246 Maternal resilience to gestational social stress impacts offspring cortisol response at weaning but not post-weaning growth or aggression

Abstract Exposure to social stress during gestation has been demonstrated to influence offspring health, growth, and behavior. This study aimed to characterize differences in weaned pigs previously selected from sows classified as exhibiting resilience or vulnerability to gestational social stress using salivary cortisol. In short, purebred Yorkshire litters born to first or second parity sows were selected based on the sow’s salivary cortisol pattern at an acute mixing event at 30d of gestation. Saliva was collected at 1200h each day at -1, 0, +1, +2, +3, +7d relative to social mixing. Salivary cortisol pattern was used to identify 8 females whose salivary cortisol concentrations returned to baseline as stress resilient (SR) and 8 females whose salivary cortisol concentrations remained increased as stress vulnerable (SV). We previously observed reduced average daily gain (ADG) leading to reduced weaning weight in the piglets born to SV sows. To investigate if differences exist post-weaning, we characterized the stress response to weaning, aggression at two mixing events using skin lesions as a proxy, and growth performance up to 12wk of the pigs in these 16 litters (n=85 SR, n=73 SV, n=158 total). Stress response at weaning (26 +/- 3d) was assessed by measuring serum cortisol at -2, 0, +4d surrounding weaning. Skin lesions were counted at -1, +1, +5d surrounding social mixing at weaning and again at 8wk when pigs were transitioned to grow-finish rooms. Growth performance was assessed using body weight at 8wk and 12wk, as well as ADG calculated during the nursery stage (4wk-8wk) and early grow-finish stage (8wk-12wk). Variables were treated as repeated measures and analyzed using a Gaussian linear mixed model. The base model included dam stress group, day, the interaction between stress group and day, and piglet sex as fixed effects; additionally, each model included individual animal, litter, sire, and farrowing group as random effects. Piglets born to SR sows had a greater response to weaning demonstrated by significantly higher cortisol on the day of weaning compared to piglets born to SV sows (SR: 183 +/- 22nmol/L, SV: 140 +/- 23nmol/L, P< 0.001). Piglets did not differ in cortisol concentration pre-weaning (P=0.439) or 4d post-weaning (P=0.764). At 8wk, pigs born to SR sows did not differ in body weight from those born to SV sows (P=0.843), but they tended to weigh more at 12wk (SR: 43.5 +/- 0.9kg, SV: 41.8 +/- 0.9kg, P=0.085). Pigs did not differ in ADG during the nursery or early grow-finish stages. No significant differences in skin lesions were detected at weaning or 8wk social mixing events. These results suggest that exposure to prenatal social stress and maternal resilience may alter acute stress response but not post-weaning performance.