Colostrum is the first milk produced by the mammary glands immediately after childbirth. It is rich in antibodies, particularly Immunoglobulin A (IgA), which provides passive immunity to the newborn by protecting mucous membranes against pathogens. This early milk also contains high concentrations of proteins, vitamins, and minerals crucial for the baby's initial growth and immune defense. Unlike mature milk, colostrum is produced in small quantities but is highly concentrated, making it essential for neonatal health and infection prevention.

Reference: Nelson Textbook of Pediatrics, Kliegman RM, 21st Edition.