Breastmilk like all the other mammalian milks is species specific. It is uniquely designed for that one particular species.
In the past 2-3 decades there has been a push in the United States and the UK for babies to get only breastmilk for at least the first 6 months of life. Why is this? It is because breastmilk is a living food. It is full of antibodies and other components that helps support and protect the infant. If you want to understand the role of breastfeeding, you must first understand how the world of microbes affects the new born baby.
At delivery, the sterile baby is thrust into a world full of bacteria. Babies are born with very tiny immune systems. Every time the baby comes into contact with bacteria, the baby's immune system responds to this. During pregnancy the placenta protects the baby. After delivery mother's milk takes the place of the placenta. It takes a long time before the baby is able to fully defend itself.
Most infections reach the baby through the mucous membranes of the respiratory and intestinal tracts. Only mother's milk provides the protection necessary to defend those areas. Babies that do not receive mother's milk must use their own energy to fight off the infection. Infection in these babies causes tissue damage and loss of energy. This puts the baby at risk of ear infections, upper respiratory infections, diarrheal infections, celiac's disease and more. The protection afforded by the mother's milk protects against certain infections, improves the baby's response to vaccinations, possibly protects against obesity and prevents celiac's disease. This protection is duration related and lasts long after breastfeeding has stopped.
Scientists have been studying human milk and its complexity over the last several decades. The understanding of the immunology of breastmilk is growing rapidly. What we know is that every ounce of breastmilk you give your baby is an ounce of prevention, but in order for the baby to be optimally protected she needs her own mother's milk (or donor milk if mother's milk is not available) exclusively for at least 6 months. Continuing to breastfeed for at least a year will be the most important gift you give to your child.
Breastfeeding-for the babies' sake