Modifications to Husbandry and Housing Conditions of Laboratory Rodents for Improved Well-being

Citation: Smith AL, Corrow DJ. Modifications to husbandry and housing conditions of laboratory rodents for improved well-being. ILAR J. 2005; 46(2):140-7.

Location: The public is allowed to view this entire article online for free here.

Favorite line: “It must be remembered that well-being can be improved only if the normal behavior and physiology of the animals are understood.”

Official abstract: For a change to be considered enriching, the change must enhance animal welfare and improve biological functioning of the animals. A review of the literature shows that a consensus on the definition of changes constituting “environmental enrichment” has yet to be reached. For this reason, the results of studies on the effects of rodent enrichment are inconsistent. In many cases, changes have not been shown to be real improvements. However, enrichment is increasingly appreciated as a way to improve the well-being of rodents, providing them with opportunities for species-specific behaviors that might be available to them in the wild. Frequently defined as “change to the environment,” enrichment can be as complex as devices (frequently termed “toys”) or as simple as the provision of tissues from which mice readily construct nests. Nest making is a learned behavior in rats, and laboratory rats do show preferences for chewable objects in their environment. Rather than attempting a comprehensive review of the entire literature on environmental enrichment and its effects on rodent physiology and behavior, this paper focuses on husbandry and housing alterations that may improve the welfare of laboratory rodents. The effects of beneficial changes in housing and husbandry on rodent well-being and on experimental variability–and thus cost–are discussed. Areas that require more research are suggested. Also suggested are possible inexpensive and effective enrichment schemes for laboratory mice that might include reducing the cage floor space per mouse combined with providing nesting material.  Key words: enrichment; housing; husbandry; mice; rats; rodents.

Rattery-relevant summary:


“Modifications…” is a review paper of rodent enrichment.  In scientific literature, rodent enrichment is often categorized into devices (toys), social grouping, nesting materials and handling. Any change to an animal’s environment should increase positive and normal species-specific behaviors, decrease the occurrence of abnormal behavior, and increase the animal’s ability to cope with captivity. Changing an animal’s environment just for change does not necessarily have a positive impact on welfare and is not considered enrichment.


In one study, mice given enriched cages maintained a single potty area and slept with a close buddy, while those in standard cages urinated all over and slept in large groups.  Some people may hypothesize that providing places to hide will make shy animal harder to catch and more resistant to human handling. However, some studies have found that providing enrichment decreases fear responses to humans, perhaps because the animals feel more secure.

Several studies noted mice kept in enriched cages attacked intruders and were more hostile to cage mates than those in standard cages. The position of the dominant male is less stable in enriched cages. This increased aggression and decrease in hierarchy stability led to an increased susceptibility to getting sick. In terms of group size, the lowest levels of aggression were noted in groups of three to five kept in areas of small floor space. Several studies noted that aggression in mice actually increased with more floor space – decreased floor space means less defendable territory; however, these cages were not enriched with any objects.

Female mice prepare nests even when not in breeding condition, as do males, so providing nesting material to mice at all times may be an efficient way to enrich their lives. Roughly 97% of mice provided with nesting material will build a nest within the first night. Building a nest provides mice with a hiding place and helps the animals’ temperature regulation. In terms of material preference, tissues or paper towels were preferred over paper strips and wood products. Mice will work for access to any nesting material, and placing it on the top of a cage will encourage this.


There are conflicting studies about stress levels in rats given enrichment. Some find stress hormone levels lower when rats are given toys, other find them higher when given enriched cages.  A preference for chewable enrichment items was observed over choices of hiding places and toys.

Nest-building in rats is a learned behavior, and rats should be exposed to nesting material before 8 weeks of age. If not, they may eat more of the material, build simpler nests, and soil their finished nests more than those exposed at an early age.

By housing rats in groups of two to four, stress can be reduced from that of a rat housed alone.

Enrichment Variables

Providing enrichment can increase variability between animals in multiple areas. One such example is a reduction in the number of pups born to mice provided with enrichment. Areas with variability are also different in assorted strains and sexes.

%d bloggers like this: