Role of milk immunoglobulins in the Brucella milk ring test.

Milk immunoglobulins were extracted from the stained cream layer of positive milk ring tests from experimentally inoculated or naturally infected cows. IgA was always found, associated with IgM in most cases (15/17) and with IgG in a smaller number of cases (11/17). An additional incubation at 20 degrees C for 18 h gave clearer positive and negative results and a lower limit of detection than that of the usual milk ring test.