Perennial ryegrass staggers

This seasonal condition is caused by lolitrem, a fungal-produced toxin, found in ryegrass pastures.  The fungus infests the plants and is commonly known as an endophyte fungus (Neotyphodium lolii).

Endophyte fungi grow well in the summer and autumn when it is warm, and the toxins tend to concentrate in the lower leaf sheath, flower heads and seeds, but can be found in all parts of the plant.  Horses inadvertently eat the toxin when grazing, and with shorter grass and hard grazing, larger amounts of the toxin-contaminated pasture are ingested.

Clinical signs may develop 7-14 days after exposure and are the result of the toxins interfering with nerve transmission.  Affected horses can show varying degrees of clinical signs.  Mildly affected horses can become more nervous and spooky to handle and ride, and sensitive to sudden movement and noise.  More severely affected horses may show severe head nodding, splaying of legs and a tendency to stumble, stagger or fall. Fine tremors are usually exacerbated by movement and hind-quarter paralysis can also be observed.

Diagnosis generally relies on clinical signs, environmental conditions and response to treatment. Recovery is usually spontaneous once the animal has been removed from the contaminated pasture to a ‘safe' paddock or yard.  A safe paddock is one that contains little or no ryegrass, or has been sewn with a ryegrass with a modified endophyte.  Endophyte-safe ryegrass seed contains an endophyte strain which does not produce ryegrass staggers (but does confer the advantages of having an endophyte in your pasture such as increased persistence). This can be used to re-sow your paddocks, but there is a risk that the "wild type" endophyte, which causes staggers could re-invade the pasture.  However, a paddock containing plenty of grass so that the horse does not need to overgraze down into the leaf sheath is also satisfactory.

During the recovery period, misadventure is the greatest hazard, so it is important to keep animals quiet and in a well-contained area that is free of hazards such as ditches and dams.  Alternative feeds may be fed such as hay and concentrates, but hay made from the affected pasture should be avoided because the toxin is still viable in the hay.

In addition to the above preventative measures, there are products available that can be fed to at-risk animals that may minimise toxin absorption.  Please speak to your veterinarian before commencing the use of these products, as some are more effective than others.

If you are concerned about your horse, or wish to discuss ryegrass staggers further, please do not hesitate to contact Totally Vets, or call into one of our clinics.

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