Colostrum is a thick white/yellow substance produced by the breasts. It is commonly called the first milk. Most women do not notice it until after the birth, although it starts being produced from as early as 20 weeks in pregnancy. Although it is not produced in abundance, it is concentrated with lots of nutrients; It is high in Protein and vitamin K. it also contains antibodies and white blood cells to protect babies against infection. The Colostrum helps your baby to excrete waste products and will line the stomach with a protective layer that helps fight against foreign substances in the body. It is thought that Colostrum helps to prevent allergies.
Ref; Expecting everything you need to know about pregnancy labour and birth 2004.
McGrail A, Metland D
MIDIRS Informed choice leaflet; No.7 breastfeeding or bottle feeding