Barbering, a behavior frequently observed in group-housed laboratory mice, is a repetitive action where a mouse plucks the fur or whiskers from itself or its cage mates. This activity is classified as an abnormal repetitive behavior, or stereotypy, and is comparable to human compulsive hair-pulling (trichotillomania). Barbering is a significant welfare concern for the animals, resulting in visible hair loss for the victim or sometimes the barber itself. While common in specific laboratory strains, it is generally not seen in mice living in their natural environment.
Identifying the Signs of Barbering
The clearest indication of barbering is the appearance of a mouse with distinct, localized patches of missing fur. This hair loss results from the precise removal of hair shafts close to the skin, not from skin disease or parasites. A key differentiator is the pattern of hair loss: a barbered mouse will have smooth, intact skin underneath the bald patch, unlike the inflammation or scabbing seen with fighting injuries.
The location of the hair loss often identifies the barbering style. “Hetero-barbering,” where one mouse plucks a cage mate, typically results in hair loss around the muzzle, eyes, and the dorsal surfaces of the head and neck. The most characteristic sign is the absence of whiskers (vibrissae), which are vital sensory organs for the mouse. Conversely, “self-barbering” results in hair loss on the chest, belly, genitals, and the inner or outer surfaces of the forearms.
Identifying the behavior requires distinguishing between the “barber” and the “victim.” The mouse performing the plucking is often completely unaffected, while the victim exhibits the hair loss. Historically, the barber was assumed to be the dominant mouse, but recent studies suggest that barbering is not directly linked to social dominance. A single barber can be responsible for the hair loss on multiple cage mates.
Social and Environmental Causes
Barbering is a complex behavior driven by genetic predisposition and external pressures, classifying it as a stress-evoked response. Certain inbred strains, such as C57BL/6, 129SVE, and C3H, show a genetic predisposition for this behavior. Females are statistically more likely to become barbers than males, with breeding females exhibiting the behavior more frequently than non-breeding stock mice.
A major driver of barbering is environmental deprivation, specifically a lack of enrichment that leads to chronic boredom. In the confined, simplified conditions of standard laboratory housing, mice may develop stereotypies like barbering as a coping mechanism for the stressful environment.
Stress factors like high stocking density, frequent handling, or persistent noise can elevate stress levels, strongly associated with the onset of barbering. The social structure can still affect the behavior; the presence of a barber in a cage can facilitate the behavior in other cage mates, indicating a potential element of social learning. The behavior is also associated with oxidative stress, a physiological condition implicated in other compulsive disorders.
Strategies for Stopping the Behavior
Intervention focuses primarily on modifying the environment to reduce stress and provide outlets for natural mouse behaviors. The most effective strategy involves comprehensive environmental enrichment, especially when introduced early in the mice’s lives. Providing materials that allow for nesting, such as cotton squares, shredded paper, or specialized nesting pads, is highly beneficial as it allows them to build complex structures.
Introducing items that encourage exploration and physical activity can also help reduce the repetitive behavior. Simple enrichments like small tunnels, plastic containers, or chew toys give mice an opportunity to engage in complex, goal-oriented behaviors. Studies show that starting enrichment programs when mice are first group-housed can dramatically reduce the prevalence of barbering.
Managing the social dynamics of the group is another practical step, particularly for severe cases. If a specific “barber” mouse is identified, temporarily separating that individual from the victim allows the victim’s fur to regrow and prevents further injury. Since permanent separation can introduce new stress, re-grouping should be considered while carefully monitoring the new social dynamic. If the behavior persists despite environmental changes, dietary supplements or veterinary consultation may be necessary. For instance, the antioxidant N-acetylcysteine has shown promise in treating compulsive hair-pulling.