Less experienced observers assess piglet castration-induced acute pain differently than experienced observers: A pilot study

Behavioral pain scales have been helpful for standardized swine pain assessment. However, it is still unknown if observers’ experience influences the scale score. We conducted a pilot study to investigate how three different levels of swine experience influenced how observers scored castration pain in piglets using Unesp-Botucatu Pig Composite Acute Pain Scale (UPAPS). We used a database from UPAPS scores from pigs undergoing surgical castration in a previous study. Scores were attributed by six observers with Little to no experience (n = 2), Some experience (n = 2) and Extensive experience (n = 2). Reliability was estimated using the intraclass correlation coefficient, agreement was investigated by Bland-Altman analysis, predictive capacity was estimated using the area under the curve (AUC), and statistical differences were tested using a regression model. We found that intra-experience levels reliability were satisfactory (Little to no: 0.72, Some: 0.81, Extensive: 0.84), but inter-experience reliability was lower (0.42). Little to no experience observers had poor agreement with other observers, with a bias toward underscoring UPAPS (bias of 0.94 vs. Some, 1.17 vs. Extensive). Predictive capacity was similar between all observers (AUC, Little to no: 71.94%, Some: 76.10%, Extensive: 79.09%, p > 0.05). Regression model confirmed underscoring of Little to no experience observers (mean ± standard error; Little to no: 1.09 ± 0.14; Some: 2.02 ± 0.23; Extensive: 2.25 ± 0.22; p