The benefits of mother's milk have long been known for babies, but Australian researchers say it can also deliver significant gains for athlets. They say an eight-week study of 40 atheletes showed those who had taken daily doses of cow colostrum-- the secretion in the first days after birth that boosts an infant's immune system--had more stamina than others on a protein placebo. And they believe atheletes using the substance cannot be accused of doping because it is a natural food product with no known side effects.