Perennial ryegrass toxicosis (or ryegrass staggers) can be a serious and widespread problem in livestock grazing perennial ryegrass dominant pastures during summer and autumn.
Outbreaks of perennial ryegrass toxicity occur annually and are most common in southern Victoria and Tasmania.
In some years serious outbreaks result in devastating losses.
Conditions when perennial ryegrass toxicosis is likely to occur
Perennial ryegrass is the most commonly sown pasture grass in Australia. About 90% of established perennial ryegrass plants are infected with the endophyte fungus Neotyphodium lolii. The fungus is not harmful to the grass, but produces chemicals that can produce toxic effects in livestock.
Conditions under which perennial ryegrass toxicosis is more likely to occur include:
- Summer and autumn.
- When late season rainfall causes abundant pasture growth and the following summer and autumn includes hot spells during the dry period.
- When the main legume in mixed pastures has dried off, been trampled and decomposed leaving the pasture as a pure stand of perennial ryegrass.
Identifying and diagnosing perennial ryegrass toxicosis
The most commonly recognised sign of perennial ryegrass toxicosis is staggering.
Other clinical signs that would lead a producer to suspect perennial ryegrass toxicosis include the following:
- Tremors exaggerated by external stimuli (mustering, humans, dogs, vehicles and other sources of noise).
- Loss of coordination and control over direction of movement, stiff gait, arched back.
- Recumbency, unable to rise, convulsions.
- Deaths resulting from mishaps due to a lack of coordination eg drowning in dams.
Strategies to prevent perennial ryegrass toxicosis
A risk management plan should be prepared on properties with perennial ryegrass dominant pastures in winter rainfall regions, especially if perennial ryegrass toxicosis has been problem in the past.
Pastures can be over sown with vigorous cultivars of legumes and/or other non-toxic grass species to dilute the toxin. The optimum solution to perennial ryegrass toxicosis may be to renovate pastures after first eliminating old perennial ryegrass plants and seeds that contain the 'wild type' endophyte fungus from the environment.
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