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Part 5 | rbST: Friend or Foe?

In the fifth article of this series about recombinant bovine somatotropin (rbST), we will further discuss frequently asked questions from farmers. These questions are also important when talking to milk buyers, especially regarding milk composition, milk quality, and somatic cell count (SCC).


The answer is a definite no! When a cow is sick, stressed, or uncomfortable, her production will drop, and feed efficiency will decline. Bovine somatotropin (bST) is a natural protein present in the bloodstream of lactating mammals, with the highest concentration after calving. By injecting rbST, the high concentration of bST is extended, thus increasing the milk yield. Injecting rbST into well-managed cows will increase their production to the same level of cows already producing high yields. The health of rbST-injected cows will be the same as those high-producing cows and should, therefore, be treated the same way. In general, cows only increase their production when they are happy and healthy.


Without rbST, milk composition and quality varies naturally, depending on age, lactation

stage, feed type, genetics, breed, and a number of other factors. Injecting rbST does not affect milk composition in terms of fat, protein, lactose, or even vitamins and minerals. Milk composition is only affected by the factors that normally influence it, with or without rbST. Soliman and El-Barody (2013) showed that if milk yield increased, milk composition does not change. It only increases in proportion to the yield. Recombinant bovine somatotropin does not influence milk composition, processing properties, or taste.


Mastitis is one of the most expensive and frequently treated diseases on the farm. It is quite normal to wonder what the effect of higher milk yield will be because of using rbST. Several studies have shown that mastitis is not caused by rbST. Normand et al. (2014) showed that the incidence rate of clinical mastitis did not differ significantly between rbST-treated or rbST-untreated cows, however, injected cows did produce more milk.

yield, the more chance there is to have mastitis in the herd. Baumen (1992) showed that the effects of rbST are small and equate to an annual increase of 0,4 cases per cow for each 1 000 kg of genetic gain in milk yield.


To conclude, rbST may be seen as a complex and very controversial product, but the facts clearly prove that it makes farms more profitable, efficient, and sustainable. Farmers need to look at technology and, in this case, biotechnology, e.g. rbST.



  • Bauman, D.E. 1992. Bovine Somatotropin: Review of an emerging animal technology. Journal of Dairy Science 75: 3432 – 3451.

  • Bauman, D. 2015. Facts about recombinant bovine somatotropin (rbST). Date of Access: 16 Mar. 2022

  • Bovine somatotropin. NIH Technol Assess Statement Online 1990 Dec 5-7 [2022, 6 June]; (7):16

  • Chilliard, Y. 1988. Long-term effects of recombinant bovine somatotropin (rBST) on dairy cow performance. Annales de zootechnie, INRA/EDP Sciences 37(3): 159 – 180.

  • Huber, J.T., Fontes, W.C., Sullivan, J.L., Hoffman, R.G., and Hartnell, G.F. 1997. Administration of recombinant Bovine Somatotropin to Dairy Cows for Four Consecutive Lactations. Journal of Dairy Science 80(10): 2355 – 2360.

  • Normand R.St-Pierre., Milliken, G.A., Bauman, D.E., Collier, R.J., Hogan, J.S., Smith, K.L., and Thatcher, W.W., 2014. Meta-analysis of the effects of Sometribove zinc suspension on the production and health of lactating dairy cows. JAVMA 245(5): 550 – 564.

  • Raymond, R., Bales, C.W., Baumen, D.E., Clemmons, D., Kleinman, R., Lanna, D., Nickerson, S., and Sejrsen, K. 2021. 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. Montreal, Canada, 14 July 2009.

  • Santos, J.E.P., Juchem, S.O., Cerri, R.L.A., Galvão, Chebel, R.C., Thatcher, W.W., Dei, C.S., and Bilby, C.R., 2003. Effect of bST and Reproductive Management on Reproductive Performance of Holstein Dairy Cows. Journal of Dairy Science 87(4): 868 -880.

  • Soliman, E.B. and El-Barody, M.A.A., 2013. Physiological responses of dairy animals to recombinant bovine somatotropin: A Review. Journal of Cell and Animal Biology 8(1): 1 – 14.

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