Associations between Resilience to Early-Life Stress and Behavior in Finishing Gilts

Andrea M Luttman, Bora Lee, Janice M Siegford, Nancy E Raney, Juan P Steibel, Catherine W Ernst

Weaning is an acute early-life stressor and therefore, an excellent model for examining lasting impacts of stress resilience. Our objective was to identify gilts exhibiting resilience or vulnerability to weaning stress and characterize long-term impact on behavior. At weaning, blood samples were collected from all gilt piglets of 17 crossbred litters (n=112) at -1d, 0d, and +4d pre- and post-weaning. Serum cortisol concentrations were quantified using a commercial porcine-specific ELISA kit. For each litter, serum cortisol was used to identify the gilt most capable to return to baseline concentrations by +4d as stress resilient (SR, n=17) and the gilt least capable as stress vulnerable (SV, n=17). SR and SV gilts were followed and mixed into new social cohorts at approximately 8 wk-of-age. Skin wounds counts were recorded at -1d, +1d, and +4d surrounding the mix event. At approximately 12 wk-of-age, SR and SV gilts underwent a novel object test (NOT) to assess reactivity to a novel situation. Measures collected during the NOT included latency to cross 1m line from object, latency to cross 0.5m line from object, latency to touch object, total vocalizations, and percent of vocalizations that were high pitched. A paired t-test was conducted to analyze differences between SR and SV gilts. SR gilts had significantly more skin wounds at 1d post-mixing than SV gilts (P=0.007). No significant differences in vocalizations or latency to cross 1m line from object were found between the two groups. However, SR gilts had significantly shorter latency to cross the 0.5m line (P=0.010) and marginally shorter latency to touch the novel object (P=0.088). We found behavioral differences associated with resilience to weaning stress. Gilts resilient to weaning stress engaged in more agonistic behavior at mixing and were bolder when faced with a novel situation.