SCIENCE / Animal Farm in the Nineties laboratory

Ethical constraints that hold back research on the genetics of humans have not all been applied on work with animals. Scientists have manipulated the genes and embryos of animals to create living organisms that would not occur naturally. The range of possibilities appears to be endless; from farm animals that produce valuable pharmaceutical remedies in their milk to laboratory mice that are genetically programmed to develop human diseases for which there are no cures.

One important development from the discovery of genes responsible for human disorders has been the creation of laboratory animals with the same diseases. By inserting the defective human gene into the embryos of mice, for instance, scientists have been able to produce 'transgenic' animals that show many of the symptoms of the human condition. Medical researchers say they need such animals to get a better understanding of the human disease and to find cures by testing new drugs and treatments that can alleviate the symptoms of their laboratory 'model'.

Already, scientists have developed transgenic mice with the defective human cystic fibrosis gene. The creation of so-called knock- out mice is well developed for a range of other diseases, such as sickle-cell anaemia and atherosclerosis, which causes heart disease. The most celebrated transgenic mouse, however, is one that has been genetically manipulated to develop cancer within a few weeks of birth. Owners of the patent on Oncomouse, the trade name of the animal, expect to earn a small fortune from licensing it to cancer workers researching a cure for the many different forms of the disease.

Photographs published in 1982 of the first transgenic animal, a mouse which grew nearly twice as big as its litter-mates because it had a gene for rat growth hormone inserted into it while an embryo, illustrated the power of the new biology. They also made some critics feel uneasy. Commercial exploitation of these animals raised even more questions. Why should it be possible to patent an animal, especially one that has been designed to suffer?

Advocates argue that the suffering of the animal is more than outweighed by the benefits of alleviating human suffering. The argument is easier to sustain, of course, when there is little or no suffering for the animal and the potential human benefits are considerable. Scientists, for instance, have created transgenic sheep that can produce human proteins in their milk. The animals look exactly like normal sheep, except they can produce a vital drug - the human protein - for people suffering from emphysema, which causes breathlessness. Most people would approve of this experiment.

However, there are a few examples of scientists making grave mistakes in the genetic engineering of animals. Agricultural researchers in the US, for instance, inserted genes for human growth hormone into pigs in an attempt to produce leaner meat in animals that grew bigger. The result was the 'Beltsville pig' (named after the town in Maryland where the research centre is based), which suffered severe arthritis and could not stand.

British researchers say such an experiment, which at the time was undertaken with little knowledge of the consequences, would not be approved in the UK. Here every research project has to be licensed and the likely scientific benefits are set against possible animal suffering. But, as with many ethical problems, different people will define necessary and acceptable suffering differently.