Pathogenesis of the downer cow syndrome.

A historical review of the downer cow literature is presented in order to provide a background for understanding current research. Initially thought to be an entity separate from parturient paresis, the condition has eventually come to be regarded as a complication of parturient paresis. Since many other factors also contribute to the syndrome, it is difficult to define precisely what is meant by the term 'downer cow'. A hypothesis that many primary factors, including parturient paresis, may cause the initial stage of recumbency is presented. This is followed by secondary muscle and nerve damage caused by tissue compression. This damage leads to permanent recumbency even if the primary factors have been ameliorated by therapeutic measures. Support for this hypothesis is given from the literature on cattle and other species and from recent experiments on cows. The concepts are applied to a discussion of prevention and therapy of downer cow cases.