Nearly 25 years ago, New Zealand researchers discovered that mycotoxins produced by endophytes living within ryegrass cells could affect horses and other livestock, causing them to tremble and lose coordination.
The toxins affected part of the brain's cerebellum involved in muscle coordination.
This breakthrough paved the way for development of strategies to minimize the nerve and muscle disorder, which affects horses, sheep, cattle, alpacas, and some species of deer.
In recent years, evidence has been mounting that the effect of the toxins on horses may be more widespread than originally thought.
While the trembling and staggering problems make severe cases easier to diagnose, many owners believe that behavioural problems that have inexplicably developed in some horses have been caused by mycotoxins.
The evidence at this stage appears to be largely anecdotal. While not overwhelming, there is no doubt that a significant body of evidence is building.
Ryegrass staggers is fatal only in the most severe of cases. Most horses become well within one or two weeks once the toxic feed source has been removed from their diet.
Feeding an effective mycotoxin binder, especially one combined with beneficial enzymes and probiotics which enhance the digestibility of starch and sugars as well as promoting a healthy digestive system, is likely to hasten recovery.
Strategies to minimize the risk of ryegrass staggers:
- Use low-endophyte or endophyte-free grasses when resowing pasture. The low-endophyte option is usually best, as endophyte-free grasses do not at this stage tend to compete well with other grass varieties. Local seed merchants should be able to recommend a suitable variety or mix.
- Rotate horses through pasture so they are not forced to eat too close to the base of ryegrass.
- If possible, rotate your horses in such a way that they graze their way through a paddock before ryegrass seedheads form.
- Horses vary widely in their tolerance to the toxins. If you have an annual problem with staggers in your herd, there is a good chance that one or two of your animals will show symptoms first. Watch these animals closely at times when you consider the risk is higher.
- The higher a horse's feed intake, the more susceptible it will be to mycotoxin poisoning. Thus, the risk will be higher with horses that are still growing, those in work, mares in the later stages of pregnancy, and mares feeding foals.
- Watch for visible fungi such as toadstools and mushrooms. When these are growing well, the endophytes within ryegrass are also likely to be doing well.