Naturally occurring tall fescue is often infected with an endophytic fungus, Neotyphotium coenophialum that produces the toxin ergovaline (along with many other compounds). Ergovaline is known to cause many complications with pregnant mares including prolonged gestation, dystocia, mare and foal mortality and agalactia (decreased milk production). While other livestock such as cattle and sheep can be affected by ergovaline, nonpregnant mares, growing horses, stallions and geldings are not know to suffer major negative physiological effects. For each pasture where tall fescue is a concern, two samples are collected and analyzed to determine the risk to broodmares on that pasture:

Endophyte Percentage – Tiller samples collected throughout the pasture are analyzed for the presence of the endophyte, yielding a percent infection rate for a given pasture.  Most pastures containing wild type tall fescue will be 75-95% infected in central Kentucky. Without significant management, infection rates do not change significantly from year to year.  The level of infection, along with the amount of tall fescue present, tells a farm manager the potential of fescue toxicity. 

Ergovaline Concentration – grab samples are representative of what a horse would eat and are analyzed for ergovaline concentration, expressed in part per billion (ppb). Ergovaline concentration changes due to management, time of the year and climatic conditions.  Pastures containing more than 200 ppb in total forage are considered potentially harmful to broodmares in the last trimester and 500 ppb in the first trimester.  This test provides a real time understanding of tall fescue risk to mares and allows managers to remove mares from toxic pastures.