Rye grass staggers in horses

Article from RD1's 'Straight from the Horse's Mouth', February 2010

Late summer and early autumn brings an increased risk of ryegrass staggers in susceptible pasture.

New Zealand researchers made the breakthrough in this debilitating nervous condition over 25 years ago by discovering that tiny fungi, called endophytes, were the cause of ryegrass staggers in pastures.

They discovered that mycotoxins, produced by some endophytes living within ryegrass cells, could affect livestock, causing them to tremble and affected their muscle co-ordination. This condition is not selective to just horses; it is also commonly diagnosed in other farm animals such as cattle, alpaca, sheep and deer.

This breakthrough discovery paved the way for developing strategies to minimise the nerve and muscle disorder. These strategies include the use of low-endophyte grass varieties to minimise animal's exposure to the toxins. More recently, effective binding agents have come on the market that helps mop up the toxins, therefore allowing the affected animals to excrete them in their faeces.

In recent years, evidence has been mounting that the affect of the toxins on horses may be more widespread than originally thought.

While the trembling and staggering makes severe cases easier to diagnose, many owners believe that behavioural problems which have inexplicably developed in some horses have been caused by mycotoxins. The evidence at this stage appears to be largely anecdotal.

There is no doubt that horses show a wide variation in their susceptibility to mycotoxins. For example, two horses grazing on the same pasture, and presumably ingesting similar quantities of mycotoxins, could well result in one suffering a severe case of staggers, while the other shows no obvious symptoms.

Horses forced to graze on pasture that is already grazed down will be eating mostly the base of the plant. This will likely result in higher consumption of mycotoxins.

There can also be a problem in the warmer months, when the ryegrass has developed seed heads which the horses will happily eat. The problem can continue well into autumn.

Therefore, it is essential to reduce the toxin intake as it has a cumulative effect. The more toxin in a horse's system, the worse its symptoms will be.

Ryegrass staggers is only fatal in the most severe of cases. Most horses will be 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.

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