When kittens are born, their immune systems are not fully developed and they are at risk of infections. They do, however, receive help from their mother’s milk, specifically the first milk she produces after the kittens are born.
This thick yellowy milk (colostrum) is made for only about 72 hours after birth and is rich in external antibodies that protect the kittens against infections to which the mother is already immune. This protection lasts for 8–10 weeks, by which time kittens are able to make their own antibodies.
Recent research has shown that receiving colostrum is crucial in the first 18 hours of a kitten’s life. During that time, the antibodies cross the wall of the kitten’s intestine and are absorbed into the bloodstream. Thereafter, the kitten’s body loses the ability to absorb antibodies passed on from the mother cat.