Today’s guest post comes from a dear friend of mine, Dr. Katie Schoenberg. Katie and I overlapped during our undergrad years at Cornell, but I didn’t actually meet her until we worked together in the Nutrition Lab at Smithsonian’s National Zoo, the first job out of undergrad for both of us. We bonded over analyzing desert tortoise urine and freeze-dried sea urchins (yes, really), and we had enough fun that we both stayed in science! Katie went on to earn her M.S. at University of Maryland and her Ph.D. from Cornell University, where she is currently a postdoc. She’s also a new mom to a beautiful 11-week-old daughter.

I invited Katie to write a guest post for ScienceofMom a while back, and lucky for us, she agreed. Katie’s research is focused on dairy cows, so I asked her what she thought about the safety of milk from cows treated with rbST. Being a stellar scientist and a conscientious mom, I knew I could trust her to give us the low-down on rbST. I’m especially grateful to Katie for putting this post together during her maternity leave, between diaper changes and feeding her baby girl. Her answer to this question may surprise you, and I look forward to hearing your thoughts about how you make food-buying decisions for your family.

Truth from the Dairy Aisle: Is Milk from Cows Receiving rbST Safe for my Family?

By Katie M. Schoenberg, Ph.D.

I have a B.S., M.S., and PhD in Animal Science and study the nutrition and metabolism of dairy cattle. Recently, I gained a new title: Mom. Throughout my pregnancy and during the first 11 weeks of our daughter’s life I have enjoyed combining my zeal for the scientific method, my scientific expertise in pregnancy and lactation, and my newly acquired non-fact-based (though hormonally driven) motherly instinct. This has persuaded me to revisit my own truth on an issue that I have thoroughly researched in the past: the safety of the use of recombinant bovine somatotropin (rbST, also referred to as growth hormone or bGH) in the dairy cows producing the dairy products we consume. As a new mom, now responsible not only for making healthy choices for myself but also my child, would I feel the same way about the safety of rbST?

Let’s begin with a brief introduction to the lactation cycle of dairy cattle. Just like human moms, bovine (that’s a fancy word for cows) moms start producing milk when they give birth. For about the next 10 months, a cow will produce milk that ends up in your grocery store dairy case. Then, she’ll take a couple of months off to prepare for the birth of her next calf, when the cycle begins again.

All cows already have bovine somatotropin in their bodies. After decades of scientific research, scientists recognized that cows supplemented with additional somatotropin produce on average 10-15% more milk every day1,2. This reduces the number of cows and the amount of land, water, and resources needed to produce the same amount of milk3. From a farmer’s (and consumer’s) perspective this is a positive in terms of business and environmental impact.

Cows that are given rbST (approved and used commercially since 1994) receive an injection of 500 mg (slow release) once every 2 weeks beginning around 9 weeks into lactation. This recombinant somatotropin (ST) is a hormone produced by the same process used to make insulin for Type I diabetics: recombinant bacteria. In essence, the gene to produce bovine ST is engineered into bacteria that generate the hormone, which is then harvested, purified, and packaged. The fact that the bacteria are producing the bovine form of the hormone has an important implication: The bovine form of ST is NOT recognized by receptors in the human body. This means that even if you injected yourself directly with a shot of rbST, it can’t have a biological impact on human cells.

That’s what rbST is and what it does for the cow, but how does it affect the milk that you and your children ultimately consume? In 1985 the FDA determined that milk, meat, and other products from animals that have been given rbST was safe for human consumption. The FDA continues to revisit the safety and efficacy of rbST regularly4,5. The FDA and other agencies such as the National Institutes of Health6 stand by rbST as being a safe and effective tool for dairy farmers to use to enhance the productivity of their dairy cattle.

The use of rbST is safe, because it does not change the composition of milk in a biologically relevant manner. In fact, there is no laboratory test that can tell whether milk came from a cow treated with rbST or not. This is the reason that the “hormone free” labels say “our farmers pledge” rather than “guaranteed.” There are several summary reports on the compositional differences in milk, such as the one published in the Journal of the American Medical Association in 19907. All cow milk contains bovine ST, no matter how the cows are managed. Cows administered rbST at levels 6 times the dosage given to cows today causes a slight increase in ST in milk7. However, recall that rbST is species-specific and is not recognized by the human body.

There’s another reason why I’m not concerned about a little bit of rbST in milk: The rbST hormone is a protein. When ingested by mouth, it is digested and broken into constituent amino acids in your GI tract, just like every other protein eaten, and therefore results in zero impact as a growth hormone. Even if it did survive digestion, your body wouldn’t recognize bovine ST, because its structure is only recognized by receptors in the cow.

This leaves two main arguments against the use of rbST8: 1) Increases in the milk concentration of insulin-like growth factor-I (IGF-I), another hormone regulated by ST; and 2) Increases in incidences of diseases such as mastitis (infection of the mammary gland) in dairy cattle.

Milk from cows administered rbST has been shown to have up to 2-fold higher levels of IGF-I9. Unlike rbST, IGF-I, is not species-specific, so at first glance, this may be concerning. However, IGF-I makes up only 0.00003% of milk proteins, and like all other proteins it is also broken down by digestion. In addition, you would have to drink 1L of milk to equal the amount of your own IGF-I present in the saliva that you swallow on a daily basis6. Furthermore, cows administered rbST have milk IGF-I concentrations within the normal range based on individual and day of lactation variation (1.27 – 8.10 ng/mL)10. There are also several other studies which have shown that rbST administration doesn’t affect IGF-I concentrations in milk and that concentrations mirror the normal pattern of IGF-I secretion in cows not receiving rbST10. For these reasons, I’m not concerned about IGF-I in my milk.

Lastly, I will touch on the effects on the health and wellbeing of the cows only briefly as ultimately this may be a social issue (vs. a health issue related to our children). Use of rbST on farms does not lead to increased incidences of health problems in dairy cattle. One study found no difference in the incidence of mastitis infections between cows that were or were not treated with rBST11. In another study, observation of over 1000 cows showed no significant effects of rbST administration on cow health, nor how long cows were in a herd12. The biology of how rbST works demands that cow health and nutrition must be of the highest standard in order for rbST to increase milk production. With poor cow health and nutrition, the farmer is throwing away money administering rbST. I would argue then, that herds that use rbST improve the health and wellbeing of their animals to take advantage of the efficiency improvements from rbST.