Pain Assessment in Laboratory Mice: Improving Welfare Through Better Recognition

Mice are the most widely used laboratory animal species globally, and improving the recognition and treatment of pain in mice is one of the most impactful welfare improvements available to biomedical research institutions.

Key Facts

Mice account for approximately 60-70% of all laboratory animals used in research globally
The Mouse Grimace Scale, developed in 2010, enables reliable pain assessment using facial action units
Mice display pain through orbital tightening, nose and cheek bulging, ear position changes and whisker changes
Pain goes unrecognised and untreated in a significant proportion of mice undergoing painful procedures
Analgesics are underprescribed in mice partly due to concern about confounding experimental results
Studies show that untreated pain suppresses immune function and alters behaviour in ways that confound data more than analgesics do
Procedural pain from surgical procedures, tumour models and inflammatory models is among the most common unaddressed pain in mice
Training researchers to use the Mouse Grimace Scale significantly improves pain recognition and treatment rates

Welfare Considerations

Untreated pain in laboratory mice represents both a welfare failure and a scientific problem. Mice in pain show altered physiology, behaviour and immune function that confounds experimental data, meaning the failure to treat pain is counterproductive even from a purely scientific standpoint. Cultural norms in some laboratories assume mice do not experience pain as intensely as larger mammals, despite clear evidence of comparable nociceptive systems. The Mouse Grimace Scale provides a validated, accessible tool for pain assessment that does not require specialist training. Implementation of routine pain assessment and pre-emptive analgesia protocols is achievable and evidence-based.

What You Can Do

Support research institutions that commit to routine pain assessment and treatment for laboratory mice
Advocate for incorporation of the Mouse Grimace Scale into standard laboratory animal welfare training
Encourage research funders to require evidence of pain management protocols in grant applications
Support the development of non-animal alternatives to replace painful mouse models
Raise awareness among researchers that analgesic treatment improves rather than compromises data quality
Back regulatory requirements for pre-emptive analgesia in procedures classified as moderate or severe severity