A case of intestinal hyperammonemia secondary to Salmonellosis in a 7-year-old Arabian gelding

Hyperammonaemia (HA) in horses is most commonly associated with hepatic dysfunction and hepatic encephalopathy; however, it may also occur secondary to acute gastrointestinal disease in the absence of primary hepatic pathology. Intestinal hyperammonaemia is thought to result from increased intestinal production and absorption of ammonium due to dysbiosis, mucosal compromise and intestinal inflammation. This report describes a case of intestinal hyperammonaemia–associated encephalopathy secondary to culture-confirmed salmonellosis in an adult horse, with survival and full clinical recovery. A 7-year-old Arabian gelding was referred for evaluation of colic and pyrexia. Clinical findings were consistent with systemic inflammatory response syndrome, accompanied by multifocal neurological abnormalities including altered mentation and ataxia. Clinicopathological findings included leukopenia, neutropenia, hyperbilirubinaemia and marked hyperammonaemia. Serum hepatic enzyme activities, bile acid concentrations and diagnostic imaging were not supportive of primary hepatic disease. Faecal culture identified Salmonella enterica serotype Typhimurium, confirming salmonellosis-associated colitis. In the absence of hepatic dysfunction, intestinal hyperammonaemia was considered the most likely cause of the observed neurological signs. Treatment focused on management of colitis and endotoxaemia, alongside intensive supportive care, including lactulose administration to reduce serum ammonia concentrations. Serial monitoring demonstrated rapid normalisation of ammonia levels concurrent with resolution of neurological signs. The horse survived to discharge and returned to its intended use, with no recurrence of neurological abnormalities. This case highlights intestinal hyperammonaemia as an important differential diagnosis in horses with colitis and acute neurological signs and demonstrates the potential for favourable outcomes with prompt recognition and aggressive management.