colostrum

colostrum, viscous, yellow-colored fluid produced by the mammary glands of humans and other mammals during the first few days after giving birth, before the onset of mature breast milk. The composition of colostrum, particularly its immune components, varies across species, mainly because of differences in placental structure.

In humans colostrum production in the mammary glands starts between the 12th and 18th week of pregnancy and is the only milk released for the first few days after giving birth. Colostrum begins to be replaced by transitional milk, which is thinner and especially rich in fat, within two to five days after birth. After about two weeks, it is fully replaced by mature breast milk, which consists mainly of water, with small amounts of carbohydrates, fats, and proteins; this milk is essential for infant hydration and continued growth.

The concentrated formulation of nutrients and immune factors in colostrum provides newborns with a complete diet and immunity, supporting their growth and helping to defend against infections immediately after birth. In particular, colostrum contains high amounts of proteins, especially antibodies. Once ingested and in the gastrointestinal tract, some of these antibodies coat the intestinal lining, protecting the newborn from harmful bacteria and other agents that may have entered the body during the birthing process, while others are absorbed into the bloodstream, where they provide systemic immunity. Colostrum is also abundant in various minerals, vitamins, and growth factors and has laxative effects, promoting the first bowel movement (meconium), which in turn helps to clear bilirubin and reduce the risk of jaundice.

Owing to its rich nutritional and immune properties, bovine colostrum (from cows) is processed into powdered form and sold as a dietary supplement.