The intricate relationship between stress and animal welfare: from historical perspective to new avenues

We discuss the intricate relationship between the evolution of the concept of stress and the development of the concept of animal welfare. After a brief review of the main concepts of animal welfare, we analyse important steps in the evolution of the concept of stress, starting from the mechanistic approach of the General Adaptation Syndrome to the recent integrative allostatic theory. We show how, over time, each concept of stress has informed the development of the concept of animal welfare. We discuss the role of emotions and affective states in the response of animals to challenges and how psychological stress is integral to the welfare of animals. Lastly, we discuss briefly the potential role of the gut-brain axis in both the concept of stress and the concept of welfare.