Whose discovery explained that mammalian milk is an ideal food because it contains antibodies and nutrients tailored for infants?

The idea that mammalian milk is more than simple nourishment developed gradually through physiology and immunology research. Scientists learned that milk contains fats, proteins, sugars, minerals, immune factors, and hormones that support growth and protection. Colostrum, the first milk after birth, is especially rich in antibodies such as immunoglobulin A. This helped explain why mammalian mothers provide more than calories to their young.