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The Physicians Committee



Beyond Animal Research

By Jonathan Balcombe, Ph.D.
July 2005

Confining Rodents in Laboratory Cages Has Troubling Consequences

Throughout history, human societies have dealt with criminals by confining them in small cells. Not only does imprisonment remove the offender from daily life, but by taking away the inmate’s freedom and autonomy it constitutes punishment. Varying degrees of cutting off social contact represents a further penalty to the wrongdoer.

Animals caged in laboratories find themselves in comparable circumstances. From birth, rodents are confined in small, barren “shoebox” cages, usually stacked in an enclosed, windowless room. The only certain supplies are water, some bedding, and lumps of dull commercial food placed overhead where it can be only nibbled between the cage bars. Even these may not be available if a study protocol calls for deprivation. Any “environmental enrichment” typically amounts to a shelter and/or nesting material.

These conditions contrast starkly with those in the wild, where most home ranges are thousands of times larger and animals have opportunities to forage, burrow, climb, take cover, explore, nest, and choose compatible social partners. Recent research shows that both mice and rats bred for generations in the laboratory quickly revert to their ancestral behaviors when given the opportunity, and naturalistic housing would certainly be a great improvement to their welfare.

Standard laboratory settings also introduce undesirable intrusions. Rats and mice are highly sensitive to perturbations in their surroundings. They react stressfully to people entering the room, being picked up, and having their cages moved or cleaned.1

PCRM has been reviewing published studies of standard laboratory housing conditions in rodents. There is clear evidence that these animals perceive their conditions as undesirable with regard to spatial confinement, lack of stimulation and control, and social pressures. Here are just a few examples from our findings:

  • Mice presented with cages of various sizes made more visits to larger cages than to smaller cages, spending more time in them and working harder to gain access to them.2
  • Mice in standard cages drank more water containing an anti-anxiety drug than did mice given more resources (nest boxes, running-wheels, nesting material), indicating that depriving them of these resources is stressful.3
  • Rats living in larger-than-normal cages with stimulus objects still had smaller brains than did rats living in a large (81 cubic meter) outdoor enclosure.4
  • Rats spent four times longer in a more complex cage than in less complex cages.5
  • Rats lever pressed an average of 73 times for access to a standard cage containing three familiar rats.6
  • Enriched cages still represent confinement and an unnatural degree of temporal and spatial monotony. Several studies have reported behavioral stereotypies (functionless, repetitive behaviors that arise from the frustration of highly motivated behaviors) in animals kept in relatively “enriched” cages.7,8,9

Animals are not the only ones suffering from prison-like housing. Science suffers also. Trying to extrapolate from mouse to man is problematic enough, and there is evidence that standardized, shoebox housing makes it worse. Recent studies have documented an inability to replicate mouse studies between different labs, despite painstaking replication of animal strains and methods.10,11 Yet the scientific establishment remains largely unresponsive to this concern. Through a combination of economics and inertia, standardization remains the norm.

As long as rodents continue to languish in laboratory cages, prompt and substantive reforms are needed. Ultimately, however, we believe that both the animals and science will be better served when the cages are not larger, but empty.

Jonathan Balcombe, Ph.D., is a PCRM research consultant with a background in ethology. He is the author of The Use of Animals in Higher Education, as well as many scientific papers on humane life science education and animal behavior. His recent scientific review showing that animal experiments are more stressful than previously understood was published in Contemporary Topics in Laboratory Animal Science.

References
1. Balcombe JP, Barnard N, Sandusky C. Laboratory routines cause animal stress. Contemp Topics in Lab Anim Sci. 2004;43:42-51.
2. Sherwin CM, Nicol CJ. Behavioural demand functions of caged laboratory mice for additional space. Anim Behav. 1997;53:67-74.
3. Sherwin CM, Olsson IAS. Housing Conditions Affect Self-administration of Anxiolytic by Laboratory Mice. Anim Welf. 2004;13:33-39.
4. Rosenzweig MR, Bennett EL, Herbert M, Morimoto H. Social grouping cannot account for cerebral effects of enriched environments. Brain Res. 1978;153f:563-576.
5. Denny MS. The rat’s long-term preference for complexity in its environment. Anim Learning and Behav. 1975;3:245-249.
6. Patterson-Kane EG, Hunt M, Harper D. Rats demand social contact. Anim Welf. 2002;11:327-332.
7. Würbel H, Chapman R, Rutland C. Effect of feed and environmental enrichment on development of stereotypic wire-gnawing in laboratory mice. Appl Anim Behav Sci. 1998;60:69-81.
8. Powell SB, Newman HA, McDonald TA, Bugenhagen P, Lewis MH. Development of spontaneous stereotyped behavior in deer mice: Effects of early and late exposure to a more complex environment. Devel Psychobiol. 2000;37L:100-108.
9. Callard MD, Bursten SN, Price EO. Repetitive backflipping behavior in captive roof rats (Rattus rattus) and the effects of cage enrichment. Anim Welf. 2000;9:139-152.
10. Crabbe JC, Wahlsten D, Dudek BC. Genetics of mouse behavior: Interactions with laboratory environment. Science. 1999;284:1670-1672.
11. Chesler EJ, Wilson SG, Lariviere WR, Rodriguez-Zas SL, Mogil JS. Identification and ranking of genetic and laboratory environment factors influencing a behavioral trait, thermal nociception, via computational analysis of a large data archive. Neurosci and Biobehav Rev. 2002;26:907-923.

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