Camelidae and Cervidae Ryegrass Staggers – NAVLE Study Guide

Overview and Clinical Importance

Ryegrass staggers is a neurological syndrome affecting grazing livestock caused by ingestion of perennial ryegrass (Lolium perenne) infected with the endophytic fungus Epichloë festucae var. lolii (formerly Neotyphodium lolii). The fungus produces tremorgenic mycotoxins, primarily lolitrem B, which causes characteristic tremors, ataxia, and incoordination in affected animals.

Camelids (alpacas and llamas) and cervids (farmed deer) are highly susceptible species commonly affected in regions where perennial ryegrass pastures predominate, particularly New Zealand, Australia, and increasingly in the United States. Young animals under 2 years of age appear most susceptible, and some genetic predisposition exists.

Etiology and Pathophysiology

Causative Agent

The condition results from ingestion of perennial ryegrass infected with the endophytic fungus Epichloë festucae var. lolii. This fungus lives entirely within the plant, growing intercellularly, and cannot spread from plant to plant in the field. Transmission occurs only through infected seed. The fungus-grass relationship is mutualistic: the fungus provides the plant with enhanced insect resistance and drought tolerance, while the grass provides nutrients and habitat.