Final answer:
Secretory Immunoglobulin A (IgA) is the primary antibody present in breast milk, which provides infants with passive immunity against pathogens by binding and neutralizing them. This form of immunity is part of the natural protection infants receive from their mothers after birth.
Step-by-step explanation:
The antibody present in breast milk is Secretory Immunoglobulin A (IgA). Upon the birth of a child, antibodies produced in the mother's body are passed to the infant via passive immunity through breast milk. This transfer of immunity is a crucial part of the infant's early immune defense.
Secretory IgA in the milk provides protection by binding and neutralizing pathogens, thus defending the baby against bacterial and viral infections. In addition, passive immunity can also occur through the placenta with the transfer of IgG antibodies from mother to infant, lasting up to six months after birth.