Transgenic Animals
Given the commercial success of transgenic plants, the lack of commercially available transgenic animals is surprising. There are several reasons for this. Many crops had readily identifiable problems (eg. corn and the European corn borer) that could be attacked with single genes (eg. gene that produces a protein that is toxic to the borer). Such simple problems are less common in animal production systems. For example, feed efficiency (the ability of an animal to convert feed into tissue) is tremendously important; if an animal can gain weight with less feed, the producer can reap large savings. Unfortunetely, a number of factors control feed efficiency, and single-gene solutions are unlikely. Increased animal (eg. pig) growth hormone improves feed efficiency but can also seriously affect animal health (eg. abnormal skeleton development).
Fish are an exception. Transgenic Salmon with boosted levels of growth hormone grow substantially faster than their non-recombinant counterparts, apparently without major side effects. However, environmental concerns are substantial; transgenic fish would be raised in aquaculture and in such systems it is difficult to prevent occasional escapes into the environment. Escaped fish could then interbreed with wild salmon populations, possibly resulting in decreased levels of overall fitness. Transgenic fish are usually sterile; thus escaping fish would be unable to breed with wild fish. Despite this protective feature, the release of transgenic fish remains a contentious issue.
The highly publicized success of Scottish researchers in producing an adult clone of a sheep (‘Dolly’) has focused attention on the possibility of using transgenic animals to produce human proteins in sheep. Such proteins (eg. ?1-antitrypsin) have therapeutic uses.This ‘molecular pharming’ will probably be the first commercial use of transgenic farm animals; it is debatable whether such use of animals is either a ‘food’ or ‘agriculture’. Nonetheless, the success or failure of molecular pharming in animals will have important reverberations on the development of transgenic animals with more conventional agricultural uses.
