A study of the macro and micro immunoglobulins to Brucella abortus and their transfer from cow to calf via the colostrum.

Samples of adult bovine serum, colostrum, the serum of unsuckled and suckled calves were subjected to gel filtration through Sephadex G 200. All samples (except those of unsuckled calves) contained antibodies to Brucella abortus. Four phases were recorded in normal adult serum corresponding to IgM, IgG, Albumin and a fourth phase of smaller nitrogen-containing molecules. In colostrum phase 2 was relatively large and phase 3 was absent indicating absence of albumin. In the serum of the unsuckled calves phase 2 was absent, indicating a virtual absence of IgG. Agglutinins and Complement fixing antibodies were found in the fractions of both phase 1 and phase 2. Incomplete antibodies occurred only in phase 2, which suggested that they occurred only as 7S molecules. By immunising pregnant heifers shortly before calving with formalin Killed Strain 19 vaccine, it was found that serum IgM may be secreted in colostrum and in this manner transferred to the calf on suckling. It is considered that the immunoglobulins of importance in protecting the young calf from Br. abortus, and also in neutralising Strain 19 vaccination, are of the IgG incomplete (7S) class. These antibodies appear to be less heat-labile than 7S agglutinins.