Standardising housing and husbandry

Considerable efforts have been made over the last few decades to standardise the housing and care of laboratory animals. This has been done to try to reduce variability in responses to experimental manipulations and to produce more uniform base-line data. Laboratory animals are housed in standardised caging with standardised types of bedding and fed a standard, well-characterised diet. Room environmental conditions are maintained within prescribed ranges of temperature, relative humidity and number of air changes, and with a fixed light-dark cycle. These factors can also be influenced by the frequency of cage cleaning, and by the use of environmental enrichment, so these practices also require standardisation.

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Cage sizes, floor area per animal, and the environmental conditions required for each species are specified in national legislation (in the UK, within Home Office Codes of Practice ). Since all of these factors can influence experimental outcomes (Teske et al, 20141), this information should be recorded both by the animal facility and individual research workers and should be included in the materials and methods of publications when results are reported (as per the ARRIVE Guidelines ).

Fig. 1 Sudden changes in relative humidity can cause a condition known as ringtail in rats.

It is also important to appreciate that small disruptions to these housing conditions can have significant consequences (Emmer et al, 20182). Entering an animal room during the dark phase of the animals’ photoperiod and switching on the normal room lighting can disrupt the animals’ circadian rhythms, producing effects that persist for days. If animals need observing or examining during this period, then red light sources of illumination can be used. Large changes in environmental conditions can also have a significant impact on the health of laboratory rodents. For example, sudden changes in relative humidity can cause a condition known as ringtail in rats (Fig.1). Excessively high environmental temperatures can cause heat stress to rodents, resulting in death. Because a failure of environmental controls can impact both on the welfare of animals, and the scientific outcome of studies, failsafe systems with backup power, and comprehensive monitoring and alarm systems should be in place.

Although environmental factors may be controlled at the level of the animal room, the environmental conditions within each cage will vary (Toth, 20153). For example, the position of the cage on the rack, or in the room, can alter light intensity. The number of animals in the cage and their levels of activity can alter cage temperature, relative humidity and concentrations of substances such as ammonia. Incorporating this understanding of sources of variability into study design – for example by avoiding housing all animals in one treatment group in one room location, and control animals in another – can help control for this remaining variation.

Next Article : Acclimatisation

Updated on 12th May 2020

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