Fall panicum (Panicum dichotomiflorum) hepatotoxicosis in horses and sheep.
Authors: Johnson A L, Divers T J, Freckleton M L, McKenzie H C, Mitchell E, Cullen J M, McDonough S P
Journal: Journal of veterinary internal medicine
Summary
# Fall Panicum Hepatotoxicosis in Horses and Sheep An outbreak of liver disease affecting fourteen horses at a Virginian boarding stable was traced to locally grown hay contaminated with fall panicum (*Panicum dichotomiflorum*), a grass species previously unreported as a hepatotoxin in equines. Researchers characterised the condition through clinical and pathological examination of affected animals during the outbreak, supported by controlled feeding trials in two healthy horses and two sheep given contaminated hay, with serial blood work and liver biopsies collected throughout the exposure periods. All affected animals demonstrated markedly elevated hepatic enzymes (AST, SDH, GGT, and ALP), whilst liver biopsy revealed hepatocyte necrosis, lymphocytic and histiocytic inflammation, and hydropic degeneration—histological findings consistent with apoptosis-driven cell death rather than degenerative changes. Five of the naturally affected horses were euthanised, but critically, research animals and the remaining outbreak cases recovered following immediate hay withdrawal, with the absence of hepatic fibrosis indicating that acute hepatotoxicosis from fall panicum is potentially reversible if exposure ceases promptly. For practitioners, this work establishes fall panicum as a significant forage contaminant requiring vigilance during hay procurement and storage; recognition of acute hepatic enzyme elevation in multiple animals at the same facility should prompt urgent investigation of feed sources, as early hay removal appears to be the decisive intervention preventing mortality in all but the most severely compromised individuals.
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Practical Takeaways
- •Remove Panicum dichotomiflorum-contaminated hay immediately if hepatic disease outbreak occurs—most animals will recover if exposure is stopped early
- •Monitor liver enzyme profiles (AST, SDH, GGT, ALP) in horses with unexplained ill-thrift or depression, particularly if fed locally sourced hay of uncertain composition
- •Inspect hay for Panicum dichotomiflorum (fall panicum grass) and source hay from reputable suppliers to prevent herd exposure to this hepatotoxic species
Key Findings
- •Panicum dichotomiflorum hay caused acute hepatotoxicosis in 14 horses at a boarding stable with elevated liver enzymes (AST, SDH, GGT, ALP)
- •Liver histopathology revealed patchy hepatocyte necrosis, mild lymphocytic inflammation, and hydropic degeneration consistent with apoptosis-mediated toxicity
- •Immediate hay withdrawal resulted in recovery in most affected animals, with no fibrosis observed in research animals indicating reversible acute injury
- •Experimental feeding trials in 2 horses and 2 sheep confirmed rapid development of hepatotoxicosis after Panicum hay exposure