Overview
The equine liver (hepar) rests on the abdominal surface of the diaphragm, in the intrathoracic part of the abdomen, and is covered by the ribs on both sides. In the foal it is almost symmetrical; in the adult most of it lies on the right, and in older horses the right lobe often atrophies, probably from pressure by the base of the caecum and the right dorsal colon. Its visceral surface touches the stomach, the duodenum, the right dorsal colon, the base of the caecum and the right kidney.
Lobes and vessels
- Lobes: the fissures are deeper than in cattle. There is a left lobe divided into lateral and medial parts, a quadrate lobe, a right lobe and a caudate lobe with a marked caudate process; there is no papillary process.
- Caudal vena cava: runs along the dorsal border before passing through the diaphragm.
- Hilus (porta hepatis): the portal vein and hepatic artery enter and the hepatic duct leaves here.
Bile ducts
- No gallbladder: the horse has no vesica fellea; bile is secreted continuously, matching an almost constant food intake.
- Bile duct: formed by the union of the hepatic ducts, it opens together with the pancreatic duct on the major duodenal papilla in the duodenal ampulla.
Clinical relevance
- Pyrrolizidine alkaloid poisoning: prolonged intake of plants such as ragwort (Jacobaea vulgaris) causes progressive liver fibrosis with megalocytosis, photosensitisation and hepatic encephalopathy, often months later.
- Serum hepatitis (Theiler's disease): acute hepatic necrosis in adult horses weeks after receiving biological products of equine origin, such as tetanus antitoxin.
- Hyperlipaemia: in obese ponies, donkeys and miniature horses in negative energy balance (pregnancy, illness, fasting), mobilised fat infiltrates the liver; mortality is high.
- Cholelithiasis: stones in the bile ducts causing intermittent colic, fever and jaundice.
- Examination: the liver cannot be palpated; it is examined by ultrasound through the caudal right intercostal spaces, where guided biopsy is also taken.