Colostrum (also known as beestings or first milk) is a form of milk produced by the mammary glands in late pregnancy and the few days after giving birth.

Human and bovine colostrum is thick and yellowish. In humans, it has high concentrations of nutrients and immunities, but it is small in quantity.

Colostrum is high in carbohydrates, protein and antibodies, and low in fat, which human newborns may find difficult to digest. Newborns have very small digestive systems, and colostrum delivers its nutrients in a very concentrated low-volume form. It has a mild laxative effect, encouraging the passing of the baby's first stool, which is called meconium. This clears excess bilirubin, a waste product of dead red blood cells which is produced in large quantities at birth due to blood volume reduction, from the infant's body and helps prevent jaundice.

Colostrum contains large numbers of antibodies called "secretory immunoglobulin" (IgA) that help protect the mucous membranes in the throat, lungs, and intestines of the infant. Leukocytes are also present in large numbers; these begin protecting the infant from harmful viruses and bacteria. Ingesting colustrum establishes beneficial bacteria in the digestive tract.

Premature babies tend to fare better on human colostrum than manufacured baby milks. Human milk contains special components, called growth modulators, that help the premature baby's digestive system adjust to oral feedings (Davies 1989). Research (Schlanler 1999b; Gross and Slagle 1993; Lucas 1987; Lucas 1984) indicate that premature babies fed formula tend to vomit more and continue tube feeding longer than those fed human colostrum and breast milk.

Bovine colostrum is sometimes used by humans as a dietary supplement. It has been attributed with curative powers and used as an ingredient in food dishes for the ill or invalid (Davidson, 1999)