Commonly referred to as "baby's first milk," colostrum is the leftover mixture of materials present in the mammmary gland and ducts at delivery. It slowly becomes mixed with newly secreted milk, yet it differs from mature milk in composition and is not as plentiful.
One of the major purposes of colostrum is to aid in the formation of the "good" bacteria, or Bifidus flora, in the GI tract. It also eases the movement of meconium. Colostrum is abundant in antibodies to protect the baby against bacteria and viruses in the birth canal and from human contact.