Given that pigs in modern intensive farming systems encounter a range of stressors, it is vital to gain insights into the pig's resilience, which is the ability to return to pre-stress status, across various environmental factors. The aim of the thesis was to assess whether behavioral responses differed between pigs designated as stress-resilient (SR) or stress-vulnerable (SV). We examined the relationships between resilience or vulnerability to weaning stress and 1) pigs’ behavioral response to an auditory startle test, and 2) pigs’ behavior in the home pen, focusing on their behavioral response to and recovery from weaning stress. In the first study, we conducted a startle test on 7-week-old pigs (n = 52) to evaluate their behavioral responses. The data revealed no connection between the response to the auditory startle test and resilience or vulnerability to weaning stress. In the second study, we focused on observing behaviors (d1 & d4 post-weaning) of focal pigs (n = 52) within their home pens in response to weaning. We found behavioral differences associated with stress resilience. On d1, SV pigs had more non-injurious contact (P = 0.0198) but less lying down behavior (P = 0.018) than SR pigs. On d4, SV pigs showed longer fighting behavior (P = 0.025) compared to SR pigs. Additionally, a significant effect of time on behavioral adaptation patterns was observed. On d1 post-weaning, pigs spent more time fighting (P < 0.001) and exploring (P < 0.001) and showed more frequent non-injurious contact (P = 0.013) and drinking behaviors (P < 0.001) compared to d4. Conversely, on d4, pigs spent more time feeding (P = 0.004) and lying down (P < 0.001) when compared to d1. In summary, this thesis enhances our comprehension of evaluating pigs' welfare through their affective state, behavioral responses to challenging situations, as well as physiological resilience, providing opportunities to further improve pig welfare in the future by targeting management and breeding strategies based on resilience.
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