The use of dexamethasone to attenuate stress responses of post-weaned pigs exposed to a mixing challenge

Weaning piglets usually involves mixing of non-littermate pigs into a new environment that causes social and physical stress due to the vigorous fighting and contributes to the post-weaning growth check. Dexamethasone (DEX) is a synthetic corticosteroid shown to attenuate stress responses via negative feedback on the hypothalamic-pituitary-adrenal (HPA) axis. The hypothesis tested in this study was that DEX given before the imposition of a stressful challenge, namely mixing non-littermate pigs, would ameliorate the stress response, sustain gastrointestinal tract (GIT) function, and increase growth performance. At weaning (d0), 96 male piglets (6.5 ± 0.9 kg) were allocated into pens with their littermates (4/pen) and allowed to acclimate for 14 days, at which point they were allocated to a 2 × 2 factorial arrangement of treatments from d14 to d28 with the respective factors being (i) treatment (administration of DEX or saline; DEX v SAL) and (ii) group type (mixing of non-littermate pigs or pigs kept as littermates; MIXED v NonMIXED). The study finished on d28 after weaning. On d12 and 13, pigs in the DEX treatment were given intramuscular injections of 0.2 mg/kg DEX at 0600 h and 1800 h (total 4 doses/pig; 0.8 mg/kg), while pigs in the control treatment were given the same volume of SAL. On d14 at 0800 h, 48 pigs were mixed with non-littermates and 48 pigs remained with their littermates. Individual body weights were measured weekly, and blood was collected at 1200 h on d11, d14 (4 h after mixing), and d16. On d14 and 16, four pigs per treatment group (n = 16) were given an intra-gastric dose of a solution containing 2.5 mL/kg 20% mannitol and 0.036 g/kg Co-EDTA to test gastrointestinal permeability. Plasma cortisol was greater (P = 0.001) in MIXED pigs at both 4 h after mixing (d14) and 2d after mixing (d16). Pigs given DEX tended (P = 0.100) to have a reduced cortisol concentration at day 14 regardless of the mixing treatment. The concentration of d-mannitol in plasma was reduced (P = 0.024) in pigs dosed with DEX compared to control pigs two days after mixing (d16). Growth performance was not improved by DEX treatment during the study. These results suggest that DEX has the ability to reduce some plasma stress markers and reduced intestinal permeability, possibly due to its anti-inflammatory properties, although DEX treatment did not improve performance