Colostrum is a sticky, thick, yellowish liquid produced by a woman's breasts toward the end of pregnancy and during the first few days after delivery of her baby. Colostrum contains protein, minerals, and vitamins as well as valuable antibodies, which help protect the baby against disease.

Women who breastfeed transfer these important nutrients to their newborns. Colostrum is particularly suited to a newborn's needs and provides the ideal nutrition. Its yellow tint comes from higher levels of carotene, a form of vitamin A. Colostrum also may act as a laxative to help the infant pass the first few bowel movements, which are a dark green substance called meconium.

After a few days, a woman's breasts start supplying the baby with transitional milk as breastfeeding becomes established, followed by mature milk at about 10 to 15 days after delivery.