Management of Microenvironment in Laboratory Animal (rats, mice) House

June 8, 2021

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Management of Microenvironment in Laboratory Animal (rats, mice) House

Introduction

The development and specialization of laboratory animal sciences started in 1950s. Laboratory animal are primarily used for research, drug testing, and teaching purposes, although the current norms prevent their application for teaching purposes in most of the countries. The rat and mice collectively contribute to a significant 77 % of the total laboratory animals used by humans. An optimum environment in the animal house is essential for maintaining ideal conditions, necessary for quality research, teaching, testing or breeding processes. The animal house must provide adequate space for growth, activity, behaviour, reproduction and well being of the animals. Animals display their natural behavior, traits and are healthy only if the housing conditions are comfortable. Crowded animal houses with bad micro and macro environmental conditions and poor management results in suppression of natural physiology and behavior. The result will be stunted growth, altered metabolism due to stress and the research results will be dubious and breeding program or testing will suffer. A through understanding of different environmental variables and how they influence animal well being is essential for successful maintenance of laboratory animals.

The environment

As laboratory animals are extensively reared, maintenance of optimum environmental conditions becomes mandatory. Livestock or domestic animals which are reared in free stalls, open spaces, sheds or barns display various physiological, behavioral strategies to adapt to changing environmental conditions. But if environmental conditions and housing are not optimum, laboratory animal cannot acclimatize and gradually are stressed. The different types of environments to consider are,

Macroenvironment: It is the environment outside the animal house [Secondary enclosure].

Microenvironment: It is the environment or the physical conditions inside the animal house or animal cages or enclosures [Primary enclosure].

As the laboratory animals are reared in closed houses or cages, suboptimal microenvironmental conditions can adversely affect the normal animal physiology, behavior, alter metabolism and predispose them to different diseases. Temperature, humidity, light, ventilation, air quality and noise are the variables to be continuously monitored and regulated in animal house.

Temperature

Animals are most comfortable within narrow temperature ranges. This optimum temperature range is called as thermoneutral zone [TNZ], where negligible energy is lost or gained to maintain a constant body temperature. Temperatures above / upper critical temperature [UCTs] and below / lower critical temperatures [UCTs] the thermoneutral range require expenditure of energy, either to cool down or warm up. If ventilation and air flow is not optimum, there can be collective build up of heat inside the animal houses or cages very quickly subjecting the animals to heat stress. Conversely, if the temperatures are kept far below LCT, it leads to cold stress. Here care should be taken to provide nesting material to the animals so that they can sustain cold comfortably. Adjustment of temperatures within the TNZ or slightly below the LCT is a routine practice in animal houses. Temperatures are usually set in between UCTs and LCTs ranges in animal houses, and wide fluctuations in microclimatic conditions should be avoided. For example, the TNZ for mice ranges between 20 to 26^°C (higher ranges 26^°C and 34^°C) and they are comfortable at a temperature slightly above 26 to 29°C. However reproductive group’s performances are optimum at 22 to 28^°C.

Humidity

Similar to temperature optimum relative humidity is also associated with thermoregulation. Very low levels of humidity cause irritation and water loss from skin and too high humidity compromise the heat dissipation ability to the surroundings. Abnormal humidity and temperature affect the thermoregulation mechanisms, increase the stress and force the animals to make adaptive metabolic behaviours. Optimum combination of ambient temperatures and relative humidity index [THI] are essential for animal comfort. Normal relative humidity range in animal houses should be between 40-70 % for mammalian species. Excess humidity in animal cages can be confirmed by presence of ammonia, which irritates the respiratory membranes. Other common manifestations of low or high humidity include mortality, preweaning mortality, tail necrosis, increased diseases and other skin ailments. Humidity should also be set to comfortable 70 % outside the primary animal house.

Note:

Newborn animals require marginally higher humidity levels till weaning (closer to 70% humidity levels).

Ventilation

Ventilation provides air quantity and quality essential to maintain microenvironment in the animal houses. As the microenvironment has to be tightly regulated, air movement plays a very important function to provide essential oxygen to animals, dilutes gaseous metabolic wastes, odours, carries away excess heat and removal of air born microbe and pathogens. The flow of air should be maintained to 10-15 air changes/hour (maximum 120 air changes/hour) and be smooth, as drafts (air with high velocity) have a higher cooling effect which might lead to problems in sick, operated, treated or infant animals. Air speed below 0.2 m/sec is optimum to suffice the ventilation needs for lab animals. Wire grid-floored cages/boxes are the best and have approximately 90% and solid floored enclosures have approximately 60% of the room ventilation rate, respectively. While, filter-tops on enclosures markedly restrict air exchange and also increase ammonia levels (50-100%). Ammonia levels over 25 ppm are dangerous and seriously irritative, thus increasing respiratory disorders. Air inflow and periodic replacement inside the animal house or cages should be decided on number of animals caged, age, gender, species variation, total air pressure, type of esperiment and properties of bedding material.

The advance systems of heating, ventilation and air conditioning [HVAC] can be set according to ventilation needs of animals. There are three important things to remember, always provide slightly more air exchange than the absolute amount required, regular validation of the system to check accuracy and reventilation of used air back to the animal house after filtration should be avoided. In individually ventilated cages (IVCs), specialized primary enclosures and static isolation cages ventilation need to be regulated for optimum air quantity and quality, otherwise the stress levels and heat stress increase very rapidly. Also suboptimum ventilation or ventilation failure increases carbondioxide levels very quickly (3-5% in 1 hour), increasing the toxicity to caged animals. However, if monitored critically, they serve well the purpose of maintaining animal microenvironment and are comparatively economic than centralized cooling systems. Depending on the size of animal house, number of rooms and animals housed the filtration systems should effectively remove 85-95 % of airborn particles. It is more economical to recirculate the filtered air in different rooms of animal house, but should be abstained as it increases the risk of transfer of airborn microbes, pathogens, fomites and zoonoses.

Regular evaluation of air inflow, outflow, air quality (oxygen, carbondioxide and ammonia levels), air pressure, air spread by modern ventilation systems is essential to regulate animal welfare and well being. Vigilance of air temperature and humidity is also required to maintain thermoneutral conditions in the animal house.

Note:

Animal cages or racks should be positioned to optimize air exchange and to avoid draughts for animals.
Concentrations of carbondioxide in IVCs should be less than 5000 ppm

Figure 1. IVCs (Image Source; Orchid Scientific & Innovation India, Pvt Ltd, India) — Figure 1. IVCs
(Image Source; Orchid Scientific & Innovation India, Pvt Ltd, India)

Light

Intensively housed laboratory animals are totally dependent on external illumination for normal circadian rhythms. Light quantity, quality and intensity are important for animal’s natural process and maintenance of physiology, behaviour and reproductive cycles. Light intensity in the animal house should be adequate, for routine house inspections. Photoperiod distribution in animal house should be according to species, age, general condition, pregnancy status and strain of animal. A 12 hour light and dark cycle is routinely followed for rats and mice. For breeding animals this light cycle should be changed to 14 : 10 light and dark, respectively. Time controlled illumination systems can be utilized in animal houses for diurnal and nocturnal species, separately. Rats, especially albino ones are very sensitive to light and develop many afflictions easily. For animals susceptible to phototoxic retinopathy, light should be between 130 and 325 lux in the animal room (at 100-172 cm height). Mostly rats and mice are nocturnal and prefer light intensities between 25-40 lux inside cages. At night times, 18W low pressure sodium lamps or bi-chromatic light, with an average lumen output of 1650 to 1800, is beneficial and does not disturbs the nocturnal activity. In stacking cage model there can be wide variation in the light intensities in animal cages (upto 80 times) at different levels. This should be adequately monitored and light intensity be accordingly regulated, meeting the photoperiodic requirements of the species.

Note:

Light intensities below 60 Lux for pigmented and below 25 Lux is recommended for albino strains.
Flickering light source inflicts stress on animals and hence avoided.

Sound and vibrations

Auditory senses are very well developed in animals and both high and low frequency natural, mechanical or sound from human activities affect the animal behaviour. High decibel sound or very low frequency noise can be potentially deleterious to laboratory animals affecting their behaviour, cognition and immune responses. Similarly, vibrations coming from the machinery should be kept to a minimum in the primary enclosure. A proper distance of the animal house from human quarters and other machines ensures minimum disturbances and display of normal physiological behaviour. Short exposure of animals to sound of 85 dB and chronic exposure to intensities of more than 100 to 165 dB cause noise induced stress and should be avoided. In addition the background noise should be kept below 50 dB in the animal house. Playing of background music has a soothing effect and reduces stress levels in animals.

Figure 2. Factors affecting animal welfare in animal house

(Image Source; Baumans and Van Loo, 2012)

Improvement to consider

Provide adequate space to animals, avoid overcrowding and unnecessary stress. It facilitates proper heat distribution and dissipation, increasing animal performance.
Provide shelter and bedding material to facilitate retreat when disturbed or scared so that animals can exhibit their natural behaviours, be comfortable, maintaining homeothermy.
Ventilated caging system provides better sanitation and control of microenvironment hence should be adopted over static caging system.
Regular cleaning, disinfection and sterilization (with gaseous hydrogen peroxide or chlorine dioxide) of the animal house and cages ensure pathogen free, healthy macro and microenvironment for the animals.
Recirculating ventilation systems must be regularly serviced and calibrated to check the environmental variables like temperature, humidity, THI, air flow and quality.
Bedding or nesting material should be of good quality, have absorptive nature which will help absorb moisture and reduce ammonia production and maintain air quality in animal house.
Unnecessary noise and vibration should be monitored and controlled through soundproof designs and there should be minimum human intervention inside animal house.
Care must be taken to group the animals according to their traits, gender wise or group wise or alone, so that they are comfortable and stress free.
There should be provision of gnawing materials like wood, nylon etc for rats and mice, essential for expression of natural behaviour and physical activity.
Hiding structures and sufficient nesting material be present in cages, so that animals can avoid unwanted exposure to light.
There should be pre installed facility in animal cages to measure the temperature, humidity and ammonia levels.

https://az.research.umich.edu/animalcare/guidelines/guidelines-mouse-and-rat-breeding-and-housing-management

Dr.A.K.Wankar^1*, Dr.P.M.Kekan², Dr.S.N.Rindhe³

^1*Corresponding author, Assistant Professor, Department of Veterinary Physiology, COVAS, Parbhani

² Professor, Department of Veterinary Physiology, COVAS, Parbhani

³ Assistant Professor, Livestock Product Technology, COVAS, Parbhani

References

Alworth LC, and Buerkle SC. 2013 The effects of music on animal physiology, behavior and welfare. Lab Anim Europe. 13(2): 54–61.

Baumans, V., Van Loo, P.L.P. 2012. How to improve housing conditions of laboratory animals: The possibilities of environmental refinement. The Veterinary Journal. http://dx.doi.org/10.1016/j.tvjl.2012.09.023)