Colostrum is a unique milk fluid produced in late pregnancy and fed to babies after birth. It's thicker and more yellow than mature milk, and often referred to as 'liquid gold'.
Colostrum is produced at low volumes for little tummies, and because it's so dense with nutrients and immune factors, a little goes a long way.
Colostrum is replaced by mature milk 2-8 days following birth, when the mother's mature milk 'comes in'.
Colostrum is a living fluid, full of immune and growth related cells. The white blood cells (or leukocytes) in colostrum directly fight infection and activate defence mechanisms in the immune system.
Colostrum is lower in lactose, potassium, calcium and some vitamins than mature milk, suggesting that its primary role is immunological rather than nutritional.
Breast milk continues to change in amazing, adaptive ways beyond this transition - within feeds, over the 24hr circadian cycle and over months and years of nursing. Scientists are only beginning to unveil the significance of some of these changes, in not just building immunity, but establishing the microbiome and more.
Wambach, K. R. J. (2016). Breastfeeding and Human Lactation. Burlington: Jones & Bartlett Publishers.