GrimACE: automated, multimodal cage-side assessment of pain and well-being in mice

Pain and welfare monitoring is essential for ethical animal testing, but current cage-side assessments are qualitative and subjective. Here we present the GrimACE, a fully standardized and automated cage-side monitoring tool for mice, the most widely used animals in research. The GrimACE uses computer vision to provide automated mouse grimace scale (MGS) assessment together with pose estimation in a safe, dark environment. We validated the system by analyzing pain after brain surgeries (craniotomies) with head implants under two analgesia regimes. Human-expert and automated MGS scores showed very high correlation (Pearson's r = 0.87). Both expert and automated scores revealed that a moderate increase in pain can be detected for up to 48 h after surgeries, but that both a single dose of meloxicam (5 mg/kg subcutaneuously) or three doses of buprenorphine (0.1 mg/kg) + meloxicam (5 mg/kg subcutaneuously) provide adequate and comparable pain management. Simultaneous pose estimation demonstrated that mice receiving buprenorphine + meloxicam showed increased movement 4 h after surgery, indicative of hyperactivity, a well-known side effect of opioid treatment. Significant weight loss was also detected in the buprenorphine + meloxicam treatment group compared with the meloxicam-only group. In addition, detailed BehaviorFlow analysis and automated MGS scoring of control animals suggests that habituation to GrimACE is unnecessary, and that measurements can be repeated multiple times, ensuring standardized postoperative recovery monitoring.