Is tall fescue safe for horses after a freeze? New research suggests that toxic tall fescue may retain potentially dangerous concentrations of ergovaline even after extended periods of snow, ice, and freezing temperatures.
For years, many horse owners assumed that several hard freezes made endophyte-infected tall fescue safer. However, University of Kentucky researchers detected elevated ergovaline in a pasture after more than two weeks beneath snow and ice. Their findings suggest that horse owners should not rely on the calendar, cold weather, or the appearance of dormant grass when evaluating tall fescue safety.
In this video, we explain:
• Why endophyte-infected tall fescue can be toxic to horses
• How ergovaline and other ergot alkaloids affect the equine body
• Why pregnant mares and unborn foals face the greatest risk
• How tall fescue exposure can contribute to prolonged pregnancy, inadequate milk production, thickened placentas, difficult foaling, and red-bag deliveries
• Why freezing temperatures may not eliminate the danger
• The differences between toxic, endophyte-free, and novel-endophyte tall fescue
• How pasture testing can help owners assess current risk
• What to do if a pregnant mare has grazed questionable tall fescue
Tall fescue toxicosis in pregnant mares can cause prolonged gestation, poor udder development, little or no milk production, difficult delivery, premature placental separation, weak foals, and stillbirth. Because a red-bag delivery can deprive the foal of oxygen, suspected exposure during late pregnancy should be discussed with a veterinarian before the mare begins showing obvious problems.
Not all tall fescue is equally dangerous. Endophyte-free and carefully selected novel-endophyte varieties may offer safer alternatives, but the different types can look nearly identical. Testing for endophyte infection and measuring ergovaline concentrations are not the same thing, and a single test result should not be considered a permanent guarantee of safety.
The most important takeaway is simple: traditional toxic tall fescue should not be assumed safe merely because the pasture has frozen or been covered by snow. Current pasture testing, planting records, available forage, grazing conditions, and veterinary guidance provide a more reliable basis for managing risk—especially when pregnant mares are involved.
Do you have tall fescue in your horse pastures? Have you ever tested your grass for endophytes or ergovaline? Share your experience in the comments. We respond to all comments.
CHAPTERS
00:00 Is Tall Fescue Safe After a Freeze?
00:38 Why Tall Fescue Can Become Toxic to Horses
03:30 Tall Fescue Toxicosis in Pregnant Mares
06:08 Why Winter Weather May Not Remove the Risk
08:40 Toxic, Endophyte-Free, and Novel-Endophyte Fescue
10:00 How to Test and Manage a Tall Fescue Pasture
This video is intended for general education and is not a substitute for veterinary or professional pasture-management advice. Contact your veterinarian promptly if a pregnant mare has been exposed to suspected toxic tall fescue.
SOURCES
[1] University of Kentucky researchers via Equine Disease Quarterly, “When Is Tall Fescue Safe? Researchers Say the Answer Is Changing”:
https://paulickreport.com/horse-care-category/when-is-tall-fescue-safe-researchers-say-the-answer-is-changing
[2] University of Kentucky, “Tall Fescue Sampling Guidelines for Ergovaline Analyses”:
https://forages.mgcafe.uky.edu/sites/forages.ca.uky.edu/files/tall_fescue_sampling_guidelines_for_ergovaline_analyses%20updated%20April%202024.pdf
[3] American Association of Equine Practitioners, “10 Tips for Fighting Fungus-Infected Fescue”:
https://aaep.org/resource/10-tips-for-fighting-fungus-infected-fescue/
[4] University of Kentucky, “Pregnant Mares Grazing a Novel Endophyte-Infected Tall Fescue”:
https://scholars.uky.edu/en/publications/pregnant-mares-grazing-a-novel-endophyte-infected-tall-fescue-foa/
#TallFescue #HorseHealth #HorsePasture
This video is for educational purposes and constitutes Fair Use under Section 107 of the US Copyright Act of 1976. Allowance is made for “Fair Use” for purposes of education, research, criticism, comment, and news reporting. This video is fully transformative and created in accordance with YouTube’s Content Reuse Policy under the Content Reuse Act. It includes original narration, commentary, educational context, visual edits, and added value through storytelling and analysis. No content is simply re-uploaded.
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