Pain Assessment in Non-Verbal Animals: Reading the Signs of Suffering

Animals cannot report pain verbally, so researchers and veterinarians use validated grimace scales and behavioural indicators to assess and treat pain across species.

Key Facts

The Mouse Grimace Scale, developed in 2010, scores facial action units including eye squinting, nose bulge, cheek bulge, and ear position to rate pain intensity
Grimace scales have now been validated for rats, rabbits, horses, sheep, pigs, cats, ferrets, and several other species
Lameness scoring systems for cattle and pigs allow observers to rate leg pain severity on a five-point scale with inter-rater reliability
Acute pain in fish is associated with fin clamping, reduced swimming activity, colour change, increased opercular beat rate, and rubbing affected areas
Under-recognition of pain in animals leads to inadequate analgesia; validated pain scales have demonstrably improved veterinary pain management

Welfare Considerations

The development and adoption of validated pain assessment tools is one of the most direct contributions science has made to reducing animal suffering. Before grimace scales, pain in laboratory rodents was routinely under-treated because observers had no reliable way to detect it. Validated tools make invisible suffering visible, enabling treatment. The ongoing development of grimace and pain scales for more species — particularly fish, invertebrates, and reptiles — is a priority welfare science agenda.

What You Can Do

Advocate for mandatory pain assessment training using validated scales in veterinary education
Support research that develops and validates pain scales for currently underserved species
Push for guidelines requiring post-procedural analgesia in laboratory animal protocols
Encourage livestock industry adoption of lameness scoring and pain management protocols
Support organisations that translate pain assessment research into practical veterinary and husbandry guidance