While it is impossible to determine the precise number of animals used in research—as there are no reporting requirements for mice and rats, who make up the majority of animals used (95 to 97%)—several reliable estimates are available.
Worldwide, an estimated 192.1 million animals are used every year for scientific purposes.(1) Of this figure, roughly 100 million are used annually in the United States, including at least 25-35 million vertebrate animals and at least 1.5 million in Massachusetts. The most common species used in research are mice, rats, rabbits, guinea pigs, hamsters, farm animals such as sheep and pigs, dogs, primates, and cats (listed from most to least often used).
(1) “Research” and “scientific purposes” refer to the use of animals for research, testing, teaching, experimentation, and/or surgery, as well as animals bred for research but not used.