Social conflict in laboratory rodents as a cause of pain and distress

Paul F. Brain
School of Biological Sciences, University of Wales Swansea, Swansea, SA28PP, UK.

There is a substantial literature on social conflict in laboratory mice (the most heavily utilised of the laboratory vertebrates). Males show fighting and threat most commonly but some forms of conflict involving females (e.g., attacks by lactating animals on strange male intruders) can actually be more damaging. The influences of genes, housing density/complexity and familiarity/experience on the propensity for this behaviour are reviewed. The stressful consequences of fighting appear associated with complex endocrine disturbances leading, in addition to injury (from superficial bites to severe damage), to suppressed weight gain, reproductive impairment and lowered disease resistance in some subjects. The levels of agonistic behaviour of mouse stocks should be routinely assessed (especially in the 'dark' periods of lighting cycles when people do not generally observe them) and that attempts at 'environmental enrichment' must be carefully monitored to prevent their inadvertently intensifying agonistic behaviour (some animals use added items in their territorial displays). There is thus ample evidence that intraspecific fighting can be a real and substantial cause of social stress in male (especially) and female mice. Such stress not only impairs the welfare of these laboratory animals but introduces unwanted experimental variability in subjects. obviously, the levels of potential fighting in particular stock should be routinely assessed and techniques used to minimize the levels of such activity. It is particularly important to know what the animals are doing in the dark phases of their lighting cycles and to ensure that 'enrichment' attempts do not inadvertently intensify the problems caused by social conflict.
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