Archive -- New Developments in Genetic Engineering of Dairy Cattle

In an example of how the cloning process works, researchers collect cells from a 30-day-od bovine embryo and grow the cells in a laboratory incubator (cell culture). The nucleus (which contains the genetic information) from a single cell is injected into tan unfertilized bovine egg (nuclear transfer). The resulting embryo will undergo cell divisions to produce an embryo that appears normal, but it may fail to develop after embryo transfer to the reproductive tract of a cow. Researchers have learned that development to term can be improved if cells from the nuclear-transfer embryo are made to undergo a second nuclear transfer procedure. This second nuclear-transfer embryo will develop to term.

Through generations of careful selection and breeding, animal breeders have succeeded in building the high quality and production of today's dairy cattle. While they continue to improve the genetic potential of dairy cattle through these traditional means, genetic engineering, through in early stages of development, holds promise of a new approach to breeding. Transgenic technology and cloning by nuclear transfer are two such techniques.

Transgenic technology, which involves transferring foreign genes into an animal, is widely used in biomedical reseat with laboratory mice. But for reasons that are not fully understood, cattle appear to be less likely to integrate a foreign gene than other large animals, which in turn have less success than laboratory mice.

Low success rates combined with the high costs of maintaining cattle, the long intervals between generations, and the small number of offspring, have made trangenic reseat with cattle extremely expensive, which limits the number of laboratories woldwide equipped to conduct the research.

As a result, large research programs are being supported primarily by private pharmaceutical companies with the aim of producing transgenic cattle that secrete high-value proteins (e.g., pharmaceutical compounds used to treat human disease) in their milk. For example, the goal of one east coast company is to capture the market for human infant formula by trying to produce transgenic cattle whose milk contains an important protein found in human breast milk.

While pharmaceutical companies are exploring trangenic technology for commercial purposes, animal science researchers at U.C., Davis, are focused on developing the technology to advance the dairy industry.

Specifically, we are investigating whether fore9ign genes inserted into dairy cattle can change the manufacturing or nutritional properties of milk. We have succeeded in demonstration with transgenic mice that foreign genes can be expressed by the mammary gland to modify milk components. However, we have met the same obstacles as industrial scientists in trying to produce similar results in transgenic cattle. It appears that what we need is a significant breakthrough to improve the efficiency and reduce the cost of aiming transgenic cattle.

Cloning by nuclear transfer is another method of genetic engineering still in experimental stages. Despite all the media reports, the purpose behind experiments leading to the creation of "Dolly", the sheep made famous through cloning, was not to make multiple copies of a single animal. Rather, researchers were interested in finding cell types that could be used to generate a normal animal after transfer of a cell's nucleus into a recently ovulated egg, a process known as nuclear transfer. The ultimate goal of this cloning research is to produce animals from cells that have been genetically modified in the laboratory, or in other words, to produce transgenic animals from transgenic cells.

The advantage of this approach is that cultured cells can be modified and selected in the laboratory and then allowed to develop into a trangenic animal, instead of relying on the small number of transgenic offspring produce by injection DNA into embryos.

At U.C.Davis, we have begun research aimed a developing embryonic cells lines that can be used to produce trangenic dairy cattle by nuclear transfer. We believe that our cell lines will offer certain advantages over those currently being tested by other laboratories.

Gary Anderson is a professor in the Department of Animal Science at U.C. Davis. He was recently honored a s a "Teacher of the Year" at the university.