Psychometric validation of the Short Form of the Unesp-Botucatu Pig Composite Acute Pain Scale (UPAPS-SF) for assessing pain in piglets following surgical castration.

Piglets' surgical castration is a painful procedure leading to behavioural alterations that can be used to diagnose pain. The Unesp-Botucatu Pig Composite Acute Pain Scale (UPAPS) is a validated scale widely used in research. Previous refinement studies have proposed that UPAPS could be shortened to only presence/absence of five behaviours. Therefore, our aim was to test the psychometric properties and validate the Short Form of the UPAPS (UPAPS-SF) for diagnosing acute pain in piglets undergoing surgical castration. Forty-eight 2-8 days-old piglets were video-recorded 24h before, immediately after, and 24h after surgical castration. Prior to castration, 24 piglets received transdermal flunixin meglumine (Flunixin group) and 24 piglets did not receive analgesia (Control group). Four-minute videos were analysed by six trained observers using the UPAPS-SF. The intraclass correlation coefficient showed high repeatability (0.86-0.91), and good to very good reproducibility (0.72-0.83). Multiple correspondence and confirmatory factor analyses supported a unidimensional scale structure. Responsiveness and construct validity were confirmed by increasing scores immediately post-castration, and lower scores in Flunixin group vs Control group (p < 0.05). Item-total correlations ranged from 0.67 to 0.85. Internal consistency was high (Cronbach's alpha = 0.80; McDonald's omega = 0.93). The optimal cut-off point (≥ 2/4) yielded 86.30% sensitivity and 94.64% specificity. The area under the curve was 92.96%. Wags tail was removed during refinement, resulting in a four-behaviour scale: Activity, Interaction, Head down and Sits with difficulty. In conclusion, UPAPS-SF is a reliable, valid and practical tool for diagnosing acute pain in piglets undergoing surgical castration.