Fall Panicum (Panicum dichotomiflorum) Hepatotoxicosis in Horses and Sheep

Abstract

Background: Fourteen horses at a boarding stable in Virginia were diagnosed with hepatic disease and locally grown hay was implicated as the cause.Hypothesis: Panicum dichotomiflorum, the predominant grass species in the hay, is hepatotoxic to horses. Animals: Naturally occurring cases were adult horses of various breeds. Two healthy adult horses and 2 healthy adult sheep were used in feeding trials.Methods: Blood and liver specimens collected from affected animals during the outbreak were analyzed. Some of the affected animals were treated supportively; the main intervention was hay withdrawal. Feeding trials were not blinded and no treatments were provided. Blood and liver specimens were collected and analyzed throughout the trials.Results: Five affected animals were euthanized, whereas the others recovered. One research horse was euthanized for postmortem examination, and the other research animals recovered after hay withdrawal. All affected animals had evidence of hepatic disease with abnormally high aspartate aminotransferase (AST), sorbitol dehydrogenase (SDH), gamma glutamyl transferase (GGT), and alkaline phosphatase (ALP) activity. Evaluation of liver biopsy specimens disclosed mild lymphocytic and histiocytic inflammation, mild vacuolar change (hydropic degeneration), prominently clumped chromatin, and necrosis of individual hepatocytes.Conclusions and Clinical Importance: Severe hepatotoxicosis developed rapidly after Panicum hay exposure. Patchy hepatocyte necrosis was observed, implicating apoptosis as the mechanism of hepatotoxicosis. Absence of fibrosis in the research animals indicates that immediate withdrawal of Panicum hay should allow all but severely affected animals to recover from acute exposure.

Pasture-associated Liver Disease in Horses

“…Hepatic toxicity from ingestion of hay containing fall panicum (Panicum dichotomiflorum) has been documented in multiple horses in a boarding stable 15 and has been reported in horses grazing the grass. 16 Horses naturally intoxicated and two horses experimentally intoxicated developed signs of liver disease, including icterus, lethargy, anorexia, and weight loss, after the horses had been eating the contaminated hay for 2-3 weeks.…”

“…The prognosis is fair to poor with 5 of 14 horses in one published report being euthanized due to clinical deterioration. 15…”

Hepatic diseases in horses

“…Details of hepatic toxicosis because of the consumption of P. coloratum in horses (Cornick et al., 1988) and sheep (Bridges et al., 1987) have been published in the late 80s. Recently Johnson et al. (2006) have reported a clinical case on hepatotoxicosis in 14 horses fed with fall panicum hay ( Panicum dichotomiflorum ) in USA.…”

Fall panicum (Panicum dichotomiflorum) toxicosis in three juvenile goats

“…In Virginia, hepatic disease in horses was associated with P. dichotomiflorum –containing hay. 9 The affected horses were icteric and anorectic, with serum hepatic enzyme elevation. Photosensitization was not observed, although indoor housing and season were factors lowering solar exposure.…”

“…5 Steroidal saponins have been determined to be the likely toxic principle, and can be detected in plant samples associated with outbreaks of toxicosis manifesting in photosensitization and liver disease, including crystal-associated cholangiohepatopathy, icterus, and elevation of serum hepatic enzymes. 2,9,11 It is thought that the bile duct crystals characteristic of poisoning are formed by glucuronic acid–conjugated sapogenin metabolites combining with Ca 2+ to form an insoluble salt. 8,14 Many aspects of Panicum toxicosis are incompletely understood, particularly the conditions surrounding its sporadic occurrence and potential mechanisms contributing to hepatic damage.…”