I've seen the following sort of blurb on a lot of milk products, saying:

"Our pledge: Milk comes from cows not treated with the rBST growth hormone"

If they indicate this, does that mean there's some sort of downside with treating a cow with recombinant bovine somatotropin (rBST) growth hormones? Are there any reported instances where non-rBST treated cow's milk are better than rBST treated cow's milk?

  • 3
    It actually says (at least in California) on the milk carton that there is no difference between milk from cows treated and not treated with rBST.
    – Publius
    Apr 8, 2013 at 4:40
  • It would be better if you could directly quote from one or two products, or even better if you could point to claims on their web-site. The quote, at the moment, doesn't claim any health difference. (e.g. consider the advertising of free-range eggs - generally, there are no claims that free-range eggs are healthier, just that they are more ethical.)
    – Oddthinking
    Apr 8, 2013 at 4:41
  • @Avi No it doesn't. The FDA-suggested disclaimer is “No significant difference has been shown between milk derived from rbST-treated and non-rbST-treated cows". FYI in 2008, in Ohio case International Dairy Foods Association v. Boggs, the 6th Circuit disagreed, citing increased levels of the hormone IGF-1, a period of milk with lower nutritional quality during each lactation, and increased somatic cell counts (goes sour more quickly).
    – smci
    Jul 9, 2018 at 0:48
  • The US FDA is not the only regulatory agency, and rBGH milk is essentially banned in Canada, Japan, the entire EU, Australia and New Zealand. Canadian scientists said the US FDA approval was a facade
    – smci
    Jul 9, 2018 at 1:00

2 Answers 2


From calsunshine.com:

The United States Department of Agriculture (USDA) determined that because rBST is a species-specific growth hormone, milk from rBST treated cows is identical to that of cows not injected with the hormone.

However, the US Court of Appeals for the 6th Circuit has held in Int’l Dairy Foods Ass’n et al. v. Boggs (pp. 9-10):

[A] compositional difference does exist between milk from untreated cows and conventional milk.


As detailed by the amici parties seeking to strike down the Rule, the use of rbST in milk production has been shown to elevate the levels of insulin-like growth factor 1 (IGF-1), a naturally-occurring hormone that in high levels is linked to several types of cancers, among other things


According to these studies, milk produced during this stage is considered to be low quality due to its increased fat content and its decreased level of proteins. The amici further note that milk from treated cows contains higher somatic cell counts, which makes the milk turn sour more quickly and is another indicator of poor milk quality. This evidence precludes us from agreeing with the district court’s conclusion that there is no compositional difference between the two types of milk.

  • 2
    Yes, but this has been challenged by the Appeals court. Courts aren't a great place to resolve science, but there is more to it that just one line about the USDA.
    – Oddthinking
    Apr 8, 2013 at 5:01

tl;dr There are differences, but none which ought to have or have been shown to have a meaningful impact on health.

Relatively current research indicates that fatty acid composition varies a small amount between cows treated with rBST and those that are not (and note that this study was on produced milk, so other practices that correlate with rBST usage may actually be causal). The differences are of a few percentage points at most, and are quite unlikely to be significant factors in health. A broader look at various compounds found very little difference in practice between the composition of milk (on average) from sources that used rBST and those that did not.

Also, most of the rBST itself that made it into the milk is destroyed during pasteurization.

So the answer is tentatively "yes there are detectable differences, but not any that ought to impact health".

Note however that rBST causes health complications in cows. So you might want to avoid rBST milk because you prefer not to obtain milk from cows that are even less comfortable than normal, but it is probably not rational to avoid it for health reasons unless you habitually alter behavior to avoid even low-risk events.

  • I believe the "health complications" bit is considered notable because some of those complications lead to increased use of things like anti-biotics. So while the rBST does not effect the milk, in isolation by itself, the claim would be that its use causes other substances to be used that might not be, otherwise. Jun 20, 2017 at 19:27

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .