ABSTRACT
This chapter reviews systems that function in extraintestinal tissues in transmitting antibody and other macromolecules from mother to young. The bulk of the relevant information is derived from investigations carried out in cow udder, rabbit visceral yolk sac and human placenta. In the sow the major part of colostral IgA is synthesized in the mammary gland, and the rest is secreted from the serum. The secretory mechanism may have much in common with the mechanism known in the gut and in the respiratory tract. The source of colostral IgG and most of the colostral IgM is the serum, while the immunoglobulins of the mature milk are produced mainly in the mammary gland. The appearance of IgG1 receptors and the onset of colostrum secretion requires a high initial progesterone level and increasing estrogen and decreasing progesterone concentrations. All the requirements are met in the preparturition weeks in the cow.
