Recognizing pain in pigs is a prerequisite for treating it effectively. Unlike companion animals where human-animal bonds facilitate individual observation, pigs in commercial production are observed in groups and behavioural changes may be subtle or masked. Advances in pig pain science have developed practical tools for improving pain recognition.
Pigs, as prey animals, tend to mask signs of weakness including pain — an evolutionary adaptation that makes clinical signs less overt than in some species. Pain behaviors overlap with other states (fear, hunger, illness), and group housing means individual assessment requires deliberate effort. Commercial production pressures can discourage time investment in individual animal assessment.
Facial Action Coding Systems adapted for pigs — the Pig Grimace Scale (PGS) — provide validated, species-specific pain assessment tools. The PGS scores orbital tightening, nose bulge/cheek flattening, ear position changes, and whisker/cheek tension on a 0-2 scale for each feature. Validated against known painful conditions, the PGS provides reliable, objective pain assessment that can be applied from video recordings or direct observation.
Beyond facial expression, validated behavioral indicators of pig pain include:
Cortisol (blood or salivary), substance P, and prostaglandin E2 are validated physiological pain markers in pigs. These require sampling but provide objective, quantitative pain assessment for research and welfare audit contexts. Infrared thermography of pain sites shows promise as a non-invasive monitoring tool.
Translating pain science to production practice requires training stockpeople in practical pain recognition. Simple, laminated observation guides with photo examples of pain indicators can be deployed in pig housing for reference during daily rounds. Pain scoring as part of routine animal inspection — rather than as exceptional assessment — normalizes welfare monitoring.
A practical validation of pain recognition is treatment response — a pig that improves after NSAID administration was almost certainly in pain. This retrospective validation helps calibrate stockperson pain recognition skills in real production contexts, building confidence in pain identification over time.