Hormone Use In Dairy Cows

Since farmers started using hormones to increase their cows’ milk production, there has been a lot of debate over whether these hormones in milk are safe or not.

This milk is pretty clearly labeled that it from cows not treated with rbST.

chocolate milk no rBST

But what that asterisk indicates is on the back of the package, in font that does not stand out quite so much. “No significant difference has been shown between milk derived from rbST treated and non-rbST treated cows.”

no difference in BST

One of the first things I found when researching for this post was another post about this very thing by a woman who is a mom and a scientist on Science of Mom. This is a very well-written post, and I strongly recommend that you go read that. (Then come back.)

These are the most common questions that I hear about the use of hormones for dairy cows.

What hormones are farmers using in dairy cows?

Some farmers give a hormone called recombinant bovine somatotropin (rbST). Cows already make bovine somatotropin (bST). The rbST is made with the same techniques that are used to make insulin to treat diabetics. rbST is the same hormone as the naturally-occurring form that is already in the cows.

Do the hormones that the cows are given get in my milk?

The very short answer is no. All milk has some hormones in it, and all milk has bST. There is no test that can tell the difference between a cow’s natural bST and rbST. Milk from cows not treated with rbST has around 1 nanogram of bST per milliliter of milk. (That’s one part of hormone per one billion parts of milk.) Milk from cows treated with six times the normal dose of rbST (in studies looking at the safety of this hormone for cows and people) can have up to 3 nanograms of bST per milliliter of milk, but we’re still only talking 3 parts of hormone per one billion parts of milk. Whether or not a cow was treated with rbST, the total amount of bST in her milk is less than 0.000001% of all the protein in her milk.

Is the milk from cows that were given these hormones safe, or any different from milk from cows that were not given these hormones?

Regardless of whether or not the hormone gets into milk, the bottom line is that bST and rbST are not active in people. People make their own version of somatotropin (also called growth hormone). Growth hormones, or somatotropins, are species-specific, which means that they do not have activity in other kinds of animals.

Also, bST is a protein hormone. And like any other protein, it gets broken down into the many different amino acids that fit together like a puzzle to make the hormone in our stomachs. The protein hormone is only active when the puzzle is complete – bits and pieces of the puzzle have no activity by themselves.

Are these hormones safe for the cows?

Early studies looking at the safety of rbST in cows showed that there might be an increased incidence of mastitis (infection of the udder) in cows that were given rbST. Later studies, and time using rbST has shown that cows do not have a higher risk of mastitis, and there are no significant health risks for cows that receive this hormone.

How does bST work?

bST (and rbST) act on the mammary gland (udder) to help it take up more nutrients from the cow’s bloodstream. This helps the udder to make more milk. A cow that is given rbST can make around 10 more pounds of milk per day (that’s around 1 gallon) than a cow that is not given rbST.

Of course, if she’s making more milk, she needs to eat more to make up for those calories. A cow will need to eat 1 more pound of food for every 2 pounds of milk she makes, so the cow who makes 10 more pounds of milk a day will need to eat 5 more pounds of food a day.

If a cow is not in good health, or does not have a good diet, the rbST is not going to help her make more milk. It’s not a “magic bullet” that automatically makes every cow into a “milk making machine.” It is one tool that farmers have to help their cows “be all they can be” – and a farmer needs to use all his tools together for the best results.

Why are farmers giving these hormones anyway?

rbST is one way farmers can help reduce the environmental impact of farming. Dairy farmers are already amazing environmental stewards – they do everything they can to reduce the amount of resources they use, and they recycle everything they can. (Remember how New Generation Dairy recycles the water they use to cool their milk, and the types of feed they use from other areas of agriculture?)

With selective breeding to maximize a cow’s genetics, dairy farmers are already able to use less land and water to make milk. Using rbST gives farmers another environmental advantage, so they can conserve resources even more.

What’s my choice?

I don’t have a problem drinking milk from cows that were treated with rbST, or giving that milk to my family. But my choices are limited! Many milk processors and grocery stores have chosen to only use milk from farmers who choose not to use rbST. I don’t go out of my way to buy milk from cows that were treated with rbST, I buy what is convenient for me at my local grocery stores. But if my convenient option was milk from cows treated with rbST, that would be okay with me!

no rBST in milk

What’s your choice? Do you have a question I didn’t answer? Let me know!


Large animal veterinarian, cattle farmer, pet owner, grocery buyer.

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