Retained Placentas In Mares
Written by Dr. Frederick Harper, 
Agricultural Extension Service, University of Tennessee

     When a foal is born without complications, the horse breeder relaxes. But, there's an additional event to be concerned about - passing of the placenta. Don't relax too soon.
     Expulsion of the placenta marks the end of the third, and final stage of labor. Myometrial contractions begin at the tip of the mare's uterine horn, expelling the placental membranes. Actually, the allantoic surface is on the outside of the expelled placenta. While this is occurring, mares may show signs of mild colic, being uneasy, pawing, lying down and rolling.
     The placenta is usually passed within 30 minutes to three hours after birth. If not passed within three hours, it is considered a retained placenta, and requires veterinary attention. All or part of the placenta (allantochorion) may be retained, which occurs in about 11 percent of foaling mares.
     Older mares (15 years old and older) retain placentas more frequently than younger mares. Retained placentas are more likely to occur after dystocias, prolonged gestations and cesareans.
     A retained placenta can result in metritis, laminitis (founder), septicemia or even death of the mare. Once a mare retains a placenta, she is likely to do it again. Poor body condition or poor environment may increase the incidence of retained placentas. Mares that retain a placenta usually do not have the normal "colicy" signs associated with the passing of the placenta.
     A placenta protruding from the mare's vulva and touching her hocks should be looped through itself and tied with binder twine. This keeps the mare from stepping on it, causing it to tear, leaving a pierce in her uterus, and keeps her from kicking it in fright, injuring her foal, Even a small portion of the placenta remaining in the mare is a serious threat. one may not know that this condition exists unless the placenta is carefully examined.
     When a mare expels the placenta, place it in a garbage bag and put it in a refrigerator or cool place for your veterinarian to examine. it is important that there is only one opening in the placenta, the one through which the foal came. A second opening indicates that a piece of the placenta may still be in the mare.
     Never remove a placenta manually, which can cause permanent damage to the endometrium. Oxytocin is apparently the most beneficial treatment. Antibiotics should be given to mares with dystocias, retained placentas for more than 12 hours, a history of post-foaling laminitis, fever, or a stinking discharge.
     Since mares with a history of retaining placentas are likely to do it again, treated them with oxytocin immediately after birth. Wait about 25 days before breeding mares which have had retained placentas.
     Your veterinarian can also determine if the placenta is healthy. An unhealthy or diseased placenta can indicate a potential problem with a new born foal.