Much of the pasture in Virginia is tall fescue. While this hardy grass is a high quality nutrient source for most horses, it is often infected with an endophytic fungus named Acremonium coenephialum that is toxic to pregnant mares. The fungus produces damaging alkaloids such as ergovaline.
Some results of fescue toxicosis are:
- Late term abortions (death of the fetus), usually in the last 2 months of gestation
- Dystocia (difficult foaling)
- Premature placental separation (red bag delivery) – This is a veterinary emergency and results in lack of oxygen during birth.
- Prolonged gestation in mares (up to 13 months)
- Decreased milk production
- Failure of passive transfer (IgG) in the foal from lack of colostrum production in the mare
- Retained placenta
- Decreased growth rates in young horses if forage is not supplemented with grain
An ounce of prevention is worth a pound of cure! What can you do to prevent fescue toxicity?
- Have your pasture and hay tested to determine the level of infection
- Mow fields prior to the development of seed heads, which contain the highest levels of toxins in the plant
- Remove broodmares from fescue pastures 30 days prior to breeding and a minimum of 60 to 90 days prior to foaling
- Make sure hay does not contain endophyte infected fescue either
- Keep accurate records of breeding and anticipated foaling dates
- Monitor the mare closely during late pregnancy
- Contact your veterinarian if impending signs of birth, including udder development, relaxation of vulva, and muscles around the tailhead fail to develop within the expected timeframe or if these signs develop prematurely
- Attend the birth. If mare fails to show signs of normal birth progression, contact your veterinarian immediately!
- Keep mares and foals off fescue until after weaning to prevent poor milk production