Annual ryegrass toxicity

Occurs in annual ryegrass pastures in South Australia and Western Australia.

What to look for

Ranges from mild to severe nervous signs, ie staggering, convulsions, death can occur in severe cases.

Cause

A bacterial toxin spread by a pasture nematode (worm). A tiny nematode invades the developing seed head in annual rye grass and turns it into an abnormal growth called a “gall”. The nematode carries bacteria that multiply rapidly in the gall and produce a powerful toxin that looks like yellow slime. The toxin in the gall is very persistent, so infected pastures will remain toxic until the affected plant material is removed or dies down. Hay made from toxic pastures may also cause ARGT.

Animals likely to be affected

All age groups of cattle are susceptible.

Other diseases with similar clinical signs

Lead poisoning, phalaris staggers or perennial rye grass staggers that occurs on perennial rye grass pastures.

Confirming the diagnosis

Finding of galls and yellow slime on annual rye grass plants. Note that rain can wash the slime off the plants.

Spread of the disease

The disease can be spread beyond the affected region via toxic hay, although it is not clear whether this can lead to establishment of ARGT in new regions.

Treatment

Any stock movement should be done carefully to avoid injuries and worsening of the clinical signs. Affected mobs should be moved quietly to a non-toxic area and supported with free access to water and high quality feed. Animals may continue to show clinical signs of ARGT for up to 10 days after being removed from the toxic pasture.

Prevention

If paddocks are suspected of being infected they can be sprayed out and replaced, or prevent the pasture developing seed heads by topping or hard, persistent grazing. A biological control agent called twist fungus is available commercially, which appears to be effective in reducing toxicity when it becomes established in pastures.

More information

Department of Agirculture WA - Annual ryegrass toxicity in livestock


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