Recognising and assessing pain in pigs is fundamental to welfare management. Unlike in companion animals where owners notice behavioural changes, pigs in commercial settings are often observed by stockpeople who may see hundreds of animals daily — making validated, efficient pain assessment tools particularly important.
Pain from disease, injury, or painful procedures causes suffering, impairs production, and represents a welfare obligation. Unrecognised or untreated pain is a preventable welfare failure. Common painful conditions in pigs include: joint disease (swine arthritis), lameness from foot lesions, respiratory disease (pleuropneumonia), intestinal disease, tail biting injuries, fighting wounds, and pain following management procedures (castration, tail docking). Assessment tools enable evidence-based pain management decisions.
Validated grimace scales have been developed for pigs, based on the same principle as human infant pain scales — assessing facial action units associated with pain. The Pig Grimace Scale assesses: orbital tightening (squinting of the eye), cheek tightening, ear position (flattening or rotation), snout shape, and nose line changes. Validated against known painful conditions, the scale enables rapid pain scoring based on facial observation. Training is required for reliable scoring, but the scale provides a structured framework for pain recognition.
Behaviour provides important pain information. Pain-related behaviours in pigs include: abnormal postures (back arching, weight shifting, reluctance to bear weight on a limb), reduced activity and social interaction, increased vocalisation (particularly during handling or movement of painful areas), aggression when painful areas are touched, altered feeding behaviour (reduced feed intake, reduced time at feeder), and abnormal gait. Regular observation of these indicators during routine stockperson rounds enables detection of painful conditions.
Lameness scoring is a critical pain assessment tool for pigs, given the prevalence of lameness (affecting 5-20% of sows in many herds) and its associated welfare burden. Validated locomotion scoring systems (0-5 or 0-3 scales) assess gait abnormality, weight bearing, and willingness to walk. Regular systematic lameness scoring (weekly for sows, at routine handling opportunities for growers) enables early detection and treatment. Tracking lameness prevalence over time monitors welfare trends.
Physiological pain indicators including cortisol, acute phase proteins (haptoglobin, serum amyloid A), and substance P can be measured in blood or saliva samples. These provide objective evidence of stress and pain but require sampling (causing additional stress) and laboratory analysis, limiting their practicality for routine clinical use. They are valuable in research settings for validating behavioural pain scales and assessing analgesic efficacy.
Pain assessment tools have no welfare value unless they trigger appropriate action. Stockpeople trained to recognise pain signs must be empowered to either treat (administering licensed NSAIDs under written veterinary authority) or escalate to veterinary attention. Written pain management protocols specifying which drugs, at what doses, for which conditions, and with what monitoring requirements provide the framework for consistent, welfare-centred response. Integrating pain assessment into routine monitoring checklists embeds it as a standard management activity rather than an exceptional response.