Diarrhea and hyperammonemia in a horse with progressive neurologic signs

A 2-year-old, Quarter Horse filly was referred to Michigan State University, Veterinary Teaching Hospital with a 2-3 day history of depression and partial anorexia progressing to severe, watery diarrhea with severe neurologic abnormalities, including repetitive muscle fasciculations, muscle stiffening, and collapse. Laboratory findings included severe polycythemia, neutropenia, metabolic acidosis, and electrolyte and fluid loss, consistent with watery diarrhea and endotoxic shock. Increased creatine kinase and aspartate transaminase activities were consistent with recent transport and the muscle abnormalities. Severe hyperammonemia (1369.0 micromol/L; control value, 15.3 micromol/L) was found, without other substantial laboratory evidence of hepatic dysfunction. The horse was euthanized because of poor prognosis and rapid clinical deterioration. Necropsy findings were unremarkable with the exception of severe diffuse colitis. Culture of colonic contents recovered >1000 colony-forming units of Clostridium perfringens. Based on these findings, marked hyperammonemia in this filly was attributed to changes in colonic flora leading to increased bacterial production of ammonia that was readily absorbed through the inflamed bowel wall, exceeding the hepatic capacity for deamination. Intestinal bacteria as a source of hyperammonemia in the absence of hepatic disease has been linked rarely to positive culture results for clostridial organisms.