Endophytes are fungi that live inside some grass plants, most commonly tall fescue and perennial ryegrass. They have a symbiotic relationship with the grass plants they inhabit — thanks to endophytes, infected grasses have increased growth rates, increased drought tolerance, and resistance to certain insects. Unfortunately, these fungi also produce toxins that can affect livestock health.
Signs of fescue toxicosis in ruminants such as goats result from the vasoconstrictive properties of the main toxic agent, ergovaline. Signs can include lameness, reduced appetite, weight loss, reduced fertility, decreased milk production, elevated temperature, unthriftiness, poor rates of gain, and gangrenous tails, feet, or ears ("fescue foot"). "Rye-grass staggers" is another form of endophyte toxicity. Most affected animals show no signs of illness unless excited, at which time they may show tremors, incoordination, and falling down. Some turfgrass varieties of fescues and ryegrasses have high levels of endophytes. If you feed seed screenings from these grasses, make sure to have the seeds tested first. Endophytes do not change the appearance of infected grasses, so suspected feeds must be analyzed for endophytes through laboratory tests.
Endophytes are only transmitted through seeds and the whole life cycle is contained within the affected plant. It is, therefore, fairly easy to prevent fescue toxicosis:
Contact your local Cooperative Extension office for information about testing hay, pasture, or seed for endophytes.
Diagram used from Endophytes help plants, harm animals.