Colostrum is produced prior to birth of the calf for immediate protection of the newborn; the sooner it is harvested, the more valuable it is. Many companies claim “First” or “Six” but are unwilling or able to prove it. Others state that it is not even possible to collect the single first milking within 6 hours.
In the first milking collected within six hours, over 80% of the serum fraction is bioactive components produced in the bone marrow and circulatory system.
At the second milking collected between 12 and 24 hours, only 50% is considered bioactive.
Production of the whey proteins beta-lactoglobulin and alpha lactalbumin produced from amino acids in the alveoli of the mammary gland now account for the majority of the protein. While they have biological function in addition to their primarily nutritional role, these proteins are available in many consumer foods, whey protein concentrates and isolates.
When the transition to milk has been completed, the bio-actives are less than 1% of that contained in colostrum.
Because the transfer of all factors is not diminished at the same rate during the period after birth, 1st milking bovine colostrum has a different balance (ratio) of factors compared to the subsequent transitional period milkings as well.