Interação entre complexidade ambiental e aditivos melhoradores de desempenho na modulação do medo e da ansiedade em frangos de corte

Abstract

Welfare in poultry production, previously centered on the absence of disease and physical stress, has come to recognize avian sentience and the importance of affective mental states. In the face of the challenges of intensive systems, strategies to mitigate negative emotions and mental states, such as fear and anxiety, become essential. In this context, environmental enrichment and the use of additives, such as probiotics, stand out as strategies to promote welfare. This dissertation evaluated the use of these strategies in the modulation of fear and anxiety in broiler chickens and is structured into two chapters: Chapter I – a systematic review aimed at evaluating the effects of environmental enrichment on fear and anxiety in fast-growing broiler chickens, following the PRISMA 2020 guidelines. Twenty-two experimental studies were included that investigated different forms of environmental enrichment, such as physical structures, sensory stimuli, occupational and feeding resources. Most studies focused on the assessment of fear, mainly through the tonic immobility test, while anxiety was investigated in a limited number of studies, concentrated in recent years, using the attention bias test. In general, enrichments that provided functional refuge, biologically relevant stimuli, and greater environmental control showed the greatest potential to reduce negative emotional states in birds. In contrast, isolated interventions or those of low relevance to the birds showed limited or temporary effects. The results indicated that environmental enrichment, when functionally designed and aligned with the behavioral needs of the strain, can act in the modulation of fear and anxiety, improving the emotional welfare of broiler chickens. Chapter II – an experimental study aimed at evaluating the effects of the interaction between performance-enhancing additives and environmental complexity on the modulation of mental state (fear and anxiety) in broiler chickens. A total of 1,440 oneday-old chicks (Ross 308 strain, 39.26 ± 0.51 g) were used, distributed in a randomized block design, in a 3×2 factorial arrangement, considering additives (probiotic × antibiotic × negative control) and environmental complexity (high × low), totaling six treatments with eight replicates each. Serum serotonin concentration was evaluated as an indirect marker of emotional regulation. Acute fear was assessed using the tonic immobility test and anxiety using the attention bias test. The results showed that serum serotonin was influenced by the type of additive, with higher concentrations in birds receiving antibiotics and an intermediate effect for those receiving probiotics as performance enhancers. The tonic immobility test showed no significant effects, indicating low sensitivity to detect emotional changes under the evaluated conditions. In contrast, the attention bias test proved to be more sensitive, revealing effects of additives, environmental complexity, and their interaction. The association between antibiotic and high environmental complexity promoted lower levels of anxiety, while the probiotic maintained an intermediate effect. Thus, fear and anxiety are modulated in distinct ways, and their assessment requires the combination of physiological, behavioral, and cognitive indicators, reinforcing the importance of emotional welfare in management strategies and antibiotic replacement.