Is homeostatic efficiency a positive aspect of health and well-being?

It has been recognized for more than a century that health entails strength and vitality and is more than the absence of disease. In the 1930s, the capacity of regulatory processes to maintain homeostasis in the face of environmental challenges was proposed as a measure of vitality. More recently, this same capacity has been described as resilience. With growing interest in breeding and managing animals for a better (positive) quality of life it is timely to re-examine vitality and resilience through the lens of homeostatic efficiency. The starting point for considering the impact of environmental perturbations is the nature of the animal – environment relationship. This discussion paper examines the relationship from an ecological perspective that emphasizes the subjective character of environmental perception. The ecological viewpoint recognizes that environmental perturbations provide opportunities as well as challenges to the animal. Processes facilitating acquisition of competence to master environmental perturbations – the attribute described as agency - are described. The characteristic that Walter Cannon and colleagues called homeostatic efficiency is compared with present day concepts of resilience and vitality. The relevance of the term homeostatic efficiency is appraised from the contemporary perspectives of homeorhesis and allostasis. It is suggested that homeostatic efficiency retains utility to describe proficiency of the animal in capturing opportunities and minimizing challenges in everyday life, as well as resilience in adversity. In accord with the biopsychosocial model of health, homeostatic efficiency is a system property of organismal regulation that integrates physiological, immune, cognitive, affective, behavioural, microbiome and social processes. Analyses of deviations from trajectories in outcomes of organismal regulation including milk yield, body weight, egg weight, fibre diameter, and feed intake have attracted attention recently as indicators of resilience. It is suggested that both resilience and vitality influence these outcomes. Better characterization of vitality could help clarify concepts and management of positive health and well-being in animals. A multidisciplinary collaboration to develop complementary definitions of the closely related concepts of vitality, resilience, thriving, flourishing, vigour, physiological reserve, and functional capacity would assist this endeavour.