Prolonged Gestation: Is Fescue Toxicosis a Possibility?

Q. My mare was bred more than 390 days ago and still has not delivered the baby. She's showing signs she’s in foal, including having a large belly. However, her teats and udders are not full. I suspect fescue grass poisoning/toxicity is delaying the foaling. Is this possible? Should I give her domperidone?

Ahmed via e-mail

A. First, I would recommend an exam by your veterinarian to make sure the mare is in foal or that the possibility of a later breeding date is out of the question. (Average gestation in horses is 320 to 362 days.)

Fescue toxicosis can cause an array of problems in mares, one being prolonged gestation, as is possible in this case. This is a problem because the fetus continues to grow in-utero and can result in dystocia (difficult birth). Foals born after prolonged gestation can appear immature despite their extended time in the uterus.

Fescue toxicosis can also cause premature placental separation (red bag), thickened placenta, retained placenta, and suppression of lactation/mammary development, as might be the case here. The best form of treating fescue toxicosis in horses is preventing the mares from eating endophyte-infected contaminated tall fescue.

Domperidone is a pharmaceutical available to help reduce the adverse effects by preventing ergovaline (a toxin) from inhibiting prolactin release and, hence, prevents agalactia (absence of milk). My advice: Have a veterinary evaluate fetal viability and placenta thickness. Your veterinarian will discuss the best course of action for the mare.

About the Author

Carlos M. Gradil, DVM, PhD, MS, Dipl. ACT

Carlos M. Gradil, DVM, PhD, MS, Dipl. ACT, is a reproductive specialist at the University of Massachusetts-Amherst’s College of Veterinary and Animal Sciences where he is the equine studies program coordinator and an extension professor. He teaches courses in equine disease and health management, fundamentals of reproduction, and reproductive physiology. Gradil’s research includes fertility in both horses and dogs.

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