ABSTRACT
In ponies and miniature horses, the most common cause of acute hepatic disease and failure is hepatic lipidosis, whereas in adult horses, the most common syndromes causing both hepatic disease and failure are Theiler’s disease and pyrrolizidine alkaloid toxicosis. In foals, important causes of liver disease include Tyzzer’s disease, toxic hepatopathies (such as iron fumarate toxicity), hepatitis secondary to septicemia, and equine herpesvirus-1. Moderate elevations in serum gamma glutamyl transferase (GGT) can be seen in foals with significant gastroduodenal ulceration, especially pyloric outflow obstruction and stricture formation.2 This may be due to restricted bile outflow through the sphincter of Oddi, or bile stasis and incomplete intrahepatic biliary clearance resulting from abnormal intestinal motility. A similar elevation in serum GGT (unaccompanied by other biochemical evidence of liver disease) occurs in mature horses with protracted enteritis, or postoperative ileus.2 Elevated
Liver disease is common in the horse, and a great many disorders can cause hepatic disease (i.e., pathologic change or damage to the liver) in both adult horses and foals. Few of these diseases, however, result in hepatic failure. The liver carries an immense reserve capacity (approximately 80%), and liver damage, therefore, must be advanced before physiologic failure occurs.1 For example, horses with strangulating or inflammatory intestinal diseases frequently have evidence of liver disease (elevated hepatic enzymes in the serum) caused by portal hypoxia and/or increased concentrations of endotoxin in the portal circulation, but these conditions rarely progress to liver failure. The distinction between hepatic disease and hepatic failure is clinically important. In view of the large reserve capacity, many horses with mild hepatic disease will make a full recovery given time and removal of the inciting cause, provided that the diagnosis is made relatively early. If the damage progresses to cause liver failure, however, the prognosis for survival is markedly decreased.2,3,4
Hepatic failure is a serious condition that requires intensive therapy. If the diseased liver is capable of repair and regeneration, recovery is possible; but if the damage is irreversible (e.g., associated with severe fibrosis or cirrhosis) (Figure 11-1), death will ensue. Rarely can the diagnosis of liver disease be made purely on the results of a clinical examination, unless there is fulminant hepatic failure (as evidenced by encephalopathy and jaundice).
