Serum hepatitis in two brood mares.

Two adult Quarter Horse mares from the same farm developed signs of hepatic disease approximately 2 months after parturition. Both mares had received tetanus antitoxin at the time of foaling. One mare developed subcutaneous edema of the distal aspect of all 4 limbs, photodermatitis involving unpigmented areas of skin, and high serum activities of liver-specific enzymes. The other mare had signs of acute hepatic failure, including icterus, hepatic encephalopathy, and high serum activities of liver-specific enzymes, and died. The second mare had signs typical of serum hepatitis (Theiler's disease) and the first mare was believed to have had an atypical, less-severe form of serum hepatitis. Hepatotoxic agents (eg, poisonous plants, aflatoxins, toxic chemicals) were not found on the farm.