Grass Staggers in Horses: Perennial Ryegrass and Dallis Grass (Paspalum) Poisoning

by Robert N. Oglesby DVM

Introduction

Incoordination and ataxia are a common clinical finding in horses and can be caused by a number of diseases. When signs include mild excitability and the incoordination is of the spastic (tremors, stiffness, and tetany) variety and it is associated with recently being placed on pasture composed of perennial ryegrass (Lolium sp.), dallis grass, or bahia grass, grass staggers is on the list of possibilities. Having more than one individual in the herd affected further increases the suspicion or grass staggers.

Dallis grass staggers is caused by fungal toxins produced by Claviceps paspali in the seed heads of Paspallims spp. grasses, especially Dallis grass. Other Paspalumlype grasses can be affected including Argentine bahia grass (Paspalum dilatatum) and water couch grass (Paspalum wchiim). Perennial ryegrass staggers is caused by the indole-based alkaloid tremorgenic neurotoxins lolitrems, which are produced when infested with the endophytic fungus Acremomum loliae or Acremonium coenophialum. This article consists of the clinical signs, diagnosis, treatment, and prognosis of horses affected by perennial ryegrass or dallis grass staggers.