The above examples of homologous transfer of passive immunity set the stage for considering the opportunities for heterologous passive transfer. Immune milk products generally are some form of protein product derived from the colostrum and/or milk of dairy cattle. The cows typically are hyperimmunized against one or more antigens representing pathogens of bacterial or viral origin. Crude preparations of the immunoglobulin from colostrum or milk may range from essentially no alteration of the immunoglobulin concentration in the product to partial immunoglobulin isolation or concentration in a whey protein concentrate.