Part 3.3 Climate Control
This is Part 3.3 of the Code of Practice for the Housing and Care of Laboratory Mice, Rats, Guinea Pigs and Rabbits.
The climate experienced by the laboratory animal is that of the 'microenvironment' in its enclosure. Except where animals are housed in ventilated rack systems or IVCs, climatic variables are generally set and controlled for the room or 'macroenvironment' in which the animal enclosures are located.
Controlling the microenvironment through the macroenvironment requires an understanding of how the components of climate are affected by the type of animal enclosure.
The design of the animal enclosure, the materials used in its construction, the type of bedding and the stocking density all affect the climate of the microenvironment and consequently the welfare of the animals. In addition, variations in any one of these parameters may impact on the experimental results as well as the working conditions for personnel.
Monitoring and recording the conditions inside the macro- and microenvironments is essential to good climate control. Emergency plans should be in place, including mechanisms to alert appropriate personnel in the event of power failure or unacceptable changes in climatic variables.
Laboratory mice and rats generally choose to manipulate their own microenvironments via activities such as huddling, nest building, tunnelling and burrowing. In general, the rodent's ability to control temperature, humidity and lighting is as important to its welfare as specifying ambient conditions within the room.
Temperature and humidity should be considered together due to their close interrelationship. Animals show a graded thermal and adrenal stress response to increasing effective temperature (an index of animal comfort),regardless of actual temperature.
Neonates have no autonomous thermoregulation in the first week, but their appropriate thermoneutral zone is 30 to 34°C. This is normally achieved within the microenvironment of a well structured nest. Lactating females have a higher metabolic rate and show a preference for lower temperatures. Old, sick, nude, immunocompromised or experimentally stressed animals generally have poor homeostasis. Variability in ambient temperatures is more likely to result in changes in their body temperature, resulting in further stress.
Uniformity of temperature throughout a room will depend on the effectiveness of ventilation and the positioning and material of cages or boxes in a racking system. There is an effect due to heat conduction within a rack of rodent cages from the body heat of the animals — the cages at the top and middle may be up to 5°C hotter than the bottom cages.
In general, this species is better able to withstand cold than heat, if provided with sufficient bedding and protection from draughts. Reproductive rates will decline significantly if room temperatures are above 25ºC for any length of time. Pregnant sows are susceptible to heat stress at higher temperatures (such as > 30ºC) and survival of young is greatly reduced at 17ºC.
Low temperatures are fairly well tolerated by rabbits but heat and drafts are not well tolerated. Temperatures above 30°C, combined with high relative humidity, can cause heat stress, which may result in infertility or mortality.
Minimum standards for room temperature:
- Room temperatures must be measured and recorded once daily and maximum and minimum values must be recorded wherever possible.
- Room temperature must be maintained within the temperature range specified for each species (see Appendix 1).
- When housing very aged, very young or hairless animals, or animals with a reduced thermoregulatory capacity as the result of genotype or an experimental protocol, higher room temperatures than those indicated in Appendix 1 may be required. Suitable bedding material or thermal heat pads must be provided for such animals.
- Laboratory animals are very susceptible to sudden fluctuations in temperature and these should be avoided wherever possible.
- In setting the temperature of the animal room, consideration must be given to the potential impact of sunlight, the heat generated by animals, and the rate at which heat is dissipated from cages. For example, open, metal or wire cages lose heat more quickly than plastic ones, and more animals generate more heat.
- The design and furnishing of the animal enclosure should be conducive to assisting the animals to thermoregulate. The animal enclosure should enable group-housed animals to warm themselves by huddling together or by using bedding or nesting material and also provide sufficient space for animals to disperse to increase heat loss.
- Temperature should be continually monitored, and an optimum range thermostat set. It is desirable that monitored room temperatures are centrally displayed in the animal house. In addition, the temperature in a representative range (such as top, bottom and middle locations in a rack) of the smallest unit of animal housing should be monitored periodically. Note: the temperature in the individual cage may be up to 5°C higher than the room temperature, depending on the stocking density and position of the enclosure in the room.
Species specific recommendations
- It is recommended that room temperature be maintained within 15 to 24°C.
3.3.2 Relative humidity
Owing to the inter-relationship between humidity and temperature, at a given temperature higher relative humidity causes an increase in effective temperature. Room ventilation and stocking rate of the enclosure impact on relative humidity as the respiration of animals and evaporation from excreta generate moisture inside the enclosure.
Humidity variations are less significant than temperature variations. Low relative humidity causes higher dust levels, increased levels of respiratory infections and possible skin lesions. High relative humidity increases thermal stress and ammonia levels, and lowers resistance to infection.
Minimum standards for relative humidity:
- Relative humidity in enclosures must be kept within the range of 40 to 70% wherever possible.
- Enclosed tops, such as filter tops or cage bonnets, can significantly impede airflow, trap moisture inside the cage and raise humidity. Allowances should be made accordingly.
- Room humidity should be monitored and kept well below 70% to ensure that the relative humidity of the enclosure stays within the acceptable range. Refer to figures in italics and brackets in Appendix 1 for the species specific recommended levels of relative humidity in the animal enclosure.
3.3.3 Ventilation and air quality
Ventilation regulates temperature and humidity, controls air quality and facilitates the movement of air between the macro- and micro- environments of the room. Like temperature and humidity, ventilation is usually controlled at the room level, but it is the conditions at the level of the animal enclosure that are important. These, in turn, are affected by the size and thermal load of the room and the stocking density and design of the animal enclosures. Wire grid-floored cages or boxes have approximately 90% of the room ventilation rate, while solid floored enclosures have approximately 60% of the room ventilation rate. Filter-tops on enclosures markedly restrict air exchange and can increase ammonia levels by 50 to 100%.
The most common gaseous contaminant in animal facilities is ammonia resulting from the decomposition of nitrogenous waste in excreta. Poor ventilation, increases in relative humidity and poor hygiene all contribute to elevated concentrations of ammonia which can irritate the respiratory tract and increase the susceptibility of animals to respiratory disease.
Ammonia may exceed 25ppm in rodent cages when bedding changes and cleaning are due. At this time, the room ammonia level may be less than 10ppm. Ammonia above 25ppm inside rodent cages is a potent co-irritant and can act synergistically with respiratory pathogens. Rabbits are even more sensitive to ammonia build-up.
Sealed IVCs are potentially dangerous, as animals may die rapidly if the ventilation fails and there is nobody to intervene. In sealed IVCs where ventilation fails, carbon dioxide can rise above 30 000 ppm (3%) in under 30 minutes, and above 50 000 ppm (5%) in little over an hour. Unrectified ventilation failure over a couple of hours is likely to be fatal.
Minimum standards for ventilation and air quality:
- Fully operational rooms or IVCs for laboratory animals must be provided with draught-free, fresh or conditioned air distributed continually and throughout.
- Average concentrations of ammonia in animal rooms must not exceed 25ppm over an 8 hour day, which is also the upper limit for human occupational health.
- Average concentrations of ammonia in the smallest unit of animal housing must not exceed 25ppm.
- Recirculating ventilation systems must be regularly serviced.
- Consideration should be given to the two components of ventilation — air speed and air movement, which cover the number of air changes per hour and air quality.
- Ventilation should be sufficient to prevent the build-up of noxious carbon dioxide, ammonia, humidity, dust and infectious agents. While 10 to 20 room ACH may be adequate for conventional animal rooms, this rate does not guarantee that ventilation will be adequate at the enclosure level, particularly if filter tops are used.
- Concentrations of carbon dioxide in IVCs should be less than 5000ppm (0.5%). Refer to Section 4 for available air quality monitoring devices.
- Bedding or nesting material should be considered in conjunction with ventilation as its absorptive properties can decrease the production of ammonia. Refer to (vii) and (viii) regarding the measurement of ammonia levels.
- The air distribution system should be configured to maximise energy efficiency and deliver as even a proportion of air as possible to each animal enclosure. Careful attention should be given to inlet and outlet positions to ensure good air circulation and avoid draughts and noise.
- Ventilation systems should be set at differential air pressures within a building to meet the different requirements of 'barrier systems', such as those used in PC3, PC4 and SPF conditions. For example, higher pressures should be used in clean areas relative to dirty or biohazardous ones, in order to minimise contamination. In addition, germ-free or defined flora populations, SPF breeding facilities, and colonies of aged, immunocompromised animals or those involved in disease models require a higher level of control of the microbial environment than that used in conventional housing. (See Sections 3.2.5 and 3.7)
- To prevent excessive levels of ammonia in animal enclosures, consideration should be given to reducing stocking densities, open versus closed shelving, frequent cleaning and avoiding the use of filter top cages.
- Humans can smell ammonia at a concentration as low as 8ppm and any smell of ammonia should be investigated. The concentration of ammonia should be monitored using one of the available gaseous detection devices placed in the animal enclosure see (viii).
- Care should be taken when selecting and using an ammonia gas detection device and interpreting the measurement. Some devices directly measure an instantaneous concentration of ammonia, whilst others provide a time weighted average concentration measurement (accumulated measurement of ammonia ppm/time hrs = average concentration of ammonia). There is ongoing discussion as to which measurement provides the most accurate reflection of irritant levels of ammonia. Refer to Section 4 for available air quality monitoring devices.
Species specific recommendations
- As rabbits shed considerable amounts of hair, the extract ducts should be cleaned regularly to ensure continued efficiency of ventilation.
- As rabbits are particularly sensitive to ammonia build-up, instantaneous ammonia concentrations inside rabbit enclosures (at the level of the rabbit nose) should be 10ppm or less.
3.3.4 Noise and vibration
The control of noise and vibration is important in the care of laboratory animals. Loud, intermittent and unfamiliar sounds are probably more disruptive than constant sounds. Prolonged noise over
100dB, or 160dB short-term, cause inner ear damage, noise-induced seizures and other problems to rodents.
Different laboratory animal species hear different pitch and loudness. Laboratory animals are sensitive to ultrasound, which can cause behavioural disturbances, and they are also able to hear frequencies that are inaudible to humans. Rodents communicate at 10 to 70kHz, compared with the human audible range of up to 20kHz. In addition, it is known that rats are particularly sensitive to ultrasound and that rodent neonates use ultrasound to communicate.
- Intense noise should be avoided as it can cause alterations to inner ear, gastrointestinal, immunological, reproductive, nervous and cardiovascular systems, as well as metabolic and behavioural aberrations.
- Background noise (including ultrasound) should be kept below about 50dB (eg radio) and should be free of distinct tonal content.
- Short exposure noise should be kept to less than 85dB.
- Excessive noise and vibration most commonly arise from imperfectly balanced rotating or reciprocating machinery, particularly on start up. Machines that switch on and off intermittently may require special precautions as they may transmit vibrations over considerable distances. Vibrational stability is of greater concern for animal facilities located on the upper levels of a building. The density of ventilated racks will affect the noise level.
- Noise and vibration should be controlled in an animal facility through design and construction of the facility, and through the appropriate selection of equipment, and shielding and dampening devices.
Species specific recommendations:
Guinea pigs and rabbits:
- As guinea pigs and rabbits are easily startled by sudden noise, and may injure themselves in panic, care should be taken to minimise the generation of extraneous noise in the vicinity of these animal, therefore some form of low-level background noise in the animal room may be suggested.
Mice, rats, rabbits and guinea pigs are either crepuscular or nocturnal. Their eyes are therefore adapted to dim light conditions. Light-induced retinal damage occurs principally in albino animals, even under normal lighting conditions (over 60lux), and may lead to blindness with exposure to light above 100lux for longer than 16 hours daily. Light intensity can influence aggressiveness and the incidence of cannibalism in rodents.
There is uncertainty as to whether laboratory rabbits are diurnal, nocturnal or crepuscular. It appears that external noise and scheduled feeding during the day can turn laboratory rabbits (and other animals) into predominantly diurnal animals.
The important aspects of light to consider are intensity, wavelength and photoperiod.
Minimum standards for lighting:
- The maximum allowable light intensity in an animal room is equivalent to 350lux at one metre height.
- Animals must have the opportunity to withdraw to lower light intensities, especially those in top racks and albino animals.
- Periods of light and dark must be provided to the animals each day.
- Light intensity in the animal room for safe and effective performance of routine animal care and laboratory activities should be considered.
- Light intensity may vary considerably between top and bottom cages in a rack. Shelters or bedding should be provided within animal enclosures to enable animals to regulate their exposure to light. Light covers should be used where needed to diffuse and soften room lights.
- Lighting should be provided by natural light or fluorescent light that duplicates the characteristics of sunlight.
- Varied light or dark cycles are required to regulate breeding and circadian rhythms. Consideration should be given to providing a warning light outside animal rooms to indicate dark cycles because light interruptions during the dark phase may significantly skew endogenous rhythms. Animals may take 10 to 14 days to adapt to any change in photoperiod.
- A red light source can be used for human activities during dark cycles. Alternatively, a separate room should be used for care-related activities.
- Whenever possible, lighting should be monitored at the room level and centrally controlled.
3.3.6 Emergency plans and alarms systems
Minimum standards for emergency plans and alarms system:
- Animal facilities must be able to detect fire or the breakdown of essential climate control equipment such as ventilation and temperature control systems.
- Animal facilities must have in place emergency plans.
- The heating, cooling and ventilation should be monitored to ensure that acceptable environmental conditions are maintained at all times. This is particularly important for individually ventilated cage systems, as fatal levels of carbon dioxide may accumulate within a couple of hours of ventilation system failure.
- The operation of the alarm system should cause minimal disturbance to the animals where possible. For example, a tone generator can be used to reduce the frequency and decibel level of an existing alarm, or there is the 'silent' alarm, which is inaudible to small rodents. Most rodents cannot hear frequencies up to 1000kHz, whilst guinea pigs can hear frequencies from 200 to 2000kHz. Refer to Section 4 for available 'silent' alarm products.