Although environmental conditions in all facilities will meet national standards, they may nevertheless vary from each other. Type of caging, bedding and diet, as well as factors such as light/dark cycle, the frequency of cage cleaning etc. can all differ. These factors may also vary between different areas within a facility, for example between a barriered breeding unit, and a room housing animals undergoing studies.
Transferring animals onto study will almost invariably result in changes in the social group, and possibly trigger aggression as social hierarchies are adjusted. All of these factors will result in changes in the animals’ physiology, for example in endocrine responses, immune function, and behaviour (Montonye et al, 20181). It is important that these changes are allowed to stabilise before commencing any experimental manipulations, and a period of 7-14 days is usually recommended (Conour et al, 20062).
Further disturbances to the animals’ physiology caused by stress responses can be reduced by habituation to handling and any restraint or other procedures that will be required during the study. Adaptation not only results in less variable responses to experimental manipulations but also is good for animal welfare, by enabling animals to adapt to these stressors before being subjected to study-related stressors. More on this topic is given in articles on Recognition of Pain, Suffering and Distress.