Our long-term goals are to characterize the life-long and intergenerational effects of early life social stress as well as prenatal social stress on resilience in the pig, and to identify molecular mechanisms underlying those effects. Resilience is a pig's capacity to cope with a stressor and rapidly return to its pre-stress state. It is a key component of robustness, where a robust pig is a pig with high production potential that is resilient to external stressors. With a growing emphasis on group housing throughout the production cycle, including group housing of gestating females, additional research into social stress is necessary.In this study, we propose using cortisol and chromogranin A (CgA) to quantify physiological stress response and recovery to classify animals as either stress resilient (SR) or stress vulnerable (SV) at a critical mixing event. A behavioral proxy for aggression, as well as behavioral measures of fearfulness, will be used to estimate impacts of stress resilience on animal welfare. We will also investigate effects of social stressors on subsequent stress response that would indicate programming of stress regulation mechanisms has occurred. Finally, to elucidate the underlying molecular mechanism that might explain associations between stress resilience and these phenotypes, we will evaluate both mRNA transcript changes, as well as epigenetic alteration in DNA methylation in biologically relevant tissues. These tissues will include peripheral blood mononuclear cells (PBMC), hypothalamus, and amygdala which all have strong links to stress regulation and fear behavior. This knowledge will facilitate development of novel strategies to select for gilts less affected by social stress during development and gestation, thereby mitigating detrimental effects of prenatal stress on economically important pig production traits. Specific aims are to:Aim 1. Characterize stress resilience in pigs at weaning and estimate effects on future stress response.We will quantify stress response at weaning using physiological and behavioral biomarkers to identify female pigs exhibiting SR or SV responses. We will also examine whether response to weaning stress predicts behavioral and physiological stress responses later in life and investigate underlying molecular differences in PBMC, hypothalamus, and amygdala.Aim 2. Identify sows exhibiting varying stress responses in group housing during gestation and investigate molecular and phenotypic differences among their offspring at parturition.We will identify sows exhibiting SR or SV response to group gestational housing using physiological and behavioral biomarkers of stress. In addition, we will analyze gene expression and DNA methylation profiles of PBMC, hypothalamus, and amygdala from neonatal female piglets of SR and SV sows.Aim 3. Characterize differences in stress response and behavior of offspring associated with prenatal social stress and elucidate underlying molecular mechanisms.We will follow female piglets of SR and SV sows through weaning and subsequent mixing to estimate the intergenerational impact of prenatal social stress on offspring stress resilience. We will also perform behavioral tests to characterize impact of prenatal social stress on offspring fear behavior, and investigate underlying molecular differences in PBMC, hypothalamus, and amygdala.