They lack hundreds of enzymes, hormones, anti-infectives, and living cells that are found in breastmilk. Nursing is a lifelong baby gift that only Mom can give. Bottle-feeding mothers have added health risks. Without her normal nursing hormones, a bottle-feeding mother's body recovers from birth more slowly, and her risk of certain breast and ovarian cancers rises. She also loses out on the relaxing, patience- producing effects of nursing hormones at a time when life can be especially stressful.
Breastfed babies have a head start.
Nursing for even a few days gives a baby the food and snuggling for which he is designed. It makes sense.