[1][2] Currently, rodents are commonly used in animal testing for physiological, pathological and behavioral scientific studies, particularly mice and rats, but also guinea pigs, hamsters, gerbils and others.
The total number of animals for those organizations is: 250,000–1,000,000 rats; 400,000–2,000,000 mice; and 130,000–900,000 birds.Mice are the most commonly used vertebrate species, popular because of their availability, size, low cost, ease of handling, and fast reproduction rate.
[10] Chimeric mouse production consists of injecting embryonic stem cells provided by the investigator into 150–175 blastocysts, representing three days of work.
[15] For example, the utility of the use of rodents in testing for sepsis,[16][17] burns,[17] inflammation,[17] stroke,[18][19] ALS,[20][21][22] Alzheimer's,[23] diabetes,[24][25] cancer,[26][27][28][29][30] multiple sclerosis,[31] Parkinson's disease[31] and other illnesses has been called into question by a number of researchers.
Regarding experiments on mice in particular, some researchers have complained that "years and billions of dollars have been wasted following false leads" as a result of a preoccupation with the use of these animals in studies.
Moreover, persistent virus infections (for example, herpesviruses) are activated in humans, but not in SPF mice, with septic complications and may change the resistance to bacterial coinfections.
[19] For example, researchers have found that many rats and mice in laboratories are obese from excess food and minimal exercise which alters their physiology and drug metabolism.
[32] Many laboratory animals, including mice and rats, are chronically stressed which can also negatively affect research outcomes and the ability to accurately extrapolate findings to humans.
[19][21][22] One explanation for deficiencies in studies of rodents housed in laboratory cages is that they lack access to environmental agency and thus the ongoing freedom to make decisions and experience their consequences.
Examples of hidden bias include a 2014 study from McGill University in Montreal, Canada, which suggests that mice handled by men rather than women showed higher stress levels.