Chapter 1: Construct laboratory animal cages

Laboratory animal husbandry is a crucial field in applied biology that ensures the well-being and ethical management of animals used in research and teaching. Proper construction and maintenance of animal cages directly impact the health, behavior, and experimental validity of laboratory animals. In Kenya, where research institutions and universities increasingly rely on animal models, understanding the design and upkeep of animal housing facilities is essential for professionals engaged in applied biology. This chapter explores the fundamental aspects of laboratory animal cages, focusing on the types of laboratory animals, animal house design, and effective disinfection and cleaning protocols.

1.1 Introduction to Animal Husbandry

Laboratory animal husbandry is the care, housing, feeding and breeding of animals kept for research, teaching and testing. The animals live entirely in the environment that the technician provides, so the quality of that environment decides both their welfare and the reliability of the results obtained from them. A cage that is too small, a room that is too hot or an animal house that is hard to clean will stress the animals and introduce variation that no statistical method can remove.

Good practice rests on the 3Rs, which guide every decision in a laboratory animal facility. Replacement means using a non-animal method when one can answer the question. Reduction means using the smallest number of animals that gives valid results. Refinement means changing housing and procedures so that pain, distress and fear are kept to a minimum. This topic introduces the animals, the animal house that holds them, the cages, and the cleaning that keeps both safe.

1.1.1 Laboratory Animals

Laboratory animals are species that are bred and kept under controlled conditions for scientific work. They are chosen for their small size, short generation time, ease of handling and well-known biology. Their needs for space, temperature, diet and company differ from species to species, and a technician must know these needs before building or buying a cage.

Species kept in teaching and research laboratories

• Mice: small, quick to breed and available in many inbred and outbred strains. They are widely used in pharmacology, toxicology, immunology and genetics.
• Rats: larger than mice, which makes blood sampling and surgery easier. They are used in nutrition, toxicology, behaviour and physiology studies.
• Rabbits: used for antibody (antiserum) production, pyrogen testing and some toxicology work. They need large cages with room to stretch and hop.
• Guinea pigs: used in nutrition research, such as vitamin C studies, and in some infectious disease work. They cannot make their own vitamin C and need it in the diet, and their cages need solid floors.
• Hamsters: used in some parasitology and virology studies and in cheek-pouch tissue work.
• Zebrafish: used in developmental biology and genetics. They are kept in tanks with water filtration and water quality control, not in cages.

Criteria for selecting laboratory animals

• Purpose of the study: the species must show the biological process being studied. A study of antibody production needs an animal that gives a good immune response and enough blood.
• Ethical justification: the study must have been approved by an animal ethics committee, and the species should be the one that causes the least distress while still answering the question.
• Genetic uniformity: inbred strains give more uniform responses than outbred stock, so fewer animals are needed. Outbred stock is chosen when genetic diversity is part of the question.
• Health status: animals must come from a source with known disease status, so that infections do not alter results or spread through the colony.
• Space and resources: the cost of housing, feed and care grows with animal size, so the smallest suitable species is usually preferred.
• Age and sex: young adult animals of a defined weight and sex reduce variation between groups.

Animal welfare considerations

• Environmental enrichment: nesting material, shelters and gnawing blocks let animals express natural behaviour such as burrowing, hiding and chewing, and reduce stress.
• Social housing: mice, rats, rabbits and guinea pigs are social, and they are normally housed in compatible groups unless the study or aggression requires single housing.
• Daily observation: each animal is checked every day for changes in appetite, posture, coat, breathing and behaviour, and any sick animal is reported at once.
• Humane endpoints: the point at which an animal must be removed from a study to prevent suffering is defined in the approved protocol before work begins.
• Trained handling: only trained staff handle animals, using calm and confident methods, because rough handling frightens the animals and also injures staff.

1.1.2 Animal House Design

An animal house is a building or a suite of rooms designed to keep animals healthy, keep the results of experiments reliable and protect the people who work in it. The design controls the environment, limits the movement of people, animals and waste, and allows all surfaces to be cleaned thoroughly. A well designed animal house in a teaching laboratory or a research station has separate rooms for separate functions, and a one-way flow from clean areas to dirty areas.

Environmental control in the animal house

Temperature, humidity, ventilation and lighting are controlled because the animals cannot adjust to wide changes. The temperature and humidity values are the ranges given in the widely used Guide for the Care and Use of Laboratory Animals, and the air change figure is its guideline; the Guide asks for a controlled light cycle, and 12 hours light and 12 hours dark is widely used. A facility may set tighter limits for its own species and studies.

Noise is also kept low and steady, because sudden loud sounds stress animals and can upset breeding.

Layout and zoning

The rooms are arranged so that clean and dirty work do not cross. A typical suite has a quarantine room for new arrivals, breeding rooms, experimental rooms, a procedure room, a cage-washing area, a store for feed and bedding, and a waste holding area. Staff and materials move from clean rooms to dirty rooms, never back. Species are kept in separate rooms so that diseases and odours do not pass between them, and healthy breeding colonies are kept away from animals that have been used in experiments.

Safety and biosecurity measures

• Restricted access: only authorised, trained staff enter, using a changing area where they put on a clean laboratory coat or gown, gloves, a mask where needed and dedicated footwear.
• Airlocks and pest control: a double-door entrance and wire mesh over vents keep out wild rodents, insects and birds, which can introduce infection.
• Waste handling: soiled bedding, carcasses and sharps leave the facility by a defined route and are never carried back through clean areas.
• Emergency provisions: fire exits, a backup power supply for ventilation and fridges, and an eyewash station are provided because animals cannot be evacuated quickly.

1.1.2.1 Partitions

Partitions are the walls and dividers that separate the rooms and areas of the animal house. They keep species apart, divide the clean zone from the dirty zone and hold in noise, odours and airborne dust. Partitions must be strong enough to resist impact from trolleys, and they must have surfaces that can be washed and disinfected without damage.

• Solid walls between rooms: sealed blockwork or panels reach from the floor to the ceiling so that dust and animals cannot pass over the top.
• Smooth, joint-free finish: walls are plastered and finished with washable epoxy paint, glazed tiles or glass-reinforced plastic sheets, so that no crevices hold dirt or pests.
• Coved junctions: the wall meets the floor in a smooth curve, not a sharp corner, so that the angle can be swept and mopped completely.
• Doors: doors are solid, self-closing, tight fitting and fitted with a vision panel so that staff can check a room without entering.
• Corridors and glass screens: a clean corridor and a dirty corridor, or a transparent screen at the observation point, let staff watch animals without disturbing them.

1.1.2.2 Construction Materials

Materials for floors, walls, ceilings and fittings must be durable, non-toxic, waterproof and able to withstand frequent washing with detergents and disinfectants. Materials that absorb water, crack or rust encourage microbial growth and make cleaning ineffective.

Windows are usually avoided in rodent rooms, because daylight and heat change the controlled light cycle and temperature.

1.1.2.3 Animal Cages

A cage is the animal's immediate living space. It must give enough room for normal movement and rest, allow the animal to be seen, keep it from escaping and be easy to clean. The material, design and size of the cage depend on the species.

• Polycarbonate or polypropylene boxes: these clear plastic boxes with a stainless steel wire lid are the standard for mice and rats. They can be autoclaved and let staff see the animals.
• Stainless steel cages: these are strong, can be sterilised many times and are widely used for rabbits and guinea pigs, which gnaw and are heavier.
• Individually ventilated cages: each cage is supplied with filtered air, which lowers the spread of infection between cages and the build-up of ammonia.
• Bedding: dust-free wood shavings, paper-based bedding or similar absorbent material cover the floor, absorb urine and give the animals material for nesting.
• Feeders and water: a wire food hopper and a sipper bottle or water tube are fitted so that animals can eat and drink without contaminating the food or the water.
• Cage labels: each cage carries a card that lists species, strain, number and sex of animals, project number, dates and the responsible person.

The following floor areas for group housing follow the Guide for the Care and Use of Laboratory Animals and give a reference point for sizing a cage.

Cage height is at least 12.7 cm for mice and 17.8 cm for rats.

Steps for constructing a simple stainless steel rabbit cage:

1. Decide the size from the species, the weight of the adult animal and the number of animals per cage, so that the animal can stretch, turn round and stand on its hind legs.
2. Select stainless steel sheet for the sides and tray and stainless steel wire mesh for the floor and door. Choose a mesh size that supports the feet without trapping them.
3. Mark and cut the panels accurately, then file or grind every edge until it is smooth, because a sharp edge injures animals and staff.
4. Join the panels by welding or riveting. Fit the mesh floor with a removable droppings tray below it.
5. Fit a door with a secure latch that the animal cannot open, and mount a feeder and a bracket for the water bottle on the outside so that they can be filled without opening the cage.
6. Wash the finished cage with detergent, rinse it and inspect it for burrs, gaps and loose wires before any animal is introduced.

1.1.3 Disinfection and Cleaning of Animal House

Cleaning removes dirt, droppings, hair and organic matter. Disinfection then reduces the number of microorganisms that remain. Disinfection works only on a clean surface, because organic matter shields microbes and neutralises many disinfectants. A regular and recorded routine prevents the build-up of ammonia and the spread of infection, and keeps experimental results reliable.

Cleaning frequency and scheduling

A written schedule lists what is cleaned, how often and by whom. The following frequencies are common, and they are shortened when cages are wet, soiled or overcrowded.

• Daily: remove dead animals and wet bedding, refill feed and water, and wash and disinfect the floors of the animal rooms.
• At least weekly: change the bedding and wash cages, water bottles and feeders. Cages in ventilated racks may be changed less often because filtered air keeps them drier.
• Between studies or after a room is emptied: wash and disinfect the room completely, including walls, shelves and racks, before the next group enters.
• Periodically: wash and disinfect ceilings, ventilation grilles and drains, and service the cage washer and autoclave.

Cleaning agents and disinfectants

Never mix bleach with acids or with ammonia-based cleaners, because the mixture releases toxic gases. Animals are removed from a room before it is disinfected, and surfaces are rinsed and dried before they return.

Cleaning procedures

1. Put on gloves, a laboratory coat or gown, safety boots and eye protection, and a mask in dusty areas.
2. Move the animals into clean cages, or into a clean holding area, using gentle handling.
3. Empty the dirty cage into a waste container. Soiled bedding is treated as biological waste and removed by the agreed waste route.
4. Scrub the cage, lid, feeder and water bottle with detergent and warm water to remove all visible dirt.
5. Apply the disinfectant at the recommended dilution and leave it on the surface for the full contact time given by the manufacturer.
6. Rinse thoroughly with clean water to remove residues, because animals lick surfaces and chemical residues can harm them.
7. Dry the cages completely, or autoclave them where required, and refill them with fresh bedding, feed and water before the animals return.
8. Wash floors and walls from the cleanest area to the dirtiest, and clean the cleaning tools afterwards.

Monitoring and documentation

Visual checks are recorded after every cleaning, and swabs or contact plates from cages, racks and floors are tested at intervals to confirm that the routine works. Health monitoring of sentinel animals, which are kept in the room to show what infections are present, gives further evidence. Cleaning logs record the date, the area, the product and dilution used and the person who cleaned. Written standard operating procedures and training records show that the work has been done correctly.

Chapter Summary

This chapter provides a comprehensive overview of laboratory animal husbandry focusing on the construction of animal cages. It begins by defining laboratory animals and their role in scientific research, emphasizing the need for proper care and management. The design of an animal house is explored in detail, covering essential aspects such as partitions that separate different species or groups to prevent cross-contamination and stress. Various construction materials suitable for durability, hygiene, and animal welfare are discussed, highlighting their importance in maintaining a safe and functional environment. The chapter then concentrates on the specifications and features of animal cages that support the health and comfort of laboratory animals. Finally, it addresses the critical procedures for disinfection and cleaning of the animal house to ensure a sterile environment that minimizes the risk of infection and promotes ethical research practices.