Colostrum is a thick yellow fluid, rich in protein, growth factors, and immune factors. It is secreted by the mammary glands of all female mammals during the first few days of lactation. It also contains essential nutrients and protease inhibitors that keep it from being destroyed by the processes of digestion. Humans produce relatively small amounts of colostrum in the first two days after giving birth, but cows produce about 9 gallons (36 L) of colostrum. Bovine colostrum can be transferred to all other mammals, and is four times richer in immune factors than human colostrum.

Although colostrum has received widespread attention as a dietary supplement only since the late 1990s, it has a lengthy history of medicinal use. Ayurvedic physicians in India have used colostrum as a treatment for thousands of years. In the United States, mainstream medical practitioners recommended colostrum as a natural antibiotic before the discovery of penilcillin and sulfa drugs. In the 1950s, colostrum was used to treat rheumatoid arthritis (RA). Dr. Albert Sabin, the researcher who developed the first oral vaccine for poliomyelitis, found that colostrum contains antibodies against polio. He recommended colostrum as a dietary supplement for children who were vulnerable to polio.

The major components of colostrum include the following substances:

• Immunoglobulins. Immunoglobulins are globulin proteins that function as antibodies. They are the most plentiful immune factors found in colostrum. Immunoglobulin G (IgG) counteracts bacteria and toxins in the blood and lymphatic system
• Lactoferrin. Lactoferrin is a protein that transports iron to red blood cells and helps to deprive viruses and harmful bacteria of iron.
• Proline-rich polypeptide (PRP). PRP is a hormone that regulates the thymus gland, helping to calm a hyperactive immune system or stimulate an underactive immune system.
• Growth factors. The growth factors in bovine colostrum include insulin-like growth factors (IgF-1 and IgF-2), an epithelial growth factor (EgF), transforming growth factors (TgF-A and TgF-B), and a platelet-derived growth factor (PDGF).
• Growth hormone. Growth hormone slows some of the signs of aging.
• Leukocytes. Leukocytes are white cells that stimulate production ofinterferon, a protein that inhibits viruses from reproducing.
• Enzymes. Colostrum contains three enzymes that oxidize bacteria.
• Cytokines and lymphokines. These are substances that regulate the body'simmune response, stimulate the production of immunoglobulins, and affect cell growth and repair.
• Vitamins. Colostrum contains small amounts of vitamins A, B12, and E.
• Glycoproteins. Glycoproteins, or protease inhibitors, are complex proteins that protect immune factors and growth factors from being broken down by the acids in the digestive tract.
• Sulfur. Sulfur is a mineral that is an important building block of proteins.

Colostrum is presently used to treat a variety of diseases and disorders. Applications that have been investigated in clinical trials include the following:

- Bacterial and viral infections
- Allergies and autoimmune diseases
- Heart disease
- Cancer
- Weight loss
- Sports medicine
- Open wounds