Social and husbandry factors affecting the prevalence and severity of barbering (‘whisker trimming’) by laboratory mice

Abstract

Barbering—the plucking of fur or whiskers from cagemates or oneself—is a common form of abnormal repetitive behavior in laboratory mice. It is often viewed as a ‘normal’ behavior of particular strains, primarily because it is assumed to represent a dominance behavior. Here, we report on a series of experiments investigating the husbandry and social factors involved in barbering. In Experiment 1, we conducted a large-scale epidemiological study. Barbering was found to be related to a number of environmental factors, including cage design, cage location, cagemate relatedness, and the presence of other barbers in the cage. Thus, instead of barbers suppressing the development of barbering in cagemates, as would be expected if barbers were dominant, the presence of a barber in the cage facilitated the behavior in cagemates. In Experiment 2, we quantified the patterns of hair loss seen in barbered mice. These data confirmed that individual barbers pluck idiosyncratic patterns of fur from their cagemates, and that when there were multiple barbers in a cage the patterns plucked by cagemates were significantly more similar than the patterns plucked by non-cagemates. Thus, barbers appear to be facilitating or learning idiosyncratic patterns from their barbering cagemates. Aspects of these data question the assumption that barbering is a dominance behavior. Therefore in Experiment 3, we directly investigated the relationship between dominance and barbering in C57BL/6J mice. The relative dominance score of a mouse within its cage was unrelated to barbering, and the relative severity of hair loss on a mouse was unrelated to its relative dominance. Barbering, therefore, cannot be considered to be a dominance behavior. Instead, our data indicate that it is most likely a form of abnormal repetitive behavior related to compulsive hair plucking (trichotillomania) in humans. The incorrect assumption that barbering represents an eccentric but benign dominance behavior has allowed the welfare consequences of this behavior to remain unaddressed. Barbering should therefore be considered an important variable both in the assessment of the welfare of individual mice and in experiments addressing the impact of husbandry paradigms upon the behavior and welfare of laboratory mice.