Perennial ryegrass (Lolium perenne
) is a common perennial pasture grass which can cause ryegrass staggers
in horses. The condition is caused by the presence of the fungal endophyte, Neotyphodium lolii
, which produces toxic alkaloids, specifically lolitrem B.
Ryegrass staggers occurs variably, depending on the weather conditions. The toxicity increases during the summer and fall and may remain at high levels for 5 to 6 months. Horses will typically begin to demonstrate signs of ryegrass staggers 7-14 days after grazing the plant. Prolonged exposure to the toxins can cause permanent neurological damage to the animal.
Infected horses may appear normal when left on their own in the pasture, however when asked to move they appear uncoordinated, stiff, weak, and look like they might fall over. Many horses with this condition are found dead due to accidental means such as falling into the water and drowning. Perennial ryegrass can also produce high levels of water-soluble carbohydrates.