Colostrum (occasionally known as "beestings") is a form of milk produced by the mammary glands in late pregnancy and the first hours after giving birth.

Human and bovine colostrum is thick and yellowish. It 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, called meconium. This clears excess bilirubin 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, that begin protecting the infant from harmful viruses and bacteria. Ingesting colustrum establishes beneficial bacteria in the digestive tract.

Bovine colostrum is sometimes used by humans as a dietary supplement.