This experiment had the objective to analyze responses to various breeding challenges in the third generation of selection of two lines of pigs genetically selected on the basis of plasma cortisol levels measured one hour after injection of ACTH. This test allows to objectify the activity level of the hypothalamic-pituitary-adrenal (HPA) axis, a major neuroendocrine system of the stress response. The results presented here show that the post-weaning growth rate was significantly lower in the high line, although the two lines had the same overall growth rate throughout their productive lives. The effects of a prolonged exposure to high temperature (30°C) and of group mixing stress prior to slaughter did not differ between the lines. These results show that the responses to different challenges are not affected in the same way by the HPA axis activity. These results, together with production data, will allow to evaluate the relevance of this criterion of selection to increase the robustness of animals. With the financial support of the Agence Nationale de la Recherche, program ANR BIOADAPT, project SUSoSTRESS (ANR-12-ADAP-0008). Keywords: genetic selection, cortisol, stress, robustness, heat stress, weaning stress, mixing stress, pig.