TRANSGENIC DAIRY-CATTLE - GENETIC-ENGINEERING ON A LARGE-SCALE

Amid the explosion of fundamental knowledge generated from transgenic animal models, a small group of scientists has been producing transgen ic livestock with goals of improving animal production efficiency and generating new products. The ability to modify mammary-specific genes provides an opportunity to pursue several distinctly different avenues of research. The objective of the emerging gene ''pharming'' industry is to produce pharmaceuticals for treating human diseases. It is argu ed that mammary glands are an ideal site for producing complex bioacti ve proteins that can be cost effectively harvested and purified. Conse quently, during the past decade, approximately a dozen companies have been created to capture the US market for pharmaceuticals produced fro m transgenic bioreactors estimated at $3 billion annually. Several pro ducts produced in this way are now in human clinical trials. Another r esearch direction, which has been widely discussed but has received le ss attention in the laboratory is genetic engineering of the bovine ma mmary gland to alter the composition of milk destined for human consum ption. Proposals include increasing or altering endogenous proteins, d ecreasing fat, and altering milk composition to resemble that of human milk. Initial studies using transgenic mice to investigate the feasib ility of enhancing manufacturing properties of milk have been encourag ing. The potential profitability of gene ''pharming'' seems clear, as do the benefits of transgenic cows producing milk that has been optimi zed for food products. To take full advantage of enhanced milk, it may be desirable to restructure the method by which dairy producers are c ompensated. However, the cost of producing functional transgenic cattl e will remain a severe limitation to realizing the potential of transg enic cattle until inefficiencies of transgenic technology are overcome . These inefficiencies include low rates of gene integration, poor emb ryo survival, and unpredictable transgene behavior.