Description

Toxicosis is a poisoning caused by a chemical mycotoxin. In cases of slaframine toxicosis, the chemical mycotoxin is produced by the fungus Rhizoctonia leguminocola which causes a condition known as ‘black patch disease’ on certain legume plants and has a poisoning effect on horses that eat hay contaminated with the mycotoxin.

The most commonly affected forage is red clover (Trifolium pretense). However, other legumes such as white clover, alsike, and alfalfa can become infected with the fungus.

Horses are particularly sensitive to slaframine and may develop profuse salivation along with other symptoms of toxicosis within 1-3 hours of consuming infected forage. Wet, cool growing seasons create ideal conditions for the fungus, so increased numbers of cases are likely to be seen following wet, cool springs or autumns. The fungus may persist in a pasture for a number of years.

The condition is typically non-fatal and resolves within 24-72 hours of the horse being removed from the contaminated feed source.

Symptoms

• Profuse salivation (salivary syndrome)
• Mild lacrimation (tearing)
• Diarrhea
• Mild bloat
• Frequent urination
• One reported case of abortion in a mare
• Death is unlikely

Causes

Clovers and legumes may become infected with the fungus Rhizoctonia leuminocola which causes ‘black patch disease’ in wet, cool years. The term ‘black patch’ derives from the bronze to black rings that form on the underside of leaves and stems. The fungus can persist in pastures for years.

Slaframine, an indolizidine alkaloid mycotoxin produced by the fungus, causes a variety of typically non-lethal symptoms in the horse. Slaframine can be active in stored hay for 10 months or more. However, the biological activity of the toxin decreases over time.

Fresh hay can contain the equivalent of 50-100 parts per million of slaframine, (ppm) but the concentration will decreases steadily during storage. Any slaframine concentrations above 10 ppm may cause clinical signs.

Prevention

Avoid feeding any clovers or legumes that are infected with the fungus Rhizoctonia leguminocola by having hay tested and watching our for the tell-tale bronze-to-black rings that form on the underside of leaves and stems of affected hay.

Treatment

Diagnosis is tentatively based on the characteristic clinical signs and the presence of “black patch” on the forages. While chemical detection of slaframine in forages helps to confirm the diagnosis, the test requires special laboratory equipment and is generally not cost-effective to perform.

No specific antidote for slaframine toxicosis exists. Treatment primarily includes removing the horse from the offending forage. Occasionally, atropine is used to treat excessive salivation.