Resilience Metrics in Pigs: How Novelty and Environmental Complexity Shape Affective State and Neurobiological Outcomes.

This study evaluated whether the complexity and temporal dynamics of environmental enrichment during the nursery phase are associated with piglets' threat-related responses and affective state using a multimodal approach. We combined an Attentional Bias Test (ABT) with bioacoustic measures, Qualitative Behavior Assessment (QBA), and biomarkers (hair cortisol and serum BDNF). In a commercial nursery setting, 675 piglets were allocated to three treatments: UNI (single continuous item: chains), ALT (chains plus an additional object rotated weekly), and SIM (continuous simultaneous provision of multiple objects). A subsample of 32 piglets underwent the ABT (UNI, n = 10; ALT, n = 11; SIM, n = 11). Most ABT measures related to threat-directed attention and space use showed no detectable treatment differences under the present protocol, and feeding latency was affected by stimulus exposure but not by treatment. In contrast, treatments differed in coping-related responses: UNI showed a higher frequency of excretions, ALT showed a longer standing-inactive duration, and SIM showed more escape attempts. Vocalizations were restricted to harsh grunts, with ALT showing longer harsh-grunt duration and higher total vocal output. QBA and biomarkers further differentiated treatments: SIM showed calmer/less tense expressive profiles, whereas UNI showed higher post-exposure hair cortisol and lower serum BDNF than the more complex conditions. Overall, enrichment-related differences were more consistently detected in coping-related behavior, QBA, and biomarkers than in ABT attentional measures, suggesting that enrichment implementation (stable vs. rotational) shapes partially dissociable behavioral and physiological adaptation profiles, and that both more complex strategies showed a more favorable biological profile than UNI.