Ryegrass Staggers is a nervous disease of sheep, cattle, horses and deer caused by the ingestion of an endophytic fungal toxin associated with ryegrass pastures. When the endophyte grows in ryegrass it produces chemicals; one of which is Lolitrem B that causes summer RGS. Drought can increase chemical concentrations, and fresh growth immediately after a drought can have high amounts. Lolitrem B tends to be concentrated more in the base of the plant and in the seed heads. The toxic effects can be worse under prolonged hard grazing during dry summers as animals graze more into the base of the plant where the toxin concentration is highest. There is no relationship between RGS and grass staggers (hypomagnesaemia) which is a magnesium deficiency occurring mainly in dairy cows.The clinical signs of RGS range from a slight trembling of the head, to swaying or staggering during movement, to inability to stand. Forced movement tends to increase the severity of signs.
A number of grazing strategies can help reduce the impact of endophyte toxins on stock:
- Try to keep the pasture leafy during the seed head phases in late spring. Endophyte is present in the seed heads; grazing them off or topping before they become dominant will reduce the toxin intake by the animal.
- Try not to graze so far into the base of the pasture during warm and/or dry periods. The majority of the toxins are present in the base of the plant, and grazing above this will reduce toxin intake.
- Young stock are more susceptible to RGS than adult stock. Try to keep young stock off prone areas.
- Take special care with new regrowth from ryegrass pastures after a prolonged drought.
- Encourage the growth of clover at all times. This helps to dilute the amount of toxic ryegrass entering the animal. Other species such as chicory have a role to play as dilution species.
- Have special purpose safe pastures available for the summer period. These might be annual crops such as brassicas, or perennial pastures based on certified tall fescue, brome, chicory, etc.
- Hay and silage made from toxic ryegrass will remain toxic. Feed hay or silage made from ryegrass that has low toxin levels at cutting, or use conserved feed made from safe species.
Remove stock as soon as symptoms appear, and provide alternative feeds;Regularly rotate stock, keeping them as quiet as possible;Avoid using paddocks with natural hazards such as rivers and dams;Watch for hawks and seagulls attacking stock suffering the effects of severe staggers.