Impact of Bedding Volume on Cage Microclimate and Behavior in 129SV and Desmin-Knockout (Des-/-) Mice

Standard laboratory housing often restricts the expression of natural behaviors in rodents, raising concerns regarding animal welfare and the translational value of experimental data. The current study investigated whether increasing cage bedding volume functions as an effective, low-impact environmental enrichment strategy that enhances welfare without confounding physiological parameters. An in-depth analysis was conducted comparing the effect of Deep Bedding (DB; 1600 mL) versus Normal Bedding (NB; 400 mL) on the microenvironment, physiology, and behavior of wild-type (129SV) and desmin-knockout (Des-/-) mice. Results demonstrated that deep bedding acts as a significant environmental buffer, effectively decoupling intra-cage temperature and humidity from ambient room fluctuations. While physiological parameters, including body surface temperature, body weight, and food intake, remained stable across bedding conditions, behavioral analysis revealed a robust upregulation of species-specific fossorial activities, such as digging and burrowing, in the DB group. This suggests a beneficial "bioenergetic reallocation" where energy is directed toward natural behaviors rather than thermal stress responses. Furthermore, deep bedding significantly improved cage hygiene through the mechanical sequestration of waste. These findings indicate that deep bedding serves as a multifactorial refinement strategy that supports animal welfare and hygiene without increasing experimental variability, proving safe even for physiologically sensitive models like Des-/- mice.