Perennial ryegrass staggers
This seasonal condition is caused by lolitrem, a fungal toxin, produced by an endophyte fungus found in ryegrass pastures and is NOT the same as "staggers" in cows due to hypomagnesaemia. Clinical cases are commonly seen in horses, sheep and calves, but all animals can be affected.
Endophyte fungi flourish in the summer and autumn when it is warm. The toxin concentrates in the lower leaf sheath, flower heads and seeds, but can be found in all parts of the plant. With shorter grass and hard grazing, larger amounts of the toxin are ingested.
Clinical signs can vary but generally develop seven to fourteen days after exposure and are the result of the toxins interfering with nerve transmission. Those mildly affected become more nervous and flighty to handle and/or ride, and are sensitive to sudden movement and noise. Severely affected animals show fine tremors, severe head nodding, splaying of legs and may stumble, stagger, fall or become recumbent. Signs are generally made worse by stimulation.
Recovery relies on removal of the animal(s) from the contaminated pasture to a ‘safe' paddock or yard. The time for full recovery is variable depending upon level and duration of exposure. Misadventure is the greatest risk during this time, so it is important to keep animals quiet and in an area free of hazards such as dams or rough terrain.
‘Safe' pasture could be one containing little or no ryegrass, or be endophyte safe ryegrass seed (contains a modified endophyte strain which does not produce ryegrass staggers). Alternately paddocks containing plenty of grass, so that the animals don't overgraze down into the leaf sheath, can also be satisfactory. Alternative feeds, such as hay and/or concentrates, should be fed, but note that hay made from affected pasture should be avoided because the toxin is still viable in the hay.
Lastly, there is a vast range of products that may help treat or prevent ryegrass staggers. They are fed to at-risk animals to minimise toxin absorption, but they do vary in their claims, cost and effectiveness. So for more advice don't hesitate to give your vet a call!