Fall panicum (Panicum dichotomiflorum) hepatotoxicosis in horses and sheep.

The article discusses a study in which horses at a Virginia boarding stable developed liver disease due to eating hay made from Panicum dichotomiflorum, a local grass species that is toxic to horses. After withdrawing the hay from their diet, most of the horses recovered, showing the importance of identifying and removing toxic elements from animal feeds.

Research Objective and Methods

• The objective of this research was to investigate an outbreak of hepatic disease in horses caused by consuming Hay made from Panicum dichotomiflorum, a locally grown grass species. This grass is known to harm the liver, a condition known as hepatotoxicosis.
• The naturally occurring cases studied were adult horses of various breeds that were housed in a Virginia boarding stable. For experimental comparison, two healthy adult horses and two healthy adult sheep were used in feeding trials.
• To understand the impact of the disease, blood and liver specimens from the affected animals were collected for analysis during the outbreak. Treatments given included primarily supportive care along with the critical intervention of hay withdrawal.

Results of the Study

• The severity of hepatotoxicosis caused by Panicum hay was evidenced in the fact that five affected animals had to be euthanized. However, the majority of affected horses, including those used in the research trials, recovered once the hay was removed from their diets.
• Through bloodwork and liver specimens, all affected animals showed signs of hepatic disease illustrated by abnormal levels of key liver enzymes like aspartate aminotransferase (AST), sorbitol dehydrogenase (SDH), gamma glutamyl transferase (GGT), and alkaline phosphatase (ALP).
• Examination of liver biopsy specimens further revealed inflammation and signs of cell damage including prominently clumped chromatin, signs of hydropic degeneration, and necrosis of individual liver cells.

Conclusion

• Exposure to hay made from Panicum dichotomiflorum leads to rapid development of severe hepatotoxicosis in horses. Horses that consumed this contaminated hay suffered from patchy hepatocyte necrosis, implicating apoptosis, a type of programmed cell death, as the mechanism of hepatotoxicosis.
• The study reveals that omission of Panicum hay should allow all but the most severely affected animals to recover from acute exposure, considering there was no fibrosis or irreversible liver tissue scarring seen in research animals.