Including immune-neuroendocrine variables in welfare Studies: is it worth the effort?

F. NICOLAS NAZAR , SILVIA G. CORREA RAUL H. MARIN

Simposio; The fourth Animal Welfare Science Symposium 2019; 2019

Centre of Excellence in Animal Welfare Science

Individual susceptibility to environmental challenges, sometimes overlooked in population level studies, may be one of the reasons underlying a poor/low animal welfare. Safeguarding the five-freedoms has been proposed as a strategy for ensuring good/elevated welfare. This core concept in the area implies that animals should have guaranteed freedom from: i) hunger and thirst, ii) discomfort, iii) pain, injury or disease, iv) freedom to express normal behaviour, and v) freedom from fear and distress. Many concepts on these freedoms such as discomfort, fear, distress, injuries and diseases are evidences of the immune-neuroendocrine (INE) system functioning. This physiological system is quintessentially responsible for registering environmental challenges, processing their information and, orchestrate an appropriate response. The reactions could vary in the organism, covering a wide spectrum of possibilities ranging from local inflammation (injuries) to systemic stress responses (distress). The anatomical substrate of the INE system are four well-known axes: the Hypothalamic-Pituitary-Adrenal axis (underlying the stress response), the Sympathetic-Adrenal axis (involved in immediate fight or flight responses), the Vagus-Cholinergic way (sensing and controlling inflammation in the peritoneal cavity) and the Microbiota-Gut-Brain axis (communicational path starting in the part of the exterior that is internal). Animals may show no obvious indicators of poor welfare, but their differential susceptibilities relies on the INE macrosystem. An example can be given by means of a study performed in poultry species. Immune-neuroendocrine phenotypes (INPs) stand for population subgroups differing in INE interactions. While mammalian INPs have been characterized thoroughly (rats and humans), avian INPs were only recently described in Coturnix coturnix (quail). We characterized INPs in Gallus gallus (a domestic laying hen strain submitted to a very long history of strong selective breeding pressure) and evaluated whether a social chronic stress challenge modulates the individuals? interplay affecting the INP subsets and distribution. After chronic stress, an increment of about 12% in each polarized INP frequency was found at expenses of a reduction in the number of birds with intermediate responses. The observed inter-individual variation suggest that, even after a considerable selection process, the population is still prepared to deal with a variety of challenges. Nevertheless, these results imply that not all birds would respond in the same way to the same challenge. Stress promoted disruptive effects, leading to a more balanced INPs distribution, which represents a new substrate for challenging situations. This new substrate is composed by birds differentially prepared to deal with a) diverse kind of common/expectable challenges such as, vaccination, transport, experimenter presence, as well as b) various unexpected (i.e.: pathogenic) events. This aspect of their physiological characterization would be key in their welfare assessment. INE system could then be considered an indicator of which birds would be prone to welfare negative consequences in different scenarios according to the nature of each challenge.