Hepatic Encephalopathy in a Connemara Pony

A 3-year-old female Connemara pony was referred to Jeju National University Equine Hospital because of weight loss and prolonged anorexia. On admission, heart and respiratory rates were slightly elevated while body temperature was within the normal range. The color of the conjunctival and oral mucosa was yellowish pink. The blood chemistry results showed that total bilirubin, aspartate aminotransferase, and gamma-glutamyl transferase levels were remarkably elevated while blood urea nitrogen was within the reference range. Transcutaneous abdominal ultrasound revealed an enlarged right lobe of the liver with prominently increased parenchymal echogenicity, reduced hepatic vessels, and rounded caudal border. The pony was tentatively diagnosed with chronic hepatitis and icterus; rest and supportive treatments were provided. Clinical signs aggravated on day 2 with hind quarter paresis and cranial nerve signs such as circling, drooping, jerking, and head pressing against walls. Recumbency and generalized ataxia (grade 5/5) were shown on day 3. Plasma ammonia concentration on day 3 was as high as 656 µmol/L. Necropsy and histopathologic examinations strongly supported a diagnosis of hepatic encephalopathy. This case of hepatic encephalopathy exhibited rapid progress from low to terminal grade within 4 days in a Connemara pony. The results provide well-established clinical and pathological data for future application.