Causes and control of perennial ryegrass staggers in New Zealand

Abstract

Perennial ryegrass staggers, caused by livestock consuming Acremonium lolii-infected perennial ryegrass, is widespread in New Zealand. The disease is particularly prevalent in regions with low summer pasture growth rates, and in stock classes which consume a large proportion of toxic basal ryegrass sheath material. Clinical symptoms may range from slight muscular tremors through to staggering, and collapse. While showing extreme symptoms animals create a stock management problem and are prone to accidental fatalities. These management and economic problems are often exacerbated by the difficult topography, poor access to drinking water and some of the farm management practices adopted by farmers. Evidence increasingly suggests that the subclinical effects are more economically important than clinical symptoms. These include reduced daily weight gains and depression of hormonal levels associated with reproduction and lactation. Small-animal feeding studies confirm the observed effects on animal growth rate, muscular tremors, and indicate abnormal reproductive physiology when feeding on Acremonium-infected ryegrass diets. Control options developed in New Zealand to minimise ryegrass staggers include the utilisation of alternative grass species and encouragement of white clover and other pasture species that are compatible with ryegrass. Other options include alternative grazing management strategies, breeding for ryegrass-staggers resistant animals, development of vaccines which stimulate the animal's ability to metabolise toxins and utilisation of low tremorgen-producing Acremonium fungi. Eradication of Acremonium-infected ryegrass from pastures and re-sowing with Acremonium-free ryegrass seed lines is not a viable option as Acremonium-free ryegrass is less productive and persistent than infected ryegrass.