Nigel Pelvin, of King's High School, asks :-

Why are rats used in most experiments?

John Schofield, of Lab Animal Sciences at Otago University, responded.

Rats are frequently used because they are inexpensive, easy to care for, easy to handle, grow quickly and we know a lot about them.

The laboratory rat, Rattus norvegicus, was the first mammalian species to be domesticated for scientific purposes. The earliest research on the rat occurred around 1850 when they were used for nutritional studies. Many of the strains of rats used in research today were developed at the Wistar Institute in Philadelphia (USA). Scientists there realised that the nervous system of a rat grew in the same manner as in humans but 30 times faster. For example a 3-year-old rat is equivalent to a 90-year-old human.

Large numbers of rats can be bred and maintained under disease-free conditions in specialized climate-controlled facilities. A rat costs $20 and 20c per day to keep, cheap compared to a monkey at 2000 and $5. Over the years a great deal of information has been learned of the biology of a rat. Some 200 unique strains (inbred) have been developed, each strain having, for example, quite different types and rates of cancer. A unique feature of a particular inbred strain is that all rats are identical copies of each other. Thus a wide range of human health problems may be studied without genetic variability confusing the results. For example the transplantation of tissues, such as kidney transplants, can readily be studied using a pair of inbred rats because organ rejection does not occur. Because rats cannot vomit (their stomach anatomy prevents this) they are an ideal model for testing the toxicity of any new drugs prior to testing on humans.

Rats and mice represent about 80-90per cent of all animals used internationally in biomedical research and testing. In New Zealand they represent only 33 per cent because here 50 per cent of all animals used are domestic farm species used in agricultural and veterinary research.