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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