Hepatic disease in Alberta horses: A retrospective study of 'alsike clover poisoning' (1973-1988).

Over sixteen years, 49 horses were diagnosed by Alberta Agriculture Animal Health laboratories as having "alsike clover poisoning". There was a distinct northwestern distribution of cases, the majority coming from the Peace River district. This distribution is opposite to that of the Alberta horse population, but coincides with areas of alsike clover cultivation. Cases could be divided into chronic or nervous clinical presentations, as described by Schofield. Tissues from 45 animals were retrieved and examined microscopically. Significant histological lesions were confined to the liver and consisted of biliary fibrosis and epithelial proliferation.I conclude that alsike clover poisoning is a specific disease entity, likely due to exposure to an exogenous toxin. The evidence is not strong enough to incriminate alsike clover as the etiology.