What is rbST?

Bovine somatotropin (bST) is a hormone produced in a cow’s pituitary gland, which is located at the base of the brain. Somatotropin is naturally produced in all cows. Somatotropin regulates the cow’s metabolism and determines how efficiently the cow converts feed into milk. Bovine somatotropin (bST) is also called Bovine Growth Hormone (bGH).

Dairy farmers can now inject cows with a man-made version of bovine bST called recombinant bST (rbST). To develop bovine rbST, scientists used special DNA techniques for bacteria to produce large amounts of bovine rbST. Bovine rbST has the same structure as natural bovine bST.

How does rbST work?

Administration of rbST helps dairy cows produce more milk for more people. When cows are administered rbST, they convert feed into milk more efficiently. Cows only produce milk after having a calf, and their milk production usually declines by 60 to 90 days after having the calf. If the dairy farmer begins administrating rbST to a cow around day 57 of lactation, the cow can make more milk for a longer period of time. With rbST, the average cow can make an extra gallon of milk each day.

This increase in milk production and efficiency means that milk production can be more environmentally sustainable. By using rbST, dairy farmers need fewer cows, less land, less water and even less feed.

Is rbST safe for humans?

Human growth hormone is very different in structure from bovine growth hormone and bovine rbST. The differences in the DNA structure of natural human bST and natural bovine bST means this bovine growth hormone (rbST) cannot work in the human body.

Some worry that humans could be affected by an increase in the bovine insulin-like growth factor-1 (IGF-1) when using rbST for milk production. Though some early studies found a link between IGF-1 and certain tumors, later studies found weaker links and failed to confirm those findings. According to the U.S. Food and Drug Administration (FDA), studies show that IGF-1 levels in cows using rbST are within the range of levels of IGF-1 found in cows not using rbST.

These concerns over human health were thoroughly investigated by the U.S. Food and Drug Administration during the approval process for rbST. Over the course of nine years, the FDA studied whether rbST had any effect on different parts of the human body, infants or children. After reviewing the data, the FDA approved the use of rbST in 1994 for lactating dairy cows.

Is rbST safe for cows?

Some scientific studies have found a connection between rbST use and an increased incidence of mastitis in dairy cows. In cows, mastitis is an infection of the udder or mammary gland tissue. Recent studies evaluating rbST and mastitis have shown mixed results.

Because mastitis is an infection, some consumers worry that milk from cows having mastitis could contain antibiotics or antibiotic-resistant bacteria. It is important to remember that all milk in the United States is tested for antibiotic residues. All contaminated milk is discarded before it reaches the food supply. Research on antibiotic-resistant bacteria is ongoing, but academic scientists and the FDA have found no link to date between rbST use and antibiotic resistant bacteria.

Why choose not to use rbST?

Whether or not to administer rbST to lactating dairy cows often comes down to economics.

Certain retailers and dairy companies require farmers to not use rbST on their dairy cows. For example, Costco’s “Kirkland” brand does not use milk from rbST cows. Companies are often willing to pay a higher price for non-rbST milk. But not using rbST means dairy farmers will also produce less milk for human consumption and have lower incomes.

These decisions can also affect consumers. Milk from non-rbST cows usually costs more at the grocery store.

In the United States, consumers can buy milk from rbST-cows and non-rbST-cows. Some companies label their milk as “rbST free” or “rbGH free.” However, because scientists have found no differences in milk from rbST cows compared to no rbST cows, many labels also say, “No significant difference has been shown between milk derived from rbST [or rbGH] cows and non-rbST cows.”

Learn more about why farmers choose to use rbST

Learn more about how rBST affects the dairy industry