Colostrum
(Bovine, sheep)

The production of colostrum in a pregnant cow begins about 3 to 4 weeks before birth when growth factors from the cow's body stimulate the development of specific receptors on the surface of the cells lining the mammary glands. These activated receptors facilitate the transfer of immune antibodies, hormones and other important growth factors from the mother's blood into the colostrum that is developing in the breast. This process is how a mother transfers her immunoglobulins, such as IgG, IgA and IgM antibodies to her infant, which conveys passive immunity and initiates the development of a healthy immune system. This process is much the same in humans.

About two days before birth, hormonal changes cause a sharp decline in colostrum production and signal mammary cells to begin producing a different mix of substances, including lactose. At birth, progesterone levels fall dramatically and one of the consequences of this change is that cells lining the mammary glands receive a signal that essentially blocks any further transfer of substances from the mother's blood into the breast. Hence, the fluid that is in the breast at the time of birth is true colostrum. Milking during the first six hours removes approximately 80% of the true colostrum. Subsequent milkings contain much less colostrum as milk production dilutes the colostrum that was left in the mammary glands.

It is important to realize that nature has designed colostrum to be the first food ingested by newborn mammals. In addition to nutritional factors, colostrum is reported to contain many other important constituents such as antibodies, enzymes, proteins, and growth factors. These factors play an important role in various aspects of an infant's growth and development.

An important issue differentiating the various commercial colostrum products is the time of collection. Colostrum is generally recognized as the fluid that is delivered from the breasts during the first 24 to 48 hours. However, research documents the fact that the concentration of active substances is much greater within the first six hours. Thereafter, the amount of active substances unique to colostrum declines rapidly as lactation begins the process of producing milk in the breasts. For example, at 6 hours, the total protein content, which contains the important immune components, is 49% of the total dried colostrum. At 24 hours, the total protein content has dropped down to 35% of the total dried colostrum.(4) In another example, the first milking after calving yielded 248-1850 ng/ml of Insulin-like Growth Factor-1 (IGF-1) and 12.4-42.6 ng/ml of Transforming Growth Factlor-beta (TGF-beta). However, the fifth milking only contained 27-101 ng/ml of IGF-1 and 0.80-3.49 ng/ml of TGF-beta.(5)

Colostrum also contains elevated concentrations of important hormones and growth-promoting peptides, such as insulin, cortisol, epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I), which play important roles in the developing newborn.(6) Studies have not been conducted to determine t