lining of the uterus regenerates while the size of the uterus decreases. During this process, the mare’s muscles are contracting in the walls of the uterus, directing the contents toward the cervix and outside. Mares may lie down and roll on the day of and after foaling due to the strong contractions and discomfort.
Most mares experience inflammation in their uterus during the first week postpartum, and can be cultured during the foal heat to determine if infection is present. The presence of uterine bacteria is a significant cause of reduced fertility. The mare should be cultured after foaling even if you are not breeding her the same year. If a mare carries an infection for one year or more, it will greatly reduce her fertility in the future and be much more costly and difficult to clear up.
In general, veterinarians suggest that mare owners breed mares during the foal heat period. Of course, this follows an examination by your veterinarian to assess possible postpartum complications from a dystocia, retained placenta or prolonged discharge, and other symptoms that would jeopardize the new pregnancy. The rate of conception on a foal heat cycle is comparable to breeding on the second (30-day) cycle, and this can be improved by choosing to artificially inseminate rather than natural breeding.
Some mares will go into a postpartum lactational anestrus where they will not cycle as long as the foal is nursing. If this occurs, there is nothing that will consistently help other than weaning the foal.
There are many new and advanced techniques that a Sacramento vet may use for enhancing the stallion’s or mare’s fertility. Understanding your mare’s cycles and recommendations from your veterinarian will give you the guidance you need to know when to breed back your mare. Your vet will also advise you on the impact of foal heat breeding to your new foal.
Whether you have a professional breeding operation, or a single mare, following the advice of your Sacramento vet will improve your mare’s prospects for good health throughout her life.