Can they eat it? / Tall fescue (endophyte-infected)
Can horses eat tall fescue (endophyte-infected)?
Careful, especially for pregnant mares.
Common pasture grass carrying a fungus that causes prolonged pregnancy, thick placentas, no milk and weak foals. Most adult horses tolerate it; mares in late pregnancy should come off it 60 to 90 days before foaling. Endophyte-free varieties exist.
In mares: no bag at foaling, overdue, retained placenta.
Talk to your vet about pasture testing and when to move the mare.
Why
Tall fescue is often colonized by a fungus called Epichloë coenophiala (endophyte). The fungus makes alkaloids, mainly ergovaline, that constrict blood vessels and interfere with dopamine and prolactin signaling. In most horses this causes mild effects like a rough coat, poor performance or heat stress. In pregnant mares it can prolong gestation, thicken the placenta and suppress milk production, leading to weak foals.
How much is too much
There is no single safe-dose number for endophyte-infected fescue, because the toxin level varies by plant, season and stand. For a 1,000 lb horse, grazing a typical pasture is usually tolerated, but a dense stand grazed hard in hot, dry weather carries more risk. Ponies and miniatures can react more strongly, so limit their time on infected pasture. Ask your vet or extension office about testing your stand.
Horses
Most adult horses in work or at pasture tolerate endophyte-infected tall fescue without obvious trouble. Watch for heat intolerance, a rough dull coat, reduced sweating, or lower performance in hot weather. Stands that are stressed by drought or grazed very short tend to carry higher toxin levels. Consider a hay or pasture test if you notice these signs, and talk to your vet about options.
Ponies and easy keepers
Ponies, miniatures, seniors and insulin-resistant or laminitis-prone horses are not the main concern for fescue toxicosis, but they are sensitive to any heavy grass intake. Grass sugars and high-carbohydrate pasture can trigger laminitis, so restrict grazing time and watch for heat or sore feet. Ask your vet whether a grazing muzzle or a drylot is appropriate.
Safe alternatives
Offer endophyte-free tall fescue varieties, orchardgrass, timothy, or a mixed grass pasture for mares. For a mare in late pregnancy, move her to a safe paddock 60 to 90 days before foaling. Hay from an endophyte-free source or tested hay can also be fed in place of infected pasture.
Questions people ask
Is fescue hay as bad as pasture?
Hay can carry the same endophyte and toxin. If you are unsure of the source, ask for a lab test or choose hay from a field known to be endophyte-free.
Can I graze fescue after frost?
Frost does not remove the toxin. Toxin levels can stay high in dormant or stressed fescue, so keep the same caution through the cold months.
My mare grazed fescue and her foal is weak, what now?
Call your vet right away. A weak or overdue foal needs immediate veterinary care, and your vet can advise on the mare and foal together.
Careful for horses means: fine in a small amount, prepared as described, and not for every pet; the details say when to skip it.
General information from veterinary guidance, not a diagnosis. If you are worried, call your vet or a pet poison line: ASPCA Animal Poison Control (888) 426-4435. Charges may apply.
Written by Hoofdeck editors · updated Nov 13, 2026 · from ASPCA Animal Poison Control, Merck Veterinary Manual and university extension guidance.