Parliamentary Research Branch


PRB 98-1E


Prepared by:
Frédéric Forge
Science and Technology Division
October 1998

Bovine somatotropin (bST), which is also called bovine growth hormone, is a natural hormone produced in the pituitary glands of cattle, which stimulates growth in calves and lactation in adult cows. A relationship has been found between the quantity of bST present in cows and their milk production.

The hormone bST, which is present in milk, is, like any other protein, broken down in the digestion process. It is also destroyed to a large extent by pasteurization.

Until the 1980s, the only means of obtaining rbST was to produce an extract from the pituitary glands of dead animals -- just as the insulin required by individuals suffering from diabetes was originally taken from the pancreas of human cadavers. However, the limited amounts of the product obtained in this way and its impurity meant that it could never be used commercially.

Recombinant bovine somatotropin (rbST) is simply bST produced "outside the animal." The gene that expresses bST is inserted into a bacterium using the recombinant DNA technique.(1) This bacterium can then produce a hormone identical to bST, which is called rbST. This process, which is the same as that used to produce insulin, makes it possible to obtain large quantities of a very pure product.

When the diet of lactating cows is supplemented with rbST, as a veterinary medication, milk production can be increased by between 10 and 15%; however, the cows’ appetite is also stimulated and they have to eat more in order to support this increased production.

The rbST produced by pharmaceutical companies differs only very slightly from naturally occurring bovine somatotropin. Although it is possible in theory to detect the presence of rbST in cattle, it is very difficult to do so in practice. At the present time there is no practical method of testing for its presence in milk or blood serum, either directly or indirectly.

(1) The recombinant DNA technique involves the manipulation of genetic material (DNA or deoxyribonucleic acid) and can be used, for example, to transfer genes from one species to another in order to create transgenic hybrids of plants, animals or micro-organisms.