PRB 98-1E
WHAT IS rbST?
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. |