Resilience indicator traits in chickens: a systematic review

The resilience of an animal is its ability to cope with short-term disturbances, including those caused by pathogens, through response and rapid recovery to its original state. Here, a systematic literature review was conducted to identify resilience indicators that have already been studied and implemented for chickens, along with the contexts or specific stressor under which they were examined. The literature review was based on predefined search criteria, including 'chickens' as the population of interest, a stress exposure description and the term 'resilience'. Screening of titles and abstracts was assisted by the AI-based tool ASReview, followed by full text screening and analysis. According to selection criteria, we finally identified 33 relevant publications on resilience indicator traits used in chickens. Two of these studies analyzed chicken resilience based on routinely collected big data, while the remaining majority were small or medium scale studies and trials. The majority of the studies focused on immune (n = 13) or thermal challenges (either before or after hatching; n = 14), especially heat stress. A variety of resilience indicators were studied; most studies investigated production- or performance-related parameters and/or immunity or disease-related parameters. About half of the studies included genetics- or gene expression-related indicators. Investigation of behavioral indicators of resilience - other than feed intake - was limited (n = 4). Overall, this systematic review provides a comprehensive overview of published resilience indicators in chickens and highlights gaps for future research. This review also revealed a need for the controlled use of terms like resilience, robustness, resistance, tolerance or adaptability, and the relevance of assessing the phase of recovery after a short-term disturbance in the context of resilience.