Genetic Analysis of the Response to ACTH in Pigs, Relationships with Robustness Traits

The hypothalamic-pituitary-adrenocortical (HPA) axis is a major component of the biological mechanisms of adaptation. The HPA axis activity and function are strongly influenced by genetic factors. The present experiments were designed to test the hypothesis that genetic selection for a more active HPA axis could improve robustness of pigs. Experiments were done with Large White purebreds. We first confirmed that the cortisol response to ACTH is highly heritable (h² = 0.68) in this population and could be used for carrying out a divergent selection experiment. As early as the second generation, large differences were found in the selection trait (cortisol post-ACTH: 84.8 vs 127.5 ng/mL in the low and high line respectively) but also in reproduction traits (35 % more sperm per ejaculate, 11 points higher farrowing rate and 1 more piglet per litter in the high line), with minimal changes in body weight and growth, confirming our initial hypothesis. We also showed that the biological effects of cortisol are strongly influenced by CBG levels, the carrier protein of cortisol in plasma, and it is well established that receptors and post-receptor mechanisms are critical in cortisol efficiency. All these processes are under genetic control, so that a system genetic approach is necessary to better improve robustness through selection of HPA axis activity and function. Grants from Agence Nationale de la Recherche (ANR-12-ADAP-0008) and INRA, Animal Genetics Division.