Mother’s milk is considered very essential for the newborn infant.
The yellowish watery milk colostrum secreted by mother during the initial days of lactation has abundant antibodies (IgG and IgA) to protect the infant. Colostrum is rich in proteins and antibodies and protects the newborn until its own immune system matures. Colostrum is the first substance secreted by the mammary glands shortly before and after delivery (appears for two or three days after delivery).
This is an example of passive immunity.