Gaskill, B. N., Stottler, A., Pritchett-Corning, K. R. et al. 2016. He’s getting under my skin! Comparing the sensitivity and specificity of dermal vs subcuticular lesions as a measure of aggression in mice. Applied Animal Behaviour Science 183, 77-85.

Aggression is the leading cause of death in young laboratory mice, representing a major welfare issue. Many of the experimental measures used in traditional aggression research, especially those focusing on territorial aggression (e.g., resident/intruder) are poorly suited to examining dominance or abnormal aggression in the home cage. Scoring of flank and tail wounds by observers is widely used in these experimental paradigms. Scoring external skin wounds is time consuming, subjective, and the constant handling of mice involved can affect experimental outcomes. Here we describe a variety of subcuticular signs of aggression that can be observed during necropsy, and develop a 'Pelt Aggression Lesion Scale' (PALS) for standardized scoring of these signs. Inter-rater and test-retest reliabilities were assessed and were excellent (0.84, and 0.96, respectively). PALS showed significantly greater sensitivity (in terms of detecting unusually aggressive cages) and less error variance than external wound scores. PALS showed convergent validity with external wound scores (i.e. each could predict the other), and also discriminant validity (in that only PALS subscores for the posterior of the pelt, where aggressive biting is primarily directed, predicted external wound scores). Finally PALS shows specificity, in that PALS and its subscores did not generate false positive results when animals with ulcerative dermatitis were examined. Thus PALS is a reliable, sensitive, specific and validated measure of aggressive wounding in mice that avoids many of the confounds of traditional methods, is high-throughput, easy to perform, and particularly well suited to home-cage and welfare-related studies but limited in its use for behavioural management interventions.