Gilbert syndrome is a congenital hyperbilirubinemia that occurs in humans (inherited as an autosomal dominant trait) and in Southdown sheep. It is an unconjugated hyperbilirubinemia not caused by inappropriate hemolysis; a defect in carrier proteins or conjugating enzyme is suspected. Affected Southdown sheep have increased conjugated and unconjugated plasma bilirubin concentrations; hepatic bilirubin clearance is defective. Icterus varies. Histopathologic lesions are absent except for pigment in the hepatocytes.
Dubin-Johnson syndrome—a failure of conjugated bilirubin to enter the bile canaliculi—occurs sporadically in humans and in Corriedale sheep. Excretion of bilirubin and other conjugated organic anions may be impaired. Affected sheep may be icteric or hyperbilirubinemic. Serum concentrations of conjugated and unconjugated bilirubin are increased, and bile acid excretion may be delayed. Histologically, the hepatocytes contain a black, melanin-like pigment.