Trifolium pratense (red clover) may become infected with the fungus Rhizoctonia leguminocola(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, and it is stable in dried hay and probably in silage. Horses are highly sensitive to slaframine, but clinical cases occur in cattle as well. Profuse salivation (salivary syndrome) develops within hours after first consumption of contaminated hay; signs also include mild lacrimation, diarrhea, mild bloat, and frequent urination. Morbidity can be high, but death is not expected, and removal of contaminated hay allows recovery and return of appetite within 24–48 hr. 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 “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 GI 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.
Last full review/revision December 2014 by Gary D. Osweiler, DVM, MS, PhD