Milk is a maternal lactating secretion, a short term nutrient for new-borns.
Nothing more, nothing less. Invariably, the mother of any mammal will provide her milk for a short period of time immediately after birth. A familiar example is that of a puppy. The mother nurses the pup for just a few weeks and then rejects the young animal and teaches it to eat solid food. Nursing is provided by nature only for the very youngest of mammals.