Fig. 3 |. Environmental considerations for pain testing.

a | Factors in a standard vivarium rodent housing room that may affect pain behaviours. Animal behaviour can be influenced by room characteristics such as humidity, temperature and light cycle or factors such as the pain status of other animals housed nearby. Similarly, factors within the home cage can affect pain behaviours even when animals are tested in a different environment. b | Factors in a standard behaviour testing room that may affect pain measurements. As in the housing room, humidity, temperature, lighting and the presence of injured animals may affect test outcomes in a behaviour room. Stress induced by transport to the testing room, novelty of the testing apparatus, order of testing and accompanying procedures such as manual restraint or injection may also affect pain testing results. However, the presence, identity and experience level of an experimenter may be the largest factor that influences pain behaviours.