Effects of divergent selection upon adrenocortical activity on immune traits in pig

Background The sustainability of farming and animal welfare requires the reconsideration of current selection schemes. In particular, implementation of new selection criteria related to animal health and welfare should help to produce more robust animals and to reduce anti-microbial use. The hypothalamo-pituitary-adrenocortical (HPA) axis plays a major role in metabolic regulation and adaptation processes and its activity is strongly influenced by genetic factors. A positive association between HPA axis activity and robustness was recently described. To explore whether selecting pigs upon HPA axis activity could increase their robustness, a divergent selection experiment was carried out in the Large White pig breed. This allowed the generation of low (HPA lo ) and high (HPA hi ) responders to adrenocorticotropic hormone administration. Results In this study, we compared 23 hematologic and immune parameters of 6-week-old, HPA lo and HPA hi piglets and analysed their response to a low dose of lipopolysaccharide (LPS) two weeks later. At six weeks of age, HPA hi piglets displayed greater red blood cell and leucocyte number including CD8α + γδ cells, cytotoxic T lymphocytes, naive T helper (Th) cells and B lymphocytes as compared to HPA lo individuals. The ability of blood cells to secrete TNFα in response to LPS ex vivo was higher for HPA hi pigs. At week eight, the inflammatory response to the LPS in vivo challenge was poorly affected by the HPA axis activity. Conclusions Divergent selection upon HPA axis activity modulated hematologic and immune parameters in 6-week-old pigs, which may confer an advantage to HPA hi pigs at weaning. However, HPA lo and HPA hi piglets did not exhibit major differences in the parameters analysed two weeks later, i. e. in 8-week-old pigs. In conclusion, chronic exposure to high cortisol levels in HPA hi pigs does not negatively impact immunity.