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Species
Listed in descending order of numbers of individal animals used:
Invertebrates
The greatest number of animals used for animal testing are the invertebrates, Drosophila melanogaster and Caenorhabditis elegans. This is in part because of the short generation time of under a week, and in the case of C. elegans details being known about the precise lineage of all of the organisms cells. However, with the exception of some cephalopods, invertebrate species are not protected under most animal research legislation, and therefore the total number of invertebrates used remains unknown.
Rodents
Rats and mice, the most commonly utilized vertebrate species, are used in large proportion because they are small, inexpensive, easy to handle and care for, and can produce up to 100 pups in a year. Mice are considered the prime model of inherited human disease, are genetically tractable and share 99% of their genes with humans. [47] In the UK, 1,910,110 mice were used in 2004. In the U.S., the numbers of rats and mice used are not reported, but are estimated at 15-20 million.
Fish and Amphibia
In the UK, 194,562 fish and 18,195 amphibia were used in 2004 [49] (pdf). The major species utilized are the zebrafish, Danio rerio, which are translucent during their embryonic stage, and the African clawed frog, Xenopus laevis.
Rabbits
Over 20,000 rabbits were used for animal testing in the UK in 2004. Albino rabbits are used in eye irritancy tests because they have less tear flow than other animals. They are also used in skin irritancy tests (see Draize test). In 2004 less than 12% of the rabbits were used for safety testing of non-medical products.
Dogs
Beagles are used, because they are friendly and gentle, in toxicity tests, surgery, and dental experiments. Toxicology tests are required to last six months in the UK, although British laboratories carry out tests lasting nine months on behalf of Japanese and American customers. In the UK, most dogs are bred for the purpose, for example by Harlan in Leicestershire. Of the 5,570 dogs used in the UK in 2004, 5,476 were purpose-bred.
Non-human primates
In the United States, 54,998 non-human primates were used in 2004, according to the U.S. Department of Agriculture, an annual figure that has been more or less steady since 1973 [52] (pdf, p. 10). In the European Union, 10,000 are used each year, with 4,208 used in Britain in 2004, a decrease of 591 from the previous year. Most of the NHPs used are baboons, macaques, marmosets, and chimpanzees. The use of great apes, also known as Hominidae — humans, gorillas, chimpanzees, and orangutans — is prohibited in Britain, but chimpanzees are still used in the U.S., with an estimated 1,300 in use at any given time, according to the Humane Society of the United States.
Cats
In the UK, 819 cats were used in 2004




