These findings suggest that other factors beyond maternal vasoconstriction are likely involved in tall fescue’s effects on the equine fetus. | Photo: Kevin Thompson/The Horse

Researchers know that some types of tall fescue—particularly, those playing host to toxic endophytes called ergot alkaloids—can be bad news for pregnant mares. They know that mares consuming endophyte-infected tall fescue can develop fescue toxicosis, characterized by a lack of milk production, prolonged gestation, placental thickening, and weak or nonviable foals. They even know that ergovaline—one type of ergot alkaloid—can cause vasoconstriction in horses.

What they don’t know is exactly how the ergot alkaloids cause the problems seen in pregnant mares. One theory is that decreased blood flow to the uterus plays a role. Researchers previously determined that feeding horses ground endophyte-infected tall fescue results in vasoconstriction in the distal palmar artery, and such decreased blood flow to the uterus could have an impact.

So, researchers from the USDA Agricultural Research Service’s Forage-Animal Production Research Unit (ARS-FAPRU) and University of Kentucky Gluck Equine Research Center, both in Lexington, set out to evaluate whether a lack of placental bloodflow could contribute to fescue toxicosis development. Specifically, they evaluated how ergopeptine alkaloids (ergovaline, ergocryptine, ergocristine, ergocornine, and ergotamine) and ergoline alkaloids (lysergic acid and ergonovine), two ergot alkaloids found in endophyte-infected tall fescue, impact vasoactivity in the equine palmar artery and vein and uterine artery