Housing

Aspects of best practice

• Social housing in large, stable social groups with visual and auditory access to neighbouring groups allows performance of a full range of natural behaviours.
• A grassed outdoor area with indoor shelter is cheaper and less time consuming to construct and maintain than solid housing.
• A large area with visual barriers and climbing structures at vertical, horizontal and diagonal angles provides choice and complexity, opportunity for physical exercise and room to avoid, flee or hide from dominant animals.
• High, wide, perches allow animals to view inside and outside of the enclosure [6,7].
• Grass into which seeds and grains may be thrown to provide foraging opportunities, The corral also contains naturally occurring herbs, other plants and invertebrates. Macaques housed in outdoor pens with grass substrate spend more time foraging and less time fighting than macaques housed in outdoor pens with gravel substrate [8,9].
• Soft ground causes less wear and tear on joints than does concrete or gravel.
• Natural sunlight enhances vitamin D levels and bone strength.
• Areas of shade and indoor areas allow animals to regulate their body temperature by avoiding extremes of weather. Macaques spend a significant proportion of their day basking in the sun and resting in the shade [10,11].
• Less staff time is spent cleaning organic waste matter or distributing enrichment devices as animals can express naturalistic time budgets, foraging resting, grooming and locomoting.
• Suitable enrichments for group housed animals are relatively cheap, quick and easy to provide.
• Spreading odours around the enclosure, including less visited areas, encourages exploratory and locomotory behaviour.
• Socially housed animals provide research opportunities for scientific programmes incorporating social aspects.

Considerations

• Enclosure structures must provide complex climbing and other locomotory opportunities, be sturdy, well built and maintained regularly.
• Where possible, enclosure furniture should be made from organic ‘warm’ materials, such as wood [2].
• Fencing must be storm-proof and there must be no opportunity for escape.
• There must be multiple areas where animals may seek warmth, or cool down, so that all animals may regulate their body temperature.
• Valued resources should be spread out around the enclosure, so that subordinates can gain access.

The two-tiered housing above has a wooden slatted floor between the two levels, increasing the available surface area and creating an additional visual barrier. The fencing and roofing provide climbing structures in addition to the vertical, horizontal and diagonal structures/perches inside. There are multiple access points (‘pop holes’) between the two levels to prevent dominant animals from monopolising them, and ladders, steps and platforms to aid young and geriatric animals to reach them. For more information, see Waitt et al. 2008.

Aspects of best practice

• Social housing in medium- to large-sized, stable social groups with visual and auditory access to neighbouring groups allows performance of a full range of natural behaviours.
• Visual barriers and climbing structures at vertical, horizontal and diagonal angles provides choice and complexity, opportunity for physical exercise and room to avoid, flee or hide from dominant animals.
• Multiple access points enable all animals to access resources such as feeders, water spouts and resting areas.
• Less staff time is needed for making and distributing enrichment devices. Suitable enrichments for group housed animals are cheap, quick and easy to provide.
• Scattered foods encourage exploratory and foraging behaviours.
• Natural sunlight and fresh air reach the lower level due to the mesh sides and slatted floor.
• Areas of shade allow animals to regulate their body temperature by avoiding extremes of weather. Macaques spend a significant proportion of their day basking in the sun and resting in the shade [10,11].
• Socially housed animals provide research opportunities for scientific programmes incorporating social aspects.

Considerations

• The outer fittings as well as the internal substrates and environmental enrichment should be sturdy and well-constructed, as the macaques are likely to bounce off the mesh as well as shake it and try to pry joined pieces apart.
• Mesh must be sturdy and well maintained. Sand down sharp edges and fix loose connections and broken wires immediately.
• Wherever possible use softer natural materials such as wood. Metal caging is noisy, which can cause stress for both animals and staff.
• Staff must add and remove foraging substrate and organic waste matter from the floor.
• Concrete flooring is hard on the animals’ joints.
• Avoid drainage systems which could become easily clogged.

The image above shows a complex and stimulating space, large enough for macaques to run, climb, swing, jump, flee upwards and hide from dominant animals or humans (Credit: MRC Centre for Macaques).

Aspects of best practice

• Social housing in medium-sized, stable social groups with visual and auditory access to neighbouring groups allows a range of natural behaviours.
• Visual barriers and varied climbing structures and perches provide choice and complexity.
• Multiple resources such as feeders, water spouts and resting areas are provided to allow all animals to gain access and prevent dominant animals from monopolising them.
• Natural sunlight enters through large floor-to-ceiling windows, promoting health and well-being. The animals spend large portions of their day resting in the sunshine.
• One-way tinted glass can be used to allow the animals to observe outside activity with little stress.
• Wood and mesh double door system allows staff to enter the room for husbandry and human-animal interactions.
• Multiple hatches/pop-holes between the room and adjacent caging area prevent dominant animals from monopolising the entrance/exit. Monkeys can be trained to move through these staff-operated hatches on command, and without stress, in order to facilitate husbandry procedures such as cleaning.
• Substrate on the floor, into which seeds, grains, mealworms and other food items may be thrown provides extended foraging opportunities.
• Socially housed animals provide research opportunities for scientific programmes incorporating social aspects.

In the images above you can see:

• Macaques with access to a large room above their conventional caging below, via a pop hole.
• Staff-controlled hatches into an adjacent caging area which can be open and closed as required for husbandry purposes.
• Internal windows allowing the monkeys to view passing staff and macaques in the rooms opposite, providing additional visual stimulation.
• Rhesus macaques using the hatch doors between a large room and adjoining caged area.
• Plastic objects joined together to create a climbing frame, positioned in the bay window.

Considerations

• Where rooms are used as housing, they should be spacious to allow a full range of natural behaviours.
• The room needs to be made safe for both staff and animals with respect to electrical outlets, lights, drain holes and pipes.
• The ceiling and walls must be strong enough to support sturdy hooks and environmental enrichment fixings. Macaques will run, leap and jump on fittings and these stressors need to be taken into consideration at the design stage.
• Windows are needed for good observation of the animals. There should be adequate barriers for preventing escape.
• Ideally there should be access to an outdoor area or natural light.
• Avoid drainage systems which could become easily clogged.
• Husbandry practices need to be adapted to fit this style of animal management. There are specific staff training needs, as staff members must feel confident and relaxed working closely with macaques in a free environment. The best option is to use animals of defined health status (e.g. free of Herpes B virus).

Annotated tour

Take our annotated tour of a modern, high quality caging system which helps to support good animal welfare.

Aspects of best practice

• Flexible enclosure design with moveable panels allows the space to be divided to temporarily separate individuals or groups of animals. or to combine adjacent enclosures to allow additional space or house larger groups. Plastic panels are easily cleaned and lighter than Trespa® or wood.
• The room is utilised from floor to ceiling, making good use of the available space; high perches/platforms enable the monkeys to flee upwards when alarmed.
• Broad-spectrum lighting, rather than fluorescent strip lighting, which has a more positive effect on the health and behaviour of captive monkeys in indoor housing. Dimming at lights-on and -off stimulates dawn and dusk.
• Visual barriers provide privacy and refuge. Multiple escape routes permit hierarchical species such as macaques to manage their social interactions.
• Social housing in medium-sized, stable social groups with visual and auditory access to neighbouring groups allows a range of natural behaviours.
• Bay fronts to the enclosure, verandas and windows enable the monkeys to observe, and become accustomed to, human activity. These have the added advantage of enabling care staff to observe uninterrupted behaviour patterns.
• Varied climbing structures and other enrichment devices provide choice and complexity.
• Wind-up squeeze back mechanism (upper and lower enclosure) gives greater control for human and animal safety.
• Use of hardwood, which is warmer than metal, non-slip and can be chewed, providing some stimulation and control.
• Solid floor with substrate, into which seeds, grains, mealworms and other food items may be thrown provides extended foraging opportunities.
• Multiple resources such as shelves/resting areas, feeders and water spouts are provided in each enclosure to allow all animals to gain access and prevent dominant animals from monopolising them.
• Ample space for environmental enrichment items, such as swings and ropes, for exercise and natural behaviours.
• The horizontal bars on the enclosure fronts give better visibility down the room than do vertical bars, facilitate human-animal interaction and can be used for climbing.
• Socially housed animals provide research opportunities for scientific programmes incorporating social aspects.

Considerations

• Where caging is used as housing, the cage should be spacious to allow a full range of natural behaviours.
• When utilising the full height of the room, make sure the animals cannot access the lights in the ceiling. A gridded enclosure roof will maximises light and also allow suspension of enrichment items.
• Dirty substrate and organic waste matter need to be removed from the cage; wet cleaning is facilitated by a sloped floor running to a central drain, with removable basket to avoid blockages.

Small, restrictive cages limit both the types of locomotion the animals are able to perform and the amount of physical exercise possible, which can lead to atrophy of muscles and decreased joint mobility [14,15]. The prevalence of stereotypes and other abnormal behaviours may also be higher in small enclosures than in larger, more complex ones.

Quality of space is also important, since even large enclosures can be of limited value to the animals if they are unable to make use of the space available. If spacious, modern housing systems cannot be provided (see Indoor caging), then ways of increasing the space and complexity in conventional caging should always be explored as an interim measure [5]. Consulting other facilities that have already adapted their caging will help with troubleshooting to avoid problems and maximise success.

In the image above you can see conventional stainless steel caging in a BSL3 facility which has been improved by the addition of high perches, dividers to adjoin adjacent cage units, and a solid floor with substrate for foraging. Note the cages use the full height of the room (Image credit: Karolina Westlund).

Providing an exercise and play area

Additional space and complexity can be provided to macaques housed in banks of conventional, steel caging by adjoining a purpose-built play area constructed cheaply using sturdy wood and thick mesh. This is a practical, cost-effective way of giving the animals greater opportunities for exercise and expression of natural behaviours.

Macaques can be provided with continuous or rotational access to the play area. Animals should be monitored to ensure that they use the space provided and do not remain in one part of the enclosure; if this happens, then changes to the enclosure or the home cage may need to be made.

Wood and mesh play area

Converting individual units to ‘gang caging’

Many establishments have successfully converted standard, metal cages into linked ‘gang caging’ simply by removing the partitions between adjacent and tiered units. Tunnels can also be used to link adjacent or neighbouring cages. These are simple, cost effective means of moving away from single housing. A flexible design of gang cage allows different sized groups of animals to be maintained together in a larger communal space. This type of caging has been used successfully in regulatory toxicology studies [6,16].

In contract research organisations in Europe, the gang caging system has generally been accepted and approved by client companies. Clients appreciate the benefits to both animals and science of the improved environment and the extended range of behaviours this allows. Very little concern has been expressed that the gang caging system could compromise regulatory studies, and no studies carried out in such housing have been rejected by regulatory agencies.

Adding a solid floor

Grid or slatted floors are uncomfortable for the animals and seriously limit provision of substrate. The insertion of a solid floor (by welding this into mobile units, or sealing the floor of a room) enables deep substrate to be provided (e.g. soft wood shavings) into which food items can be scattered; this occupies the animals for extended periods and helps promote calm behaviour. If a full solid floor is not possible (e.g. in a metabolism cage), a solid resting area (e.g. platform) should be provided with a foraging tray.

Incorporating cage extensions

Verandas and bow fronts, with or without solid flooring, can be attached to conventional caging to allow macaques greater lateral visibility of the holding room and other pens. This can help habituate them to human activity [6]. Ensuring verandas are not positioned to closely together, and/or visual barriers provided, will help prevent aggression between adjacent groups. Roof extensions to caging can also provide animals with additional space and visibility of the room.

Including cage furniture

If there is sufficient space, a wide selection of fixed, suspended and hanging objects give the animals items to move on and use (including to huddle and groom), and thus help provide the stimulation they need. Platforms and perches can be accommodated in most sizes of cage.

Fitting stainless steel mesh or bars to the solid sides and/or ceiling of cages will increase the available climbing opportunities. This also increases the opportunity to suspend enrichment items.

Macaques benefit from material that they can manipulate and destroy (e.g. cardboard boxes and hemp sacks) as this allows them some control over their environment by providing an element that they can change. Novel materials may be perceived to be a problem with respect to ease of cleaning or potential effects on scientific data (e.g. potential induction of liver enzymes by wood). Nevertheless, various materials have been used successfully, even in regulatory studies.

Visual barriers between and/or within enclosures allow the occupants the choice between seeing other macaques and humans, or hiding from them. This enables them to have greater control over their social interactions, helps minimize intra and inter-group aggression and promotes successful pairing and grouping [17-19]. Examples of visual barriers are floor mounted or hanging plastic panels, sacking or large wide pipes or barrels. They should be carefully positioned so that they do not block light sources.

Adapting enclosure materials

Wood is less cold and noisy than metal, provides a softer textured surface and facilitates a variety of species-typical behaviours, as it can be manipulated and chewed. Natural branches and/or wooden perches can be included to provide additional usable space. The type of wood must not be toxic to the animals; maple, beech and oak are all safe. If real wood cannot be used, then plastic is a good alternative.

Staff safety is the primary consideration in studies involving macaques infected with dangerous pathogens and is assessed by a hierarchy of options:

• Removing the hazard – is the work necessary? (e.g. could a less dangerous species, a surrogate, or a less dangerous pathogen be used?).
• Isolating the hazard by primary containment (e.g. totally enclosed cabinets, plastic film isolators, individually ventilated cages).
• Partially isolating the hazard (e.g. by a combination of strategies, such as a directional flow system, transfer boxes, downdraught tables, personal protective equipment and respiratory protective equipment).
• Isolating the individual operator from the hazard (e.g. full airsuits or ventilated two-piece suits, such as Martindales).
• Staff vaccination.

Animal welfare is also an important consideration, for scientific and ethical reasons. Public Health England (PHE) has developed a state-of-the-art containment system which balances the need for staff safety at all stages of the experimental process, whilst addressing the requirements of macaques for space, environmental enrichment and social interaction. The system has been used in a series of studies involving biocontainment level 3 infectious agents (BCL3), such as Mycobacterium tuberculosis, Bacillus anthracis, Burkholderia pseudomallei and monkeypox virus administered by aerosol challenge (the most hazardous route). It allows group housing whilst offering quantifiable operator protection during infection, husbandry, experimental sampling and necropsy. The general principles for refinement can be modified to apply to BCL4 agents.

Containment system

The containment system utilises the principle of directional airflow away from the operator towards the back of the cage system in order to protect staff. A series of interconnected cages are placed inside modular booths that have a clear rigid plastic screen at the front of the system. This screen allows good observation of the macaques within the cages whilst providing protection from physical contamination by urination, defecation, cough, throwing of objects or by reaching through from the cage.

Each screen is fitted with flap valves that control the velocity of the air into the system and each has a number of small access doors placed in strategic alignment with the cage front to allow animal care staff access to replace food and water, change bedding and sedate the occupants for subsequent procedures. The number of airborne organisms is reduced by using this directional airflow away from the operator towards the rear of the cage. With correct operation this flow is maintained at a minimum of 0.7M/second and the air removed from the rear of the cage is extracted by a total-loss room air handling system via HEPA filtration. Further operator protection is provided by using a transfer box for sedated animals and a downdraught table for more risky procedures, such as blood sampling, broncheoalveolar lavage, X-rays, close clinical assessment and necropsy. 

Animal welfare needs are provided for by incorporating group housing and pre-training into the study design (see below), utilising full height cages that meet the standards of Directive 2010/63/EU and Appendix A to Convention ETS 123, and providing foraging enrichment and toys such as balls, wooden dumbbells, chains and mirrors.

Cages used for studies involving infectious agents need to be able to withstand robust decontamination processes, such as autoclaving and fumigation, that are required at the end of a study to provide for staff safety and for the scientific integrity of the following study. Whilst stainless steel is the obvious choice as a material for such cages, other materials can be used to provide a softer and less noisy environment, such as Trespa® for cage partitions and polypropylene for platforms, shelves and perches.

Group housing

Group housing has been used without problems in terms of cross-infection, provided that all animals housed in each group receive the same treatment, such as the infectious dose and/or vaccination regime. Vaccinated and naïve animals are not housed together where a live vaccine such as BCG or a vaccine using a live viral vector is being used, as the close association of cage mates could bring about immune stimulation of the unvaccinated animals and compromise the results of the experiment. Compatible groups of up to six macaques have been housed together successfully with no confounding effect on the experimental outcomes.

In the image above, it can be seen that the two animals housed together show the same level of disease pathology and that this is dependent upon the initial dose given rather than any cross-infection. 

Pre-training and acclimatisation

When working with dangerous pathogens, physically restraining macaques to administer substances by gavage is not a safe option, and where significant volumes of blood are required it would be difficult to sample safely from an unsedated individual. What can be achieved, however, is training of the animals to take an oral dose of, for example, an antibiotic. Typically macaques at PHE are trained using positive reinforcement techniques to: i) station (move to a specific location in their home cage) so that all individuals can be effectively dosed without interference; and ii) co-operate by presenting themselves for intramuscular injection of a sedative, so that procedures such as X-ray, weighing and temperature measurement, which are vital to clinical assessment, can be conducted safely and with minimal stress caused to the animals. Staff members, including researchers, are actively encouraged to interact with macaques before the infection phase of an experiment in order to familiarise the animals with the presence and behaviour of humans. Training the animals to receive an oral dose, to remain stationed whilst others receive theirs, and to come forward for injection is now an integral part of the experimental protocol. It is considered that this will lead to scientific benefit in terms of the reproducibility of results.

Due consideration is also given to the changes to the macaques’ environment that will occur once infectious challenge has taken place. For example, the animals can be acclimatised to changes in the appearance of staff wearing protective clothing, for short periods before challenge. Similarly, the animals can be introduced to containment housing prior to challenge so that they acclimatise to this novel environment. Some establishments do this by placing open cages within a larger gang pen set up, so that animals grow used to the cages, can enter and leave them at will and can use them as a refuge or feeding station.

Environmental enrichment

When using some pathogens, it is not good containment practice to allow animals to have direct contact with floor substrate. However, a grid floor can be provided above a tray containing substrate such as Enviro-dri® or SizzleNest® to allow foraging behaviour. Alternatively, or additionally, puzzle feeders and forage boxes can be placed within the cage where they do not obstruct any dividing or restraining mechanisms. Forage boxes can be made of cheap, simple disposable materials, such as cardboard. PHE has also demonstrated that the environment within biocontainment can be effectively enriched via the use of ropes/rope ladders or by hanging high value food items within suitable containers hung from chains. Such items increase the complexity of the cage environment and the opportunities for interactive behaviour.

Whilst items such as rope and plastic feeders or balls placed within the cage environment have the potential to become contaminated with the infectious agent, this has not caused issues with the outcome of studies at PHE. Some items may be robust enough to withstand decontamination by autoclaving, but it is considered better practice to dispose of such items at the end of each study after making them safe by the most suitable method.

Control

When using highly infectious agents, the risks associated with the husbandry and experimental handling of non-human primates must be controlled by strict discipline with regard to feeding, watering and waste removal regimes. For these activities staff members are trained to adhere to a protocol described in a code of practice.

he setting of robust, early experimental end points, using a range of clinical and behavioural parameters or microbiological indicators, minimises animal suffering and reduces risk to staff. For example, a read-out end point for protection or efficacy could be virus isolation or viral load by polymerase chain reaction (PCR) in untreated controls before onset of disease (pilot experiments may be required to verify that this, combined with other clinical parameters, correlates with progression to disease). This is obviously better from both an animal welfare and staff safety point of view rather than allowing progression to severe disease. This is an area where there is a strong case for data sharing on national and international levels, so that research groups can learn from previous work and not repeat experiments to establish such end-points. Clinical monitoring can be carried out by taking X-rays, or more advanced imaging such as computed tomography [20] or Magnetic Resonance scanning [21], and by using telemetry implants to monitor heart rate, blood pressure, temperature, activity and respiration rate. Previously, telemetry systems available required the macaques to be separated during data capture to avoid cross talk interference that may render the data meaningless, although they could be housed with non-implanted companions. However, telemetry systems have now been developed that allow simultaneous data capture from telemetered group-housed animals. In order to monitor animals for the onset of clinical signs there needs to be a commitment to round-the-clock monitoring for infected animals. This may mean that staff members need to enter the animal room on a regular basis throughout the night or, alternatively, observation can be made using closed circuit television (CCTV). It has been found that this is not only more convenient for staff but also is less disruptive for the animals. Furthermore, clinical assessment of animals that have been disturbed by the entry of an observer can be far less informative than remote observation of animals unaware of, and not stimulated by, the presence of humans.