In lactating dairy cattle, bovine somatotropin (bST) is a naturally occurring species-specific protein hormone and major regulator of milk production. It is produced in the brain and coordinates metabolism to allow more nutrients for milk production.
Recombinant bovine somatotropin (rbST) is a synthetic version of bST which is primarily injected into dairy cattle to increase their milk production. Since the 1970’s it has been synthesized in the lab and, in 1993, approved by the FDA as safe for use and for commercial sale.
rbST works by increasing milk production in lactating cows and is administrated during week 9 – 10 of the natural lactation cycle (peak) and continued every two weeks until the end of lactation. rbST increases the efficiency of nutrient utilization by keeping milk producing cells alive and active longer, resulting in higher lactation persistency and therefore, a higher milk yield.
bST or rbST is metabolized in the liver, where Insulin-like Growth Factor-1 (IGF-1) is released and circulated to milk duct tissues. IGF-1 is a secondary hormone produced by mammals in response to levels of natural growth hormones (bST) and coordinates cellular growth and function. The addition of rbST stimulates more production of IGF-1, which circulates to milk duct tissues.
The molecular structure of bovine IGF-1 and human IGF is identical and the amounts of IGF-1 in cows treated with rbST are within the normal range of that found in untreated cows. According to the FDA, rbST is orally inactive in humans and therefore should not have any physiological effect on the human body from consumption of milk.
There is no scientifically proven, FDA-approved test for cows’ milk to determine whether the cows have received rbST supplementation. The lack of a test is not surprising because there are no differences in the composition of the milk — neither the macro-components nor the micro-components. Consumer confidence in food tests is maintained knowing that FDA requires rigorous proof before certifying the validity of such tests.