The nature of the local immune system of the bovine mammary gland.

The origin of the immunoglobulins of bovine colostrum and milk were examined by using radiolabeled protein. Colostrum was found to consist mainly of immunoglobulin derived from serum, although there was some local synthesis. In lactation the immunoglobulins of milk were almost entirely serum derived. The local immune system was very inactive but could be stimulated to activity by local immunization. The immunoglobulin profiles of the secretion from the stimulated gland were still relatively deficient in IgA compared to other species, notably the pig.