Trifolium pratense (red clover) may become infected with the fungus Slafractonia leguminicola (formerly Rhizoctonia leguminicola) (black patch disease), especially in wet, cool years. Rarely, other legumes (white clover, alsike, alfalfa) may be infected. Slaframine is an indolizidine alkaloid recognized as the toxic principle in fresh clover, and it is stable in dried hay and probably in silage. Horses are highly sensitive to slaframine, but clinical cases also occur in cattle. Profuse salivation (salivary syndrome) develops within hours after first consumption of contaminated hay; clinical signs also include mild lacrimation, diarrhea, mild bloat, and frequent urination. Morbidity can be high, but death is not typical, and the removal of contaminated hay allows recovery and the return of an animal's appetite, usually within 24–48 hours and up to 4 days.
A related alkaloid, swainsonine, produced by R leguminicola, has caused a lysosomal storage disease from prolonged exposure, but its importance in the salivary syndrome is not confirmed. Diagnosis is tentatively based on recognition of the characteristic clinical signs and the presence of so-called black patch on the forages. Chemical detection of slaframine or swainsonine in forages helps to confirm the diagnosis. There is no specific antidote to slaframine toxicosis, although atropine may control at least some of the prominent salivary and gastrointestinal signs. Removal of animals from the contaminated hay is essential. Prevention of Rhizoctonia infection of clovers has been difficult. Some clover varieties may be relatively resistant to black patch disease. Reduced usage of red clover for forages or dilution with other feeds is helpful.
For More Information
Kagan IA. Blackpatch of clover, cause of slobbers syndrome: A review of the disease and the pathogen Rhizoctonica leguminicola. Front Vet Sci 2016;3:3. doi: 10.3389/fvets.2016.00003.