The sheep grimace scale (SGS) is a validated pain assessment tool that uses facial expression changes to identify pain in sheep. Its development and use represents an important advance in farmed animal welfare assessment.
The development of species-specific pain grimace scales represents a paradigm shift in how we understand and assess farm animal pain. For sheep specifically, the SGS has provided scientific validation for what welfare scientists long suspected but could not easily demonstrate: that stoic behaviour in prey species masks significant pain that was routinely ignored in farming practice. The finding that facial expression provides reliable, repeatable pain indicators — even in animals that do not vocalise pain — has important implications for pain management requirements. Regulatory responses to SGS evidence have been gradual but positive: the increasing restriction of non-analgesic husbandry procedures draws on the scientific evidence that grimace scales have made incontrovertible. The broader significance is methodological: the grimace scale framework, originally developed for laboratory rodents, has now demonstrated that subjective pain experience can be assessed objectively across a wide range of species, fundamentally changing the evidence base for animal welfare policy.