Part 3.2 Animal enclosures

This is Part 3.2 of the Code of Practice for the Housing and Care of Laboratory Mice, Rats, Guinea Pigs and Rabbits.

The design of animal housing should facilitate well being of the animals, meet research requirements, minimise experimental variables, and isolate the animals from wide variations in temperature and humidity and from vibration and sources of loud noise.

For detailed requirements of the design of animal rooms, refer to 'Housing for Laboratory Rats, Mice, Guinea Pigs and Rabbits', A.L. Hargreaves, ANZCCART 2000. Consideration should also be given to occupational health and safety requirements when designing animal housing.

The formation of social groups, and utilisation of enrichment devices and bedding material to enable climbing, burrowing, nesting, reproduction and thermoregulation are as important as provision of adequate cage space for these species.

Mice, rats and guinea pigs tend to avoid open spaces.

Mice

Mice, in particular, like to compartmentalise their behaviours and often use urine marking and bedding to assist.

Rats

Rats enjoy standing on their hind legs and peering from their enclosures. They are excellent climbers, utilising the full height of their housing, and also use urine spotting as a territorial marker.

Guinea pigs

Guinea pigs are timid, social animals and can be slow to adapt to change in their environment. As these animals have a poorly developed capability for either jumping or climbing, they may be housed in a relatively low walled, open topped pen or cage. Natural behaviours include stampeding which may be avoided by providing sheltered or hiding places, and avoiding sudden noise, disturbance or overcrowding.

Rabbits

There is a need to provide enough space to permit rabbits to meet their species-specific needs. This includes sufficient exercise for skeletal development (hopping, rearing up) and direct social contact with other compatible rabbits. Rabbits can be housed in cages or floor pens. Pens are enclosures that allow for greater freedom of movement and expression of social behaviours. Cages are fully enclosed containers that may restrict freedom of movement and social interaction because of their size and possibly design. The advantages and disadvantages of housing rabbits in cages versus pens are discussed comprehensively in the 'Guidelines for the Housing of Rabbits in Scientific Institutions' developed by the NSW Animal Research Review Panel (see Section 4). These guidelines recommend the use of pens for housing laboratory rabbits.

Minimum standards for animal enclosures in general:

1. Animal enclosures (cage or pen) must meet or exceed the minimal space requirements outlined in this Code to permit reasonable freedom of movement and normal postural adjustments.
2. Enclosures must be compatible with what is known of the behavioural and physiological needs of the animals.
3. Enclosures must be durable and provide a comfortable environment, be maintained in good repair, be kept clean and be escape-proof.
4. Enclosures must confine animals safely with easy access to food, water and ventilation and enable easy monitoring and access to the animals.

General recommendations:

1. Size, design and materials used in the construction of animal enclosures may affect many of the environmental factors normally controlled at room level and thus may affect the characteristics of the microenvironment. Refer to Section 3.3 for recommendations concerning climate control.
2. Special containment facilities are required for the use of radioisotopes, infectious agents and highly toxic substances. For specific requirements and recommendations, refer to appropriate guidelines.

3.2.1 Materials and design of animal enclosures

The different materials used for animal enclosures affect shading and social contact via degree of transparency, as well as heat and noise conduction.

Although mesh or wire floor cages may offer some advantages over solid floor cages, for example to reduce disturbance during cleaning and to reduce the risk of cage flooding, solid floors provide a more comfortable and insulated surface with a reduction of the risk of injury. Faulty mesh or wire floors and lids can lead to serious injuries.

The design of housing, whether enclosed, such as 'shoebox-style' cages, or open-type designs such as pens, determine the air movement and rate of dissipation of heat. Filter tops exacerbate the effects on ventilation of an enclosed design. They raise the temperature and relative humidity inside the cage and hasten the build-up of carbon dioxide and ammonia.

Minimum standards for materials and design of animal enclosures:

1. Enclosures must be designed and made of materials that are comfortable and safe for the animals, and withstand cleaning agents and techniques.
2. Housing must enable easy monitoring of the animals.
3. Nesting boxes (or equivalent) must be provided for breeding animals.
4. Wire or mesh floors and lids must be carefully selected and maintained to minimise the risk of foot and leg injuries. A solid mat or suitable substrate must be provided.
5. Insect vectors of myxomatosis and calicivirus rabbit disease (flies and mosquitos) must be prevented from entering rabbit enclosures.

General recommendations:

1. Ventilated racks and IVCs used to house laboratory rodents provide separation at the rack and cage level, respectively. Consideration should be given to the additional heat load, noise and draughts provided by these systems. Separation of the motorised components of such systems reduces noise and heat impacts.
2. In the design of animal enclosures, consideration should be given to make the housing environment suitably complex or enriched (see also Section 3.4).

Species specific recommendations

Mice:

1. Wire lids for mouse cages should be carefully selected to prevent toe injuries

Rats:

1. Galvanised metal should be avoided in the long term for rats, due to excessive risk of zinc toxicity.

Rabbits:

The 'Guidelines for the Housing of Rabbits in Scientific Institutions' (see Section 4.) is recommended for principles of rabbit pen design. Provision for rabbits to withdraw from others should be provided, and subdivision to facilitate cleaning and catching animals in pens is recommended.

3.2.2 Space requirements

For all species, it is recognised that social relationships, enclosure shape and internal furnishings may be as important to the animal as overall size of the enclosure. The shape of the cage or floor pen may contribute to the security and comfort of the animals.

Guinea pigs

Guinea pigs prefer to lie down and stretch out and also to congregate around the periphery of the enclosure. An elongated shape maximises the length of space and wall for the occupants and reduces the central more exposed space. Guinea pigs do not readily climb, and can be housed in open topped pens or cages. They do sometimes stand up and should be provided with adequate height to do so.

Rabbits

Rabbits like to lie down outstretched. They often stand upright, hop or play, which is essential for normal skeletal and social development.

Minimum standards for space requirements:

1. Adequate space must be provided to allow animals to exercise, to maintain the social stability of the group and to perform normal physiological and behavioural activities.
2. Stocking densities must be adjusted for different breeds, ages and growth of the animals.
3. The details of space requirements are given in Appendix 1, where the stated dimensions refer to internal measurements of the animal enclosure. Animal housing must comply with these dimensions with the exception of short-term housing of animals post-weaning and prior to issue, provided there are no associated deficits in their welfare.
4. All four species either climb or assume upright posture at times, which must be accommodated without hindrance by the height of the enclosure.

3.2.3 Social requirements

The way in which the cage or pen is stocked has direct social and welfare consequences for the animals. Single housing will cause social deprivation and impacts on the animal's capacity to thermoregulate.

Intense territoriality may be seen in reproductively active male animals. Castration prior to puberty may prevent aggression and fighting. Pregnant and lactating females may prove aggressive in nest defence. Some strains of rodents are more aggressive than others, which results in fighting within groups.

Minimum standard for social requirements:

1. Animals must be housed in social groups unless the welfare of the animal would be compromised by group housing.

General recommendations:

1. Stocking density should permit animals in a group to disperse or withdraw comfortably and establish natural hierarchies within the group. It is then recommended to keep the composition of the group stable.
2. The composition of the group with regard to sex, age, temperament and familiarity should be considered when housing animals. Animals displaying aggression toward one another should be separated.
3. Where single housing is justified on welfare grounds or as part of an experimental protocol, consideration should be given to the provision of environmental enrichment and social contact through visual and auditory contact, wherever possible. This will help to avoid isolation stress, which may result in increases in nervousness, aggression, and susceptibility to convulsions, certain drugs and metabolic and adrenocortical activity.

Species specific recommendations

Mice and rats:

1. Wean animals into social groups to prevent fighting and to create stable, manageable hierarchies.

Guinea pigs:

1. Guinea pigs are social animals and prefer to live in groups of 5 to 10 animals. They should be kept in compatible groups or breeding pairs or harems. Breeding groups of 3 to 10 males and 15 to 30 females can also be managed, by allowing a social group to increase naturally thus evolving a social hierarchy or by adding new females. Females can usually be housed together even if strangers. Males can be kept in groups up to 4 months and then need to be in pairs. Adult males can fight, especially in the presence of an oestrus female.

Rabbits:

1. Group housing should be provided for rabbits. It should include the opportunity for the animals to rest and withdraw from each other.
2. Wherever possible littermates should be housed in groups post-weaning.
3. Uncastrated mature male rabbits (over 12 to 14 weeks of age) should not be housed together. Castration prior to puberty (before 12 to 14 weeks) is recommended, where appropriate, to prevent intolerance and fighting amongst sexually mature males.
4. Rabbits that cannot be housed in groups (destabilised hierarchies, intact males or those involved in AEC approved experimental protocols) should have extensive olfactory and visual contact with other rabbits, as well as the ability to withdraw.

3.2.4 Bedding and nesting

Minimum standards for bedding and nesting:

1. Bedding material appropriate to the species must be provided in animal enclosures with solid flooring.
2. Nesting material must be provided for breeding animals.
3. The nesting area for rabbits must be designed to allow the doe to exhibit normal nesting behaviour and contain the young rabbits in the early post-partum period, with sufficient size to permit suckling. In addition, breeding does must be provided with adequate nesting material at least five days before parturition until the litter is weaned.
4. Bedding and nesting materials must be comfortable and safe for the young and adults, dry, absorbent, dust-free, low-allergenic, non-toxic, non-injurious and free from vermin and other contaminants.

Species specific recommendations

Mice and rats:

1. Materials likely to entangle rats and mice should not be used as permanent bedding.

Guinea pigs:

1. Guinea pigs do not build nests but require some form of bedding to provide cover for young and burrowing for general environmental comfort and enrichment. Recommended examples of suitable bedding material for guinea pigs include low-dust wood shavings (not sawdust as this may adhere to the preputial area of males), shredded paper or hay.

Rabbits:

1. Recommended types of bedding or nesting material for rabbits that may be used alone or in combination include straw, shredded paper and non-toxic wood.

3.2.5 Special requirements of animal enclosures

Minimum standards for special requirements of animal enclosures:

1. Animal house personnel and investigators must be aware of any special requirements of animals involved in experimental protocols, which must be documented in the experimental protocol. Such animals must be identified and records kept of close monitoring for signs of distress or discomfort, particularly if they are transferred between facilities with different housing conditions.
2. The special care and housing requirements of albino, genetically modified, cloned, aged, immunocompromised animals must be provided. Similarly, animals that have been affected by disease, surgery or pharmacological compounds may have particular social, dietary or behavioural characteristics that must be considered.
3. Where microbiological barrier conditions are in place for biocontainment or bioexclusion, steps must be taken to provide a complex cage environment and to allow interactions with animal care staff to meet the needs of the animals.

Mice and rats:

1. In addition to a lack of fur for thermoregulation, nude mice and rats do not have eyelashes for protection of the eye and eyes and skin can easily become irritated by bedding fibre. It is recommended that low-dust bedding and nesting material be used for these strains.