In the spring of 2001, hundreds of mares in Central Kentucky lost their pregnancies in peculiar abortions attributed to mare reproductive loss syndrome (MRLS). Since then, horse farm managers have gone back to square one in reviewing their pasture management practices.

One certain result is they have developed a greater awareness of what’s lurking in the grass. These farm managers have learned that tall fescue is not the only grass commonly used in pastures that might contain an endophyte, an internal fungus that lives inside a plant and is species specific. Some perennial rye, the cool season rye many horse farms in the cooler regions of the country include in their pasture seed mix, also can contain an endophyte