Relationship among indicators of pain and stress in response to piglet surgical castration: an exploratory analysis

Multi-dimensional approaches are suggested as advantageous for evaluation of pain and/or stress at piglet castration, but the interpretation of data from such approaches is limited by a lack of understanding of relationships among different types of indicators and associated parameters. This paper used an exploratory approach to evaluate the interrelationships between different physiological, vocal, and behavioral indicators obtained during and after surgical castration of 580 piglets aged 3-4 days. The data, obtained from two experimental studies, were examined by analyses of correlations and by principal component analyses (PCA). Principal components were analyzed in mixed effects models. Each type of indicator (vocalization, resistance movement, saliva cortisol concentration, behavioral response in a social motivation test, behavior in the home pen, reaction to human) mainly contributed to separate principal components in the PCA and showed relatively low correlation coefficients between each other, indicating a variation in the response explained by the indicator types. Even within a type of indicator, specific parameters were, in several cases, found to explain different aspects of the piglet response. Overall, the results point to the importance of careful consideration of the differences existing among indicator types and highlight the need for further methodological development in that domain.