Hepar
The equine liver weighs roughly 5 kg (about 1% of body weight) and lies primarily on the right side of the abdomen against the diaphragm. Unlike many species, the horse has no gallbladder. Bile is produced continuously by the hepatocytes and drains directly into the duodenum via the hepatic and common bile ducts. The liver performs many functions, including bile production for fat digestion, protein synthesis (including clotting factors), glycogen storage, detoxification, and bilirubin metabolism. It receives dual blood supply from the hepatic artery and the portal vein (nutrient-rich blood from the gut). It has remarkable regenerative capacity. Clinical signs of liver failure may not appear until a large portion of function is lost.
Liver enzymes (GGT, SDH, AST, ALP) and bile acids are key diagnostic markers. Ultrasound can assess size and echogenicity. Liver disease is less common than gastrointestinal problems but can be serious. Choleliths can occasionally occur even without a gallbladder.
## Overview Hepatic lipidosis is fatty infiltration of the liver that occurs with hyperlipemia, most often in ponies, miniature horses, and donkeys under negative energy balance. It causes depression
Chronic liver damage caused by ingestion of plants containing pyrrolizidine alkaloids (e.g., Senecio spp., Crotalaria, Echium). Megalocytosis and biliary fibrosis are characteristic histopathological
## Overview Theiler’s disease is acute hepatic necrosis, one of the most common causes of acute liver failure in adult horses. It is associated with administration of equine-origin biological product
## Overview Cholangiohepatitis is inflammation of the bile ducts and adjacent liver tissue, usually from ascending bacterial infection. It is one of the more common liver diseases in adult horses and
## Overview A liver abscess is a focal pocket of bacterial infection within the liver. It is uncommon in horses. Clinical signs are often vague: intermittent fever, weight loss, mild colic, and eleva
## Overview Cholelithiasis is the formation of stones (usually calcium bilirubinate) within the biliary tree of the horse. Stones may be incidental or may obstruct bile flow, producing cholangiohepat
## Overview Tyzzer’s disease is an acute, highly fatal hepatitis of foals 1 to 6 weeks old (most often 7 to 42 days) caused by Clostridium piliforme. Foals are infected by ingesting spores from conta
Jaundice, unexplained weight loss, or neurologic signs (hepatic encephalopathy) should be evaluated promptly. The liver is not something owners manage directly day to day.
## Overview Hepatic lipidosis is fatty infiltration of the liver that occurs with hyperlipemia, most often in ponies, miniature horses, and donkeys under negative energy balance. It causes depression, inappetence, weight loss, and elevated liver enzymes. The condition can progress to liver failure. ## Causes Negative energy balance (anorexia, pregnancy, lactation, stress, or concurrent disease) triggering massive fat mobilization. ## Diagnosis Clinical signs plus markedly elevated serum triglycerides and liver enzymes. Ultrasound may show a hyperechoic liver. ## Treatment Aggressive nutritional support to reverse negative energy balance, treatment of any primary disease, and supportive care. Insulin or heparin is sometimes used. ## Recovery and Prognosis Guarded, especially in ponies and miniatures. Early intervention improves survival. ## Prevention Avoid prolonged anorexia in at-risk equids. Maintain body condition carefully. Signs include: inappetence; weight loss; jaundice; depression; elevated liver enzymes and triglycerides
Chronic liver damage caused by ingestion of plants containing pyrrolizidine alkaloids (e.g., Senecio spp., Crotalaria, Echium). Megalocytosis and biliary fibrosis are characteristic histopathological findings. Signs include: Weight loss; jaundice; photosensitization; neurological signs (hepatic encephalopathy); often fatal; photosensitization (unpigmented skin); icterus; hepatic encephalopathy (head pressing, aimless wandering, yawning); diarrhea
## Overview Theiler’s disease is acute hepatic necrosis, one of the most common causes of acute liver failure in adult horses. It is associated with administration of equine-origin biological products (antitoxin, plasma, serum) and typically appears 4 to 10 weeks later. A pegivirus has been implicated. Signs include acute depression, jaundice, and hepatic encephalopathy with head pressing. Mortality in clinical cases is high (50 to 90 percent). ## Causes Viral hepatitis, often linked to equine-origin biologics. ## Diagnosis History of recent biologic administration, elevated liver enzymes, jaundice, and clinical signs of liver failure. ## Treatment Supportive care only. No specific antiviral therapy. Prognosis is poor once encephalopathy develops. ## Recovery and Prognosis Poor for clinical cases. Horses that survive the acute phase may recover. ## Prevention Judicious use of equine-origin biologics. Modern products have reduced risk. Signs include: acute depression; jaundice; hepatic encephalopathy; head pressing; high mortality; often 4 to 10 weeks after equine biologic
## Overview Cholangiohepatitis is inflammation of the bile ducts and adjacent liver tissue, usually from ascending bacterial infection. It is one of the more common liver diseases in adult horses and is frequently associated with choleliths. Classic signs are fever, colic, and jaundice. ## Causes Ascending enteric bacteria (often Gram-negative or anaerobic) secondary to biliary stasis. Cholelithiasis is a frequent concurrent finding. ## Diagnosis Clinical signs plus elevated liver enzymes, ultrasound evidence of dilated ducts or choleliths, and liver biopsy for histopathology and culture. ## Treatment Prolonged antimicrobial therapy guided by culture when possible, supportive care, and, when indicated, surgical or endoscopic management of obstructing stones. Treatment often continues for many weeks until enzymes normalize. ## Recovery and Prognosis Fair if treated early and fibrosis is limited. Presence of hepatic encephalopathy or severe fibrosis worsens the outlook. Recurrence is possible. ## Prevention No specific prevention. Prompt treatment of biliary disease may limit progression. Signs include: fever; intermittent colic; jaundice; depression; weight loss; elevated liver enzymes
## Overview A liver abscess is a focal pocket of bacterial infection within the liver. It is uncommon in horses. Clinical signs are often vague: intermittent fever, weight loss, mild colic, and elevated fibrinogen. Ultrasound detects the cavitary lesion, and aspiration confirms pus. ## Causes Bacterial seeding, sometimes from the gut or via the portal circulation. Specific organisms vary. ## Diagnosis Ultrasound showing a fluid-filled lesion in the liver, aspiration of purulent material, and culture. ## Treatment Long-term antibiotics based on culture, and surgical or percutaneous drainage when feasible. Prognosis is guarded. ## Recovery and Prognosis Guarded. Published survival is limited. Early drainage improves the chance. ## Prevention None specific. Signs include: intermittent fever; weight loss; colic; elevated fibrinogen; cavitary lesion on ultrasound
## Overview Cholelithiasis is the formation of stones (usually calcium bilirubinate) within the biliary tree of the horse. Stones may be incidental or may obstruct bile flow, producing cholangiohepatitis, colic, fever, and jaundice. Middle-aged horses are most often affected. ## Causes The exact cause is unknown. Biliary stasis, ascending infection, and changes in bile composition are proposed. Foreign material or parasites can act as a nidus. ## Diagnosis Ultrasound frequently visualizes the stones and dilated ducts. Clinical pathology shows biliary stasis. Biopsy and culture evaluate concurrent cholangiohepatitis. ## Treatment Antimicrobials for associated infection, and surgical or lithotripsy removal of obstructing stones when feasible. Prognosis depends on the degree of liver damage. ## Recovery and Prognosis Guarded when obstruction and significant hepatitis are present. Incidental stones found without clinical signs may require only monitoring. ## Prevention None specific. Signs include: intermittent colic; fever; jaundice; weight loss; depression; ultrasound evidence of biliary stones
## Overview Tyzzer’s disease is an acute, highly fatal hepatitis of foals 1 to 6 weeks old (most often 7 to 42 days) caused by Clostridium piliforme. Foals are infected by ingesting spores from contaminated feces or the environment. Signs include peracute death, profound depression, fever, jaundice, diarrhea, and convulsions. Even with aggressive treatment, virtually all affected foals die within about 35 hours of onset. ## Causes Clostridium piliforme infection. ## Diagnosis Clinical signs in a young foal, liver enzyme elevation, and post-mortem confirmation of hepatic necrosis with intracellular bacteria. ## Treatment Intensive supportive care and antibiotics. Success is extremely rare. ## Recovery and Prognosis Grave. Nearly all foals die. ## Prevention Good hygiene to reduce fecal contamination. No vaccine is available. Signs include: peracute death in foals; profound depression; fever; jaundice; diarrhea; convulsions
Liver enzymes (GGT, SDH, AST, ALP) and bile acids are key diagnostic markers. Ultrasound can assess size and echogenicity. Liver disease is less common than gastrointestinal problems but can be serious. Choleliths can occasionally occur even without a gallbladder.
Jaundice, unexplained weight loss, or neurologic signs (hepatic encephalopathy) should be evaluated promptly. The liver is not something owners manage directly day to day.
See the Liver on our interactive 3D horse model. Open 3D Model