Table 4 Some underlying evidence for the importance of random housing and random outcome assessment

Lighting

Light exposure varies with respect to rack location and position of cages within the rack

[27, 28]

Small differences in light intensity have been associated with reproductive and behavioral changes

[27, 29, 30]

There can be a four-fold difference in light intensity between cages at the top or bottom of a rack

[18]

Temperature

Temperature in animal room at 1.5 m can be 3-4˚C higher than at 0.5 m

[18]

Cage temperature varies with group size

[18]

Cage temperature varies with height of placement within the rack (top rack 5˚C warmer than bottom rack)

[18, 31, 32]

Small changes in temperature can influence metabolic rates and toxicity

[27, 31, 33]

Random outcome assessment

Circadian rhythm

Periodic/circadian variations in lipid metabolism, neurotransmitter levels, pharmacokinetic effects, etc.

[34–37]