Source Naturals, Colostrum, 4 ozProduct Description Colostrum is the first milk given to a newborn calf by its mother, and contains proteins including immunoglobulins, or antibodies, that may not be present in ordinary milk. Colostrum is normally secreted only in the first 48 to 72 hours after birth. Source Naturals Colostrum is true bovine colostrum (not cheese whey), collected within the first 12 hours of production. It is then standardized, so that the immunoglobulin proteins