Behavior and pituitary-adrenal function in Large White and Meishan pigs

Six-wk-old piglets of both sexes from European Large White (LW, n = 36) and Chinese Meishan (MS, n = 24) breeds were individually exposed to a novel e nvironment, a stressful stimulation. Behavioral and pituitary-adrenal react ivity were investigated. When compared with LW, MS pigs displayed low locom otion (18.5 +/- 2.2 vs. 41.0 +/- 3.8 squares crossed/10 min; P < 0.0001), a nd defecation scores (0.58 +/- 0.15 vs. 4.86 +/- 0.37 fecal boli; P < 0.000 1). Basal concentrations of cortisol were higher in MS (96.1 +/- 1.1 vs. 44 .9 +/- 1.1 ng/ml; P < 0.0001), although no differences between breeds were found in basal concentrations of adrenocorticotropic hormone (ACTH). In res ponse to novel environment exposure, the ACTH increase was greater in LW th an in MS, but the cortisol response was not different on a log scale. To fu rther investigate the pituitary-adrenal differences between the two breeds, the 24-hr profile of ACTH and cortisol plasma concentrations, a corticotro pin-releasing factor (CRF) and a coupled dexamethasone-ACTH test were studi ed. Five castrated male 9-wk-old piglets from each breed were fitted surgic ally with a jugular vein catheter. A classic marked circadian rhythm of cor tisol and a weak nycthemeral variation of ACTH were found. Cortisol concent rations were approximately twice higher in MS exclusively during the early light phase (from 0800-1200 hr) of the cycle, but no significant interbreed difference was found in the circadian rhythm of ACTH. Administration of CR F (1 mu g/kg iv) induced the same significant increase in plasma ACTH and c ortisol concentrations in both breeds. Administration of ACTH (10 mu g/kg i v) increased significantly cortisol concentrations and revealed no differen ce in plasma cortisol response to ACTH. These data suggest that the hyperco rtisolism of MS pigs is of adrenal origin, and related to extrapituitary fa ctors that control the adrenal sensitivity during the light phase of the di urnal cycle. (C) Elsevier Science Inc. 1999.