This appears to have been a particularly bad year for ryegrass staggers and cases continue to appear in all classes of cows, sheep and horses.
Ryegrass Staggers (RGS) is one of the most commonly seen neurological conditions in cattle, sheep, horses, deer and alpacas. It should not be confused with Grass Staggers, which is caused by Magnesium deficiency.
RGS is caused by toxins produced by an endophyte fungus which grows in the cells of perennial ryegrass. The fungus has a symbiotic relationship with the grass, which means that the fungus benefits from the grass by obtaining its nutrients from the grass, and the grass benefits from the fungus as it acts as a growth stimulator and insect repellent.
However, the fungus produces a toxin that causes the symptoms we see. The toxin is present in ryegrass all year. However, the toxin levels are highest in the basal sheath (at the base) of the plant so outbreaks generally only occur when feed is in short supply during the summer/autumn.
RGS affects all ages of animals and an outbreak may be seen in several age groups simultaneously, although young animals seem more susceptible. Clinical signs usually develop within 7 to 14 days of cattle being moved to affected pasture.
Presenting signs vary considerably between animals, with some animals apparently unaffected whilst others are unable to stand. Deaths are uncommon and usually occur accidentally when animals fall into streams, off cliffs or drown.
Signs include:
- Difficulty moving
- Head tremors
- Muscle twitching
- Jerky leg movements
- Swaying and staggering with a stiff gait
- Collapse
Clinical signs can be aggravated by heat stress or mustering.
The effects of the toxin are always reversible and do not produce long-term or permanent damage. There are no specific treatments for RGS, and affected animals usually recover in one to two weeks if removed from affected pasture, or given additional alternative feed. Mycosorb is a powder that can be made into a drench, which binds the toxin in the rumen and helps reduce the extent of clinical signs.
Prevention of staggers is complicated because although endophyte (fungus) free ryegrass is available, it has disadvantages compared to standard ryegrass. So called ‘safe’ endophyte strains or endophyte-free strains often grow fungus within three to five years, and are less vigorous than standard ryegrass.
Preventing over-grazing (keeping pastures leafy) and avoiding build-up of dead litter will reduce your incidence of RGS. Other options include feeding grass or maize silage, baylage or brassicas, and or rotational grazing with daily movements of stock. Grazing practices which lead to ryegrass dominance, such as set stocking in summer should be avoided.
