What Is Colostrum?
Colostrum is the first milk produced by the mammary glands, secreted from approximately 16 weeks of pregnancy and present in the breast at birth. It is produced in small quantities — typically 40–50ml total per day in the first 1–3 days — but its concentration of bioactive compounds per millilitre is extraordinary. It transitions to transitional milk (days 5–14) and then mature milk (from approximately 2 weeks postpartum) as volume increases and composition shifts.
Immunological Content
Colostrum's most remarkable property is its immunological richness. It contains approximately 2–5g of secretory IgA (sIgA) per litre — 10–100 times higher than mature milk. This sIgA coats the intestinal mucosa of the newborn, providing passive immune protection while the infant's own immune system develops. Colostrum also contains high concentrations of lactoferrin (an antimicrobial protein), lysozyme, and various cytokines and growth factors. Maternal antibodies to pathogens the mother has encountered (through infection or vaccination) are transferred via colostrum.
Nutritional Composition
Colostrum differs from mature milk in composition: it is lower in fat and lactose, higher in protein (particularly immunoglobulins and growth factors), and higher in some minerals (zinc, sodium, chloride) than mature milk. Its slightly laxative effect facilitates the passage of meconium (the infant's first stool) and bilirubin excretion, reducing jaundice risk. Its low volume matches the newborn's tiny stomach capacity.
Pre-birth Expression
Some pregnant people hand-express colostrum from 36 weeks of pregnancy (antenatal colostrum expression) to store for use in the early postpartum period, particularly if there are concerns about breastfeeding challenges. This practice is supported for low-risk pregnancies by some midwifery guidelines; it is generally avoided in pregnancies with preterm birth risk due to the nipple stimulation effect.
