Pregnant Mare That Does Not Have Sufficient Milk or Udder Development
History. A 13-year-old pregnant Arab mare is due to foal in the next week, based on breeding dates. This is her second foal; the first foal did well. She has had limited udder development.
The mare is current on vaccinations and deworming; she has no previous medical problems. She has been on pasture with all the other horses. She is supplemented with 2 pounds of 14% mare and foal feed per day. She is given grass hay, and she is in good body condition. The farm is located in eastern Tennessee.
Clinical Examination. The mare is pregnant. The foal is viable based on movement and heartbeat. The foal is in the pelvic inlet, indicating that the mare will foal soon. All other parameters of the examination are normal. The mare is in good body condition.
Comment. With a mare close to parturition that has had limited udder development, one concern is whether the mare has been fed fescue. The owners are asked about this and say that she has been receiving a grass hay with fescue in it. They did not know that fescue could cause problems. The clients are informed that fescue can contain an endophytic fungus, Neo- typhodium coemophiαlιmι. which produces alkaloid toxins. These toxins are dopaminergic and inhibit prolactin. Additionally, the increase in dopamine activity directly decreases prolactin. Normally» neurons in the proventricular nucleus would release prolactin, which would stimulate lactogenesis. In some animals, progesterone levels are also decreased.
Treatment. Domperidone can be given because it inhibits the dopaminergic effects. If domperidone is started 5 to IO days before parturition, this is often sufficient time for the mare to develop sufficient milk for the foal. If domperidone is not started until up to 24 hours after foaling, it must be given for 10 to 14 days. Some mares will respond and will increase the milk production, whereas some mares do not respond. Although this treatment is often useful in stimulating milk production by the mare, it does not necessarily reverse other complications associated with fescue. Mares that have been given fescue may have foals that appear dysmature, are weak, or have prolonged gestation. The placenta from these affected mares is often thickened. To prevent these effects of fescue, clients are encouraged to keep the mares off fescue-containing feeds for at least 30 to 60 days before foaling. In addition, endophyte-free fescue grasses are available, but expensive.