Altered adrenocortical response to acute stressors or ACTH(1-24) in intensively housed pigs

In two experiments, the effect of intensive housing on behavior and adrenocortical reactivity was studied in 68 castrated male German Landrace pigs. In both experiments, half of the pigs were tethered on a partially slatted floor without straw and half were kept, as controls, in groups on straw. Prior to the study, 32 of the pigs used in the first experiment were selected according to their reaction to halothane anesthesia; for the second experiment, 36 pigs were selected according to their adrenocortical response to azaperone-metomidate anesthesia. During the 4- to 6-wk experimental period, behavioral activity was observed and adrenocortical reactivity was analyzed after stimulation with synthetic ACTH(1-24), azaperone-metomidate anesthesia, insulin-induced hypoglycemia and neostigmine-atropine. Although no difference was found in general activity between groups, tethered pigs revealed a significantly higher cortisol increase after stimulation with ACTH(1-24) in both experiments and after insulin stimulation in the second experiment. Similarly, the area below the cortisol response curve after ACTH stimulation was significantly larger in tethered pigs in the second experiment. The individual reaction pattern was positively correlated between tests, indicating this pattern is a relatively constant, individual characteristic. In contrast, no correlation was found between behavior or adrenocortical reaction pattern and sensitivity to halothane. The results suggest that tethering on a partially slatted floor constitutes a chronic stressor which changes the adrenocortical response to an additional acute stressor. This increased reactivity is revealed most clearly after stimulation with ACTH(1-24) when individual responsiveness is taken into consideration.