Ask the Vet: Fescue Toxicity

Q:  Other than not shedding out, what else could you expect to see in fescue toxicity in a gelding? – Jean Thompson

What a fantastic question. Fescue is a type of grass that is common throughout large portions of the United States, especially in the south. Fescue grass can commonly be infected with a type of fungus called an endophyte which is responsible for its toxic effects.  The prevalence of Fescue infected with endophyte varies depending on where you live in the country. The toxic effects of the Fescue endophyte also vary from one species to another.  Cattle and sheep tend to have the most severe problems from Fescue including decreased weight gain, increased body temperature, poor hair coats and necrosis (tissue death) of their feet, tail and ears. Thankfully these symptoms are not reported in horses.  The major problem that is seen with Fescue grass in horses is in brood mares.  Fescue can affect hormones in mares during late gestation causing increase in gestation length, difficult births, and decreased milk production.  It is also thought that foals and yearling eating endophyte infected Fescue may gain weight slower than they would otherwise. For an adult male horse Fescue grass is safe for consumption.  If you have broodmares on your farm you can send samples of grass for laboratory analysis to determine if it is infected with endophyte.  If you find that your grass is infected with endophyte it is recommended to keep pregnant mares from grazing on it during the last trimester (90 days) of their pregnancy. 

If you have a horse that is not shedding out his winter coat, the most common cause is Equine Pituitary Pars Intermedia Dysfunction (PPID or sometimes called equine Cushing’s Disease.) In horses with PPID, the middle lobe of the pituitary gland (pars intermedia) becomes enlarged over time and results in over production of hormones.  PPID is most common in horses over fifteen years old but can sometimes be seen in slightly younger horses. Other symptoms that have can be associated with PPID include excessive drinking and urination (polyuria/polydipsia), laminitis, lethargy, excessive sweating, muscle mass loss and repeated infections such as sole abscesses.  While there is no cure for PPID the drug Pergolide (Prascend) can significantly help with symptoms. If you feel that your horse may have PPID, discuss it with your veterinarian. 

Dr. Wilson is a native of Dripping Springs, Texas. She attended Texas A&M for her undergraduate studies in Biomedical Science and obtained her Doctor of Veterinary Medicine degree in the Spring of 2010. She has particular interests in lameness, internal medicine and surgery. Dr. Wilson joined Austin Equine as our first veterinary intern. She is member of the American Association of Equine Practitioners and the American Veterinary Medical Association. Dr. Wilson is thrilled to be living in the Austin area. Away from work, she is an avid rider and owns Malcolm, a twenty-one year old Thoroughbred.

If you have a question you would like to ASK A VET, please email with the subject: ‘ask a vet’

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