The function of these immunoglobulins (antibodies) is as follows:

•IgG — predominant immunoglobulin in bovine milk colostrum; primary function is to identify and help destroy invading pathogenic microbes.

•IgA — predominant immunoglobulin in human milk and colostrum; primary role is as first line of defense, protects mucosal surfaces and prevents the attachment of pathogens to them.

•IgM — primary role is "first to fight;" enhances phagocytosis by destroying invading pathogens.

•IgE — involved with the allergic reaction and histamine-associated allergic reaction; also involved with active defense against enteric parasites.

•IgD — attached to B cells; it stimulates lymphocytes to produce antibodies by presenting antigens to them