Colostrum is a pre-milk fluid produced in the mammary glands of mammals that have recently given birth. Newborns have immature digestive and immune systems, so the enzymes, antibodies, and growth factors colostrum provides promote growth and fight disease. Though colostrum is produced by all mammals, colostrum supplements are usually derived from bovine or (less frequently) goat sources. Colostrum has become a popular nutritional supplement because it is a rich source of enzymes, antibodies, and growth factors not found in other dairy products.
The undeveloped intestinal tract of a newborn allows the growth factors present in colostrum to pass freely through the intestinal wall for absorption. However, fully-developed adult mammal intestines will break down the beneficial compounds before they can be absorbed into the blood stream. Though digestive enzymes prevent colostrum growth factors from affecting muscles, they will still exert a local effect, which increase intestinal integrity. This prevents inflammation, like the kind that can be caused by prolonged, intense exercise, like competitive cycling. Outside of intense exercise, supplementing colostrum will have an effect similar to supplementing whey protein or casein protein.
Athletes often supplement colostrum in an effort to increase fat burning, add lean mass, or increase strength. Since their digestive systems are fully developed, these effects do not occur, and the body breaks down the growth factors and enzymes that colostrum provides before they can be transported to muscle cells.
The antibodies present in colostrum are also effective at reducing diarrhea caused by Escherichia coli and reducing the risk of HIV infection. To prevent E. coli-induced diarrhea, the colostrum must be obtained from an immunized animal.