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Part 3 | rbST: Friend or Foe

Updated: Aug 10, 2022

As part of a series of articles about recombinant bovine somatotropin (rbST), we explained in the previous issues the origin of rbST, why it is used, and what effect it has on the sustainability of dairy farming. In this article, we delve deeper, starting with the nutrition of rbST.


Milk production increases when cows are injected with rbST. When a cow’s milk production increases, so does her feed intake. The same happens when milk production increases due to rbST. Most research has shown that, as milk production increases, so

does feed intake gradually increase due to higher metabolic demand.

The same feed can be given to cows that are being injected with rbST, as there are no

special requirements. However, it is important to remember that the cow will need access to more feed to maintain the increased milk production. This increase in feed is to ensure that the demand for extra nutrients for milk synthesis is met and that the animal can maintain a higher milk production level without milking from her back.

Although there is a slight delay in the higher feed intake, extra nutrients can be provided

by body stores. During this period, the body undergoes coordinated changes in metabolism and the increased feed intake adapts to higher milk production. Thus, higher feed intake equals higher milk yield over the entire lactation.

When a cow consumes more nutrients than needed, she tends to gain more body condition because the extra nutrients are stored as fat. When rbST is injected, the extra nutrients are directed to milk synthesis rather than for body reserves, thus body condition is maintained.

Rule of thumb: for every liter increase in milk production, a cow will need an average of 200 - 300g extra feed.


Now that we know that cows increase their feed intake when injected with rbST, it is important to note that different farming techniques have an effect on the response of rbST. The increase in production is in proportion to the current production with a percentage increase of between 7–20% expected.

The optimal benefit from rbST is attained when management has put all possible measures in place regarding feed availability, health of cows, and other management factors. However, should uncontrollable factors limit feed availability, the cow cannot be harmed in terms of body condition or health while being treated with rbST. As reference data can show, cows do not lose body condition even when undergoing treatment, therefore, in the current challenging circumstances of the South African dairy industry, rbST will definitely improve profitability on the farm.


  • 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.

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

  • Chapula, W. and Galligan, D.T., 1989. Nutritional Implication of Somatropin for Lactating cows. Journal of Dairy Science 72:2510 – 2524.

  • Fike, J.H., Staples, C.R., Sollenberger, L.E., Moore, J.E. and Head, H.H., 2002. Southeastern Pasture-based Dairy systems: Housing, Posilac and supplemental silage effects on cow performance. Journal of Dairy Science 85: 866 - 878


Enquiries about rbST or Lactatropin: Please contact Frances Roos on 021 932 2019 or

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