Perennial ryegrass staggers
This seasonal condition is caused by lolitrem, a fungal toxin that’s produced by an endophyte fungus found in ryegrass pastures. Ryegrass staggers is therefore different from "staggers" in cows, which is due to hypomagnesaemia.
Endophyte fungi flourish in the summer and autumn when it is warm, especially in more humid areas of the paddock. 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 flightier to handle and/or ride and are sensitive to sudden movements and noise. Severely affected animals show fine tremors, severe head nodding, ear flicking, splaying of legs and may stumble, stagger, fall or become recumbent. Signs are generally made worse by stimulation.
Recovery relies on the removal of the animal(s) from the contaminated pasture to a ‘safe' paddock or yard. The time for full recovery is variable depending upon the 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 pastures containing only endophyte safe ryegrass seed (a type of ryegrass that contains a modified endophyte strain which does not produce ryegrass staggers). Make sure that horses don’t graze the grass down too short so that the lower, more risky leaf-sheath part of the plant is not ingested. Feed horses hay instead of grass, but make sure that the hay doesn’t contain lolitrem. Hay made from affected pasture may still contain the toxin, which may still be viable in the hay.
There is also a vast range of products that may help treat or prevent ryegrass staggers by binding the toxins that are present in the gastro-intestinal tract. These products are fed to at-risk animals to minimise toxin absorption, but they do vary in their claims, cost and effectiveness. It is therefore important to always keep an eye on your horse and its behaviour.
Besides ryegrass staggers, there is a range of things that can cause a horse to act more fractious or nervous than usual. If you think your horse may be acting suspicious or becomes too much to handle, please don’t hesitate to contact us so we can help you out!