Added hormones in poultry, pork, beef, and dairy

Glass of milk“This milk was produced without rbST*” (*No significant difference has been shown between milk derived from rbST treated and non-rbST treated cows). I see this on the milk jug every day, as most dairy products in California bear this label. It’s ironic to have a disclaimer for something that is absent: added hormones (in this case, rbST).

So why is there a disclaimer? Are added hormones in agriculture actually bad? Do hormones in milk cause kids to grow faster and earlier? Are we pumping chickens with hormones to get them so huge? These are questions that many parents struggle with today, as they navigate the complex labels on meat and milk.


There are no added hormones in your poultry, because the US Department of Agriculture (USDA) banned added hormones in poultry in the 1950’s. This regulation covers both organic and conventional poultry. The USDA mandates that when companies use the label “No hormones added” they MUST add a disclaimer stating “Federal regulations prohibit the use of hormones”. So, if you’ve been paying extra for chicken or turkey that’s labeled “No Added Hormones”, then that’s money wasted.

You might ask, “if we aren’t pumping chickens with hormones, then why are chickens and turkeys so much larger today”? It comes down to genetics and breeding. Before the 1950s, most farmers raised chickens for both eggs and meat, but eventually animal agriculture shifted in practice and farmers raising chicken for meat began choosing larger chickens to be “broilers.” Chicken farmers chose their broiler chickens for their genes to give us larger chickens that grow more quickly. These chickens aren’t “GMO,” at least not as “GMOs” are defined today.

Whether breeding large chickens is humane is an important question that should be considered. Society should focus on this legitimate issue rather than myths of hormones in poultry.

Increase in the size of broiler chickens from 1957-2005 due to breeding. Figure from Poult Sci. 2014;93(12):2970-2982. doi:10.3382/ps.2014-04291


Guess what? The use of hormones in pigs is also banned, and labelling carries the same requirements as poultry, listed above.

Beef and Dairy

Hormones in beef cattle

Hormones are provided to beef cattle so that they grow more efficiently. This allows the cattle to grow quicker using less feed. The University of Georgia’s Agricultural Extension program highlights that this is one of “the most economically justifiable practices available in the beef industry.” A recent study examined the environmental footprint of beef production with and without hormone implants. The authors estimated that the use of hormones reduce greenhouse gas emissions by ~5%, highlighting that it is an agricultural practice of environmental importance, too.

The hormones used in beef production are estrogen, testosterone, or progesterone, or their synthetic versions. These are provided to cows via an implant, that is placed under the skin behind the animal’s ear. The FDA highlights that the ears are discarded after slaughter, so it’s highly unlikely you’d ever consume that implant.

According to the FDA, the meat from these animals is safe for consumption at any time. In other words, you don’t have to wait until the implant is removed and hormone levels decrease before slaughtering the animal. In addition, the hormones that these animals naturally produce is much greater than the amount added, and these naturally occurring hormones do not harm the animals or the environment. As a result, hormone levels measured in cow muscles (which is what we eat) don’t change significant before and after hormone treatments (see page 10 of this document).

The table below highlights the amount of estrogen that is present in 500g of beef (1.1lbs) from a cow that has had an implant: as you can see, the amount is minimal relative to the amount of estrogen that is naturally produced in our bodies (table is modified from this paper).

Hormones in dairy cows

bST or Bovine Somatotropin is a cow growth hormone that increases milk production. Its engineered version is known as rbST or recombinant bST. Studies have shown that using rbST in dairy production can improve dairy’s carbon footprint by decreasing the amount of feed given to animals, water use, cropland, and greenhouse gas emissions.

The FDA has determined that bST is safe for human consumption because the bST hormone gets broken down when we ingest it. Additionally, the hormone is quite different from human somatotropin, so our bodies do not recognize it. These findings were supported by the World Health Organization’s Food and Agriculture Organization (FAO) of the United Nations. This agency reiterates that the human and bovine receptors and hormones are different from one another.

Imagine that somatotropin from cows is circular, whereas human somatotropin is triangular. Each organism’s hormone receptor binds a hormone of a specific shape: the human receptor could only bind a triangular hormone, and the bovine receptor only binds a circular hormone. So a circular hormone in our bodies wouldn’t be recognized by the triangle-binding receptor and ends up getting digested like any other protein.

The FAO highlights that the amount of bST found in the tissues and milk in cows that are treated with rbST compared to cows that don’t receive the hormone is quite similar. They also point out that cooking and pasteurizing breaks down the hormone, as does regular digestion in our guts.

Other data that FAO reviewed include:

  • a 2 year carcinogenicity study in rats and mice, using the appropriate hormone equivalents which found no evidence that injections of somatotropins cause cancer.
  • Data suggesting that “there is no significant change in the concentrations of total bST detected in milk and tissues of rbST treated cows when compared with untreated controls”.

Why is there concern over rbST?

rbST has been banned in various countries, including Canada and the EU (note that with recent changes in trade deals, these may be changing). The Veterinary Drugs Directorate of Health Canada reviewed rbST in 1990 and stated that there were no concerns for human safety, but rather, for animal welfare. Add to this the fact that rbST was owned by Monsanto for a time, a corporation whose name has a very negative connotation with the public, and you get a recipe for fear. So what’s true? Why is rbST banned in many countries?

rbST increases milk production and studies have shown that this can lead to a type of inflammation of the mammary gland and udder tissue, known as mastitis. Mastitis is often caused by bacteria. Some studies have shown that the increased milk production has other consequences, such as foot disorders and reproductive problems. However, while many early studies found that rbST increased the risk for mastitis, including Monsanto’s own data, more recent studies and reviews have found no difference in the the risk for mastitis between cows that receive rbST and cows that do not.

I reached out to Carrie Mess, otherwise known as Dairy Carrie, to ask her about the use of rbST on the farm. She also said that while increased milk production can impact mastitis, that could be said about a lot of different things, including farming practices that improve the dairy cows’ comfort. Basically, happier cows produce more milk. Consequently, anything that makes the cow happier and more comfortable will increase the amount of milk produced and could indirectly cause mastitis. However, she stressed that we do not point to these and say, for example, that “better forages cause mastitis”. Consequently, milk production and its increase are part of proper farm management. Carrie noted that her farm discontinued the use of rbST, and they didn’t see a change in the incidence of mastitis.

I also contacted Dr Alison Van Eenennaam at UC Davis. She reiterated that while there’s a tendency for mastitis to increase with milk production, it cannot be said that rbST causes mastitis. Canada’s parliamentary research documents on rbST support this statement by clarifying “since rbST-treated cows produce more milk, it has been suggested that the increased incidence of mastitis could be due to this higher level of production, rather than to the hormone treatment.”

Dr Van Eenennaam also mentioned that improved genetics over the years have allowed for the selection of cows that do not get mastitis as easily. She stressed that rbST allows for increased efficiency, which translates to fewer cows required and decreased greenhouse gas emissions.

However, the European Union’s summary points out that the incidence of mastitis may be quite under reported, and recommended its ban. Since the ban in EU was for purposes of animal welfare, the import of dairy products produced with rbST is permissible. The same is true in Canada.

In writing this piece, I found myself torn. I understand that mastitis can be caused by many factors that lead to increased milk production and that farms must ensure it doesn’t happen. But on the other hand, rbST can be one such factor. Given the climate crisis, making dairy more efficient is increasingly urgent and the use of rbST would be an effective means of increasing efficiency. Perhaps the knowledge we’ve gained in the last two decades would allow us to reexamine the question of rbST and implement the hormone in a responsible manner.

Do animal hormones cause early puberty?

The leading concern I’ve heard from parents is that animal hormones will impact their children, and particularly that they’ll cause early puberty. Is this true? Do children today hit puberty at an earlier age?

Yes, children are exhibiting signs of puberty at an earlier age. There are several studies that have found that pubertal development has changed, but looking at the data, you can clearly see that this trend began decades before the use of hormones was introduced into agriculture, and is seen in countries where rbST was never introduced. So hormones in meat or milk aren’t to blame.

The one consistent factor that has been highlighted as a potential cause of earlier pubertal development in both girls and boys is nutrition and obesity. Nutrition during childhood can account for “25% of the variation in the timing of puberty”. Puberty is further accelerated with obesity. We see this not only in Europe and North America, but in other countries as well: this recent study from South Africa found that both height and BMI predict early pubertal development. In Nigeria, socio-economic class was associated with early puberty, which again suggests that nutrition is an important factor.

These data are further evidence stressing the importance of proper nutrition in our children, avoiding excess sugar, and getting sufficient exercise.

Key Points

  • Poultry and pork do not have any added hormones.
  • Beef can have added hormones, but no impact has been seen in humans or on animal welfare.
  • Dairy in the United States can have added hormones, but they are seldom used.
    • Hormones used in dairy have not been shown to impact human health, including developing children.The addition of hormones to dairy cows is one of multiple factors that can lead to increased milk production, and needs to be managed carefully by dairy farmers to ensure that there’s no negative impact on the animals, particularly mastitis.
  • It must be stressed that reducing the consumption of red meat and processed meats is recommended, as these have been associated with specific cancers. The absence of added hormones in meat does not reduce this risk.