That guinea pigs have become shorthand for an experimental subject is no coincidence. The furry creatures have been used in experiments for centuries, hence the dismay this week that a Staffordshire farm has decided to stop breeding them after years of intimidation by activists. Staff at the Darley Oaks farm have received death threats and the body of a relative of the family that owns the business was stolen from a churchyard.

"Guinea pigs have provided essential information to support biomedical research into respiratory disease resulting in real breakthroughs in the development of new medicines," says Philip Wright, director of science and technology at the Association of the British Pharmaceutical Industry.

The Spanish brought guinea pigs to Europe from South America 400 years ago. Scientists realised they had biological similarities to humans that would make them useful in many fields. The German scientist Robert Koch used the animals to discover that TB was caused by Mycobacterium tuberculosis in 1882, and researchers have not looked back since. Their sensitivity to TB and other infections, and the similarities of their immune system to that of humans, have made them important in the study of other diseases.

In 1907, vitamin C was discovered using guinea pigs (like humans they cannot produce the vitamin and need it supplied in their diet) and they have since contributed to 23 Nobel prizes for medicine or physiology. Guinea pig studies led to the discovery of the hormone adrenaline and helped develop replacement heart valves, blood transfusions, antibiotics and asthma medicines, as well as vaccines for diptheria and TB. They were used in over 45,000 scientific experiments in the UK in 2002, 1.7% of all research using animals.

Current projects include efforts to understand hearing disorders (guinea pigs have a similar ear structure to humans) and work on allergies, including anaphylactic shock, and respiratory diseases. The animals have airways that are very sensitive to allergens. They have also been recruited to test new vaccines against anthrax.