PERENNIAL RYEGRASS TOXICOSIS (RYEGRASS STAGGERS)

Dr Geoff Irish
2 hours ago
3 min read

By Dr. Geoff Irish, Senior Technical Manager

UMMER 2026

Perennial ryegrass toxicosis (PRGT), more commonly known as Ryegrass Staggers, can be a serious problem in livestock grazing perennial ryegrass pastures during the summer and autumn months. It is most commonly seen in sheep and cattle, but horses, deer and alpacas are also susceptible.

Affected animals develop muscle tremors and incoordination, which worsen with stress and external stimuli. Less obvious signs may include ill-thrift, especially in young stock, heat stress, scouring and dags, reduced fertility, and lowered milk production. Deaths can also occur due to mishaps caused by lack of coordination, such as drowning in creeks and dams.

As symptoms are aggravated by physical stress, such as mustering, and external stimuli such as humans, dogs, vehicles and other sources of noise, animal husbandry and health control programs are frequently disrupted, as stock cannot be moved or handled. Shearing, crutching, drenching, jetting and removal of rams may all have to be postponed. Affected stock cannot be sold until they are free of symptoms.

Ryegrass Staggers is caused by toxins produced by an endophyte fungus (Neotyphodium lolii) that lives in perennial ryegrass (Lolium perenne). This fungus grows within the leaves, stems and seeds of perennial ryegrass and produces alkaloids that can have toxic effects on grazing livestock. These toxins accumulate in the plant, peaking in summer and autumn. Neither the fungus nor the toxins adversely affect the plant. In fact, the presence of the fungus benefits the plant by enhancing seedling vigour, tillering, seed production, and resistance to drought and insect pests.

Toxin production is usually highest when the ryegrass goes to head during new-season growth following summer rains. The toxins are concentrated in the seedhead, stem and crown of the plant, but are present at lower levels in the leaf.

Lolitrem B and ergovaline are the two main toxins produced by the endophyte fungus. Lolitrem B is a potent neurotransmitter inhibitor. Once absorbed into the bloodstream, Lolitrem B induces clinical signs such as muscle tremors, incoordination, and other neurological impairments, including a slow, wobbly gait. Ergovaline acts in conjunction with Lolitrem B to increase the severity of Ryegrass Staggers. It primarily causes vasoconstriction, reducing blood flow to the skin and extremities. This reduces the animal’s ability to regulate body temperature, leading to heat stress. Sheep and cattle may seek shade for longer periods, reducing grazing time, and may crowd into dams, troughs and streams in an attempt to cool down, sometimes resulting in mass drownings. Reduced blood flow to the extremities may also aggravate foot problems.

There is no specific treatment for Ryegrass Staggers. The best management option is to remove affected stock from the source of the problem by moving them quietly (without dogs) into another paddock. It is important to avoid stressing affected animals, as this will worsen their condition. Animals typically recover within one to two weeks once removed from the pasture.

To help reduce the risk of Ryegrass Staggers, TRAC Performance Minerals loose-lick supplements (Flock Boost and Bovine Boost) contain a product that binds the toxins produced by the endophyte fungus and can help manage some of the challenges associated with Ryegrass Staggers. They also provide essential salt and other vital minerals and vitamins that are crucial for maintaining animal health.

If you have any questions, please do not hesitate to talk with one of our TRAC Ruminant Experts on 08 8733 1888 or email us at info@totalresult.com.au.