Project Objectives

• Develop a 3D‑printed cage connector enabling visual, acoustic, and olfactory (VOA) contact between individually ventilated cages (IVCs).
• Quantify stress and well-being in single‑housed male mice under SD3 (no VOA contact) and SD1 (VOA contact) conditions.
• Test the effect of partner identity in VOA contact conditions (e.g, dominant vs. subordinate male, familiar vs. unfamiliar male, female).
• Validate welfare indicators, such as cage‑site preference, testosterone/corticosterone, weight, nest location.
• Evaluate whether the current severity degree classification is appropriate.
• Generate guidance for facilities on best practices.

How This Advances 3Rs Implementation

• Enables a substantial severity reduction for an estimated 9,000 male mice per year at UZH alone, by replacing full isolation (SD3) with VOA contact (SD1).
• Reduces chronic stress and injury by providing a housing option that prevents fighting while maintaining controlled sensory contact.
• Improves scientific reproducibility by minimising confounding variables, such as stress‑related physiological and behavioural changes.
• Offers a scalable refinement tool through freely shareable, 3D‑printed cage connectors that facilities can implement.
• Generates objective welfare metrics that support more accurate assessment of male‑mouse housing conditions.
• Provides evidence that can inform future updates to severity classifications and housing guidelines.

Background

Mice are thought to be a social species, and as such, single housing should be avoided. However, separating fighting male mice and keeping them in single housing until the end of an experiment is current practice. Since most mice are housed in individually ventilated cages (IVCs), this leads to social isolation, and a higher severity degree (SD3). In contrast, single housing with visual, acoustic, and olfactory (VOA) contact is considered a lower severity degree (SD1).

It remains unclear whether single housing with VOA contact is truly superior to single housing without VOA contact, and moreover, whether the contact partner identity makes a difference (e.g, dominant vs. subordinate male, familiar vs. unfamiliar male, female). This project attempts to fill this knowledge gap by testing 3D‑printed cage connectors that provide controlled VOA contact between IVC cages, while quantifying behavioural, hormonal, and hierarchy‑related indicators of stress in mice.