Estratégias de enriquecimento ambiental para promoção de estados afetivos positivos e desenvolvimento cognitivo de leitões desmamados

Abstract

Intensive pig production systems often provide low environmental complexity, restricting motivated behaviours (exploration/oral manipulation) and potentially compromising welfare. Environmental enrichment is promising for promoting more positive affective states, cognition, and resilience to stress; however, there remain gaps in integrated evidence combining behavioural, cognitive, bioacoustic, and biomarker measures. This dissertation assessed, in a complementary way, the effects of environmental enrichment in piglets through a systematic review (Chapter 1) and a controlled nursery experiment (Chapter 2). In Chapter 1, the review followed PRISMA 2020, with searches in Web of Science and Scopus (2000–2025) and eligibility defined by PICO. Twelve experimental studies were included and, due to methodological heterogeneity, a narrative synthesis was performed. Physical enrichment predominated (≈80%), especially during the nursery and growing phases. Overall, studies reported increased exploration/engagement, reduced aggression and harmful behaviours, and improvements in spatial memory and problem solving; effects on more complex cognitive tasks were variable and sometimes modulated by individual differences (e.g., coping style). The review also highlighted recurring limitations, particularly the limited integration of neurobiological/physiological indicators, reinforcing the need for multimodal approaches. In Chapter 2, 675 nursery piglets were assigned to three strategies: UNI (one continuous object), ALT (one continuous object + a second object alternated weekly), and SIM (three simultaneous continuous objects). A subsample (n=32) underwent an Attention Bias Test (ABT), integrating behavioural measures, bioacoustics, QBA, and biomarkers (hair cortisol, serum serotonin, and serum BDNF). Treatments differed little in the ABT attentional component and space use; differences were concentrated in coping profiles (ALT with more time standing still; SIM with more escape attempts; UNI with more elimination events). Post-threat feeding responses were mainly influenced by the stimulus (ES1 vs ES2), with no consistent treatment effect. The vocal repertoire in the ABT was restricted (no screams/squeals and no clear grunts); ALT showed longer vocalisation time (harsh grunts), but the composite vocal affective-state index did not differ among treatments. In QBA, SIM showed an overall expression consistent with more positive valence. Regarding biomarkers, UNI showed a less favourable post-exposure profile (higher hair cortisol and lower BDNF), whereas ALT stood out as the only treatment with increased BDNF from baseline to post without an increase in hair cortisol. We conclude that enrichment complexity—and especially its temporal dynamics—modulates welfare through partially distinct pathways, and that strategies combining stability with controlled novelty have potential to optimise outcomes in commercial systems.