Tall fescue is a common grass species that makes up more than 40 million acres of pasture in the United States. This grass is commonly infected with a fungus capable of producing the ergot alkaloid ergovaline, an agent responsible for late abortion, prolonged gestation, dystocia (difficult birth), and agalactia (poor milk let-down) in broodmares, reduced growth rates in young horses, and increased respiratory rates in equine athletes recovering from exercise. To better understand how infected tall fescue seed impacts equine athletes, a research team from Missouri State University (MSU) set out to determine if the consumption of infected tall fescue seed adversely affected the recovery of horses exercising under hot and humid conditions.

Lead researcher Gary W. Webb, PhD, PAS, a professor at the MSU William H. Darr School of Agriculture, and colleagues assigned 10 Quarter Horses to one of two different treatment groups; the horses consumed either endophyte-infected or endophyte-free tall fescue seed with a predetermined grain ration twice daily. The team also offered the horses alfalfa hay throughout the study period. The horses remained in treatment groups for 35 days before switching treatments for another 35 days. Researchers measured the horses’ water consumption twice daily and collected urine during Weeks 4-5 and 9-10 to verify adequate alkaloid consumption.

All study horses exercised five days a week during the study period; exercise included cutting work with a mechanical cow. All horses performed two different standardized exercise tests (SET) during Weeks 3, 5, 8, and 10. The anaerobic SET consisted of 10 minutes of warm-up, then horses were required to stop and turn 40 times in a four minute period, simulating cutting work. The aerobic SET consisted of four minutes of walking, 10 minutes of trotting, and 11 minutes of loping in both directions. Researchers measured horses’ rectal temperature, heart rate,