Also Known As
The placenta is a membranous vascular organ that develops in the mare during pregnancy and is expelled as afterbirth once foaling occurs. The placenta lines the uterine wall and partially envelops the fetus to which it is attached by the umbilical cord.
Once the foal is born, the placenta or afterbirth is expelled during the final stage of labor with the aid of uterine contractions. This process usually takes 30 minutes to three hours.
If the afterbirth is retained for a long period of time, a medical emergency may occur because toxins may be released into the blood, producing endotoxic shock.
Membranes that are not expelled within four hours are considered retained and steps should be taken to protect the health of the mare by calling in a veterinarian. Older mares retain placentas more often than younger mares and retained placentas are more likely to occur with difficult deliveries, Caesarean sections, and prolonged gestations. A retained placenta may result in metritis, laminitis, endotoxin, and sometimes the death of the mare.
- Fever, with sweating
- Muscle tremors
- Unusual discharge
A mare that is in poor health or living in an unhealthy environment is more likely to retain afterbirth than a healthy mare in a good environment. A prior history of retained placenta, a difficult delivery, a Caesarean birth, or a prolonged gestation period may also lead to a retained placenta.
Before breeding, the horse owner should make sure the mare is in good health, has the right food, and a comfortable environment. Since mares with a history of retaining placentas are likely to do so again, most veterinarians recommend treating them with oxytocin immediately after birth and breeding again should be delayed for at least 25 days or longer.
Because a retained afterbirth may lead to metritis, laminitis, septicemia, endotoxic shock, or death, calling a veterinarian promptly is important. To be sure that the entire placenta has been expelled, lay the afterbirth on the ground. If the tissue forms an F shape without holes or tears, it is probably fully discharged.
The veterinarian may wan to weigh the placenta which usually will weigh between 10 and 14 pounds, depending on the size of the foal. The placenta may also be filled with water to determine if tears or holes are present meaning that parts of it may have been left in the mare's body.
Retained pieces of placenta could impair future breeding ability or lead to serious infection. Antibiotics should be administered to a mare that has dystocias, which is a placenta that is retained for more than 12 hours after foaling occurs.
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