# Environmental Exposure to the Common Trunk of Mammalian Appeasing Pheromone Modulates Social Behavior and Reduces Fight Wounds in Male Mice

## TL;DR

Exposure to a synthetic mammalian appeasing pheromone reduces aggression and injuries in male mice, improving their welfare in laboratory settings.

## Contribution

The study demonstrates that a synthetic pheromone can modulate social behavior and reduce aggression in group-housed male mice.

## Key findings

- Mice exposed to the pheromone had fewer injuries and engaged in more non-violent communication.
- Treated mice showed higher serotonin levels, linked to reduced aggressiveness.
- The protective effects were strongest during the early stages of group housing.

## Abstract

Aggression among male laboratory mice housed together is a common problem in research facilities, often leading to injuries, stress, and the need to separate or cull animals, which negatively impacts their welfare and the reliability of scientific results. This study investigated whether exposure to a synthetic version of a chemical signal, called mammalian appeasing pheromone, could reduce aggression and modulate social behavior in male mice. We assessed a range of behavioral tests, injury rates, and blood parameters related to stress and aggression. While behavioral tests showed only limited differences, animals treated with the pheromone displayed clearer signs of improved welfare: they had fewer injuries, engaged more in non-violent communication behaviors, and showed changes in serotonin levels associated with aggression control. The protective effects were most evident during the early stages of group housing. Our findings suggest that this non-invasive treatment could reduce aggressive behavior in group-housed male mice, improving animal welfare in laboratory settings and potentially shaping better housing strategies in both research and breeding environments.

Aggression among group-housed male laboratory mice poses significant challenges for animal welfare and scientific outcomes. Semiochemicals, such as mammalian appeasing pheromones, have shown potential in modulating social behaviors in various species. This study aimed to evaluate the effects of a synthetic Common Trunk (CT) of mammalian appeasing pheromone on social behavior, aggression, and welfare indicators in adult male mice. Specific Pathogen Free (SPF) male RjOrl:SWISS mice (8–12 weeks old) were housed in open-top cages and exposed via environmental passive diffusion to either a 2% synthetic CT pheromone formulation or a placebo (excipient only). Behavioral tests included the Elevated Plus Maze (EPM) and the Resident–Intruder (RI) test. Clinical welfare assessments and hematobiochemical analyses were also performed. Behavioral testing revealed minimal differences between groups, except for—in animals exposed to the CT—significantly fewer unsupported rearings, both in number (p = 0.0284) and duration (p = 0.0184), suggesting reduced vigilance (EPM Test) and shorter upright posture durations (p = 0.0031), a behavior linked to social signaling during conflict (RI test). Welfare assessments and risk-based analyses indicated that mice exposed to the CT of the appeasing pheromone displayed more agonistic but less violent confrontations, with fewer visible lesions. The protective effect was most pronounced during early group housing of unfamiliar adult males, with significantly fewer injuries in treated mice during the first (p = 0.0215) and second week (p = 0.0329). Treated mice also showed higher serotonin levels (p = 0.0295), suggesting reduced aggressiveness in line with observed behavioral outcomes. Exposure to the CT appeared to improve social dynamics and reduce escalation of aggression in male mice, supporting its potential as a refinement tool in laboratory housing practices.