Resolution of neurologic signs presumed to be associated with hyperammonemia in 2 endurance horses

This case report describes 2 endurance horses with non-hepatic hyperammonemia. The animals were competing in a 160-km endurance competition in extreme heat conditions and were presented for obtundation. One of the horses also had evidence of blindness. The blood ammonia concentration was elevated (196 μmol/L and 249 μmol/L) and both horses improved following treatment with intravenous fluids and supportive care. These are the first documented cases of clinical signs presumed to be associated with hyperammonemia in endurance horses. Despite the severity of the clinical presentation, both horses made a full recovery. Key clinical message: Non-hepatic hyperammonemia should be considered as a potential cause of blindness and obtundation in competing endurance horses. Horses appear to respond well to treatment with intravenous fluids.