Protecting health and safety is important for animals, too.

Get the inside scoop on dairy farming and cows treated with rbST.

What’s the deal with rbST treated cows?

Like all mammals, cows naturally produce a hormone that tells their bodies to produce milk. In cows, it is called bovine somatotropin (bST).2,3 Recombinant bovine somatotropin (rbST) is a hormone that is a biologically equivalent to bST, meaning the cow’s body treats and processes this hormone the same way it processes naturally-produced bST and other protein hormones.4

Why are cows treated with rbST?

In addition to good feeding and care, farmers use products like rbST to help cows maintain milk production without changing the safety and quality of dairy products we consume. When farmers supplement cows with rbST, the cows are able to safely produce about one gallon more milk per day.

Healthy food is just as important as a healthy farm. Over 200,000 more cows would be needed to meet our standard level of dairy production without rbST.

Is rbST safe for cows?


rbST does not present any greater risk of painful conditions for cows. When used properly, reactions to doses are rare.


In a recent comprehensive meta-analysis, rbST supplemented cows had no greater risk of mastitis, lameness, or removal from the herd.

St. Pierre et. al., 2014 JAVMA


While the use of rbST may alter a cow's reproductive rate, these potential effects are both well understood and easily manageable.

cow world

Who regulates rbST?

The U.S. Food and Drug Administration (FDA) has a stringent approval process for veterinary medicines – much like that for human medications. Products used in animals require the same testing as those used in humans, with the additional requirement that they must be tested to ensure resulting food products from the animal will be safe for human consumption. Posilac® was approved by the FDA in 1993.

Posilac® is injected every 14 days starting 57–70 days after calving until the end of lactation. The label contains complete use information including cautions and warnings.

Want more details?

To find out more about rbST and animal health, check out the News and Resources page.

  1. (formerly Dairy Facts. Farm Animal Education Network. Purdue University).
  2. Recombinant Bovine Somatotropin (rbST): A Safety Assessment. Joint Annual Meeting of the American Dairy Science Association, Canadian Society of Animal Science and American Society of Animal Science. Republished March 26, 2012.
  3. Etherton, TD and DE Bauman. Biology of somatotropin in growth and lactation of domestic animals. Physiol Rev. 1998 Jul; 78(3):745-61
  4. McGuire MA et al. Nutritional modulation of the somatotropin/insulin-like growth factor system: response to feed deprivation in lactating cows. J. Nutr. 1995 Mar; 125(3):493-502.
  5. Daughaday WH and Barbano DM. Bovine Somatotropin supplementation of dairy cows. Is the milk safe? JAMA. 1990 Aug 22-29; 264(8):1003-5
  6. Evaluation of certain veterinary drug residues in food. The seventy-eighth report of Joint FAO/WHO Expert Committee on Food Additives. World Health Organizations 2014.
  7. Vicini et al. Survey of Retail Milk Composition as Affected by Label Claims Regarding Farm Management Practice. J Am Diet Assoc. 2008 Jul: 108(7): 1198-203.
  8. bST Fact Sheet. Cornell University. 1995.
  9. Capper, JL et al. The environmental impact of recombinant bovine somatotropin (rbST) use in dairy production. Proceeding of the National Academy of Science. 2008 July; 105(28): 9668-73.
  10. St. Pierre et al, 2014 (meta analysis)
  11. Celebrating 20 years of Dairymen Making Positive Impacts with Posiliac. Elanaco. 2014.
  12. Dietary Guidelines for Americans 2010. U.S. Department of Agriculture. U.S. Department of Health and Human Services
  13. ACT-on-TechTM: Questions and Answers on rbST. Elanco. GMA Final. 10 June 2013.
  14. Kretchmer N. Why not have more milk? Pediatrics. 1991:88:1056-7.
  15. Hammond BG et al. Food safety and pharmacokinetic studies which support a zero (0) meat and milk withdrawal time for use of sometribove in dairy cows. Ann. Rech. Vet. 1990;21 Suppl 1:107S-120S.
  16. Steingraber S. The falling age of puberty in U.S. girls: what we know, what we need to know. Breast Cancer Fund. August 2007.
  17. NIH Technology Assessment Conference Statement. Dec. 5-7, 1990.
  18. Bovine Somatotropin (bST) The Basis ACT-on-TechTM. Elanco. GMA Final. 10 June 2013
  19. McGuire MA et al. Nutritional modulation of the somatotropin/insulin-like growth factor system: response to feed deprivation in lactating cows. J. Nutr. 1995 Mar; 125(3):493-502.
  20. 9 Food and Drug Administration, Center for Veterinary Medicine Advisory Committee. The effect of sometribove on mastitis. FDA report from the public hearing. 31 March 1993.
  21. 11 National Mastitis Council, Cow factors in mastitis; and management and environmental factors in mastitis. Current concepts of bovine mastitis. Chapters 5-6. Madison, WI. 1996.
  22. 12 Bauman, 1999

The label contains complete use information, including cautions and warnings. Always read, understand, and follow the label and use directions. Supplement lactating dairy cows every 14 days beginning at 57–70 days in milk until the end of lactation.