Module 05 - Research Issues

Physical and Environmental Factors

Room Temperature

Small laboratory animals respond to temperature variations by changes in behaviour (e.g., shivering, huddling) and metabolic rate (including increased food consumption if they require more body heat production). These changes could affect several metabolic processes including drug metabolism. Daily animal room temperature fluctuations should therefore be limited (by good heating/ventilation design) to +/- 2^oC. Daily temperature fluctuations should be monitored and recorded. For some studies it may be necessary to measure cage (microclimate) parameters, and not just room environment.

Relative Humidity

Animal room relative humidity should be maintained at 55%+/-15%. This is important for several reasons: for the welfare/comfort of the animals (and the staff); for minimising disease spread by reducing the viability of airborne microbes; for allergen reduction. Prolonged relative humidity (RH) of less than 40% can cause ringtail in young, unweaned rats, and result in respiratory irritation.

Ringtail in a young rat.

Ventilation

Recommended air exchange rates in animal rooms are 15-20 air changes per hour. Such high rates, compared to human office or laboratory spaces, are necessary to remove animal generated heat, ammonia, carbon dioxide, and airborne particles (dust and allergens). Static microisolator cages may contain high levels of ammonia and carbon dioxide despite good ventilation rates in the room itself. Air pressure gradients from animal rooms to corridors, or between zones in an animal facility are also important for containment of micro-organisms.

Within a laboratory animal holding room there can be significant variations in ventilation, and levels of ammonia and CO₂, as well as air flow. Randomising the location of animals in different treatment groups in a rack or in the room may help to avoid bias in the results due to these factors

Lighting

The lighting cycle for the animals has several aspects; the day/night cycle, the intensity of the lights, and the wavelength. Timer control of day/night cycle is necessary to maintain a consistent diurnal rhythm in the animal's metabolic state. The intensity and wavelength are also important to animals. Albino rodents in particular experience retinal damage when room light intensities are above 300 Lux. 

The sudden onset of lights in the morning affects some hormone levels - effects that may last for several hours. The use of dusk/dawn lighting systems, which gradually change light intensity between dark and light phases is encouraged.

For studies where the light levels might influence the research results, randomising the location of animals in different treatment groups on a holding rack may be useful in avoiding a light-induced bias in the results obtained. 

Light "Pollution" Can Alter Tumour Growth Rates

In a study reported by Dauchy, et al., in the journal Laboratory Animal Science (1997), light contamination during the dark phase significantly altered the growth of a tumour (Morris hepatoma) in rats and changed some metabolic factors. In this experiment, the light "pollution" was a very low light level from a light in a hallway shining through a window into the animal room. This study reinforces the need to examine all factors that might cause variability, including the actual levels of light in the animal room, to ensure that the results obtained are meaningful. 

Noise

The impact of noise on the behaviour or responses of laboratory animals in biomedical research has received too little study. The fact that loud "buzzer" noises may induce seizures in young rodents (this has been used to create a model of audiogenic seizures) is well known. Both intensity and sound frequency are important. Rodents and some other animals are particularly sensitive to ultrasonic frequencies, ones that we may not even be aware of since they are beyond the range of the human ear. Low frequency and other noises, for example from nearby construction, may also disturb the animals.

Feeds and Water

Unless otherwise specified by the investigator, SOPs in most animal facilities include provision of regular (perhaps certified) feeds. Water is usually municipal water with perhaps some treatment in the animal facility. If special dietary or water requirements are needed for the research project, the researcher must inform the animal facility management and laboratory animal technical staff.

Laboratory Animal Bedding

Unless otherwise specified by the investigator, SOPs in most animal facilities include provision of regular bedding materials for that facility. Any special bedding requirements have to be specified by the principal investigator.

The phenomenon of resins in softwood bedding (e.g., cedar shavings) activating some of the hepatic enzyme systems (P450 enzymes) is well known. This may complicate results if the experimental outcome is related to hepatic enzyme activity.