Pigs behind the technology : individual activity monitoring to assess resilience in pigs

Abstract

Resilience is a highly relevant trait in pigs, as it may influence their welfare. Resilience is defined as the capacity to be minimally affected by and recover swiftly from a challenge. Resilience is, however, difficult to measure directly. A potentially relevant proxy measure for resilience is activity, as activity patterns deviate under challenging circumstances. The aim of this thesis was to explore novel technologies to measure activity changes as a proxy for resilience. Accelerometers and computer vision were implemented to measure activity following a sickness challenge. Increased root mean square error (RMSE), reflecting variation, and skewness in accelerometer activity three days after infection with porcine reproductive and respiratory syndrome virus (PRRSV), and changes therein compared with pre-infection levels, were associated with higher probability of morbidity and mortality, respectively. Pigs housed in an alternative system comprising group farrowing, delayed weaning, more space and enrichment materials (AHS) appeared to be more resilient and experienced less chronic stress than conventionally housed pigs (CONV), as they were less affected by and/or recovered faster from a transport and a lipopolysaccharide (LPS)-induced sickness challenge, showed less cortisol accumulation in hairs and a lower variance in weight gain. Limited housing effects were found on characteristics of the LPS-induced activity dip, but AHS pigs showed higher baseline activity than CONV pigs. Relationships between the physiological changes and the activity dip in response to the LPS challenge were limited. Hence, sickness-induced changes in activity patterns cannot simply be used as a substitute of physiological data. This does not imply that the activity decrease in itself is not an important aspect of the sickness response which may have consequences for animal health. Taken together, activity patterns and deviations therein are, supplementary to physiological variables, promising indicators of (loss of) resilience in pigs. Overall, the results of this thesis contribute to the biological understanding of resilience and future enhancement of animal welfare.