|RAULT, JEAN-LOUP - Purdue University|
|CARTER, C - University Of Illinois|
|GARNER, JOSEPH - Purdue University|
|RICHERT, BRIAN - Purdue University|
|Lay Jr, Donald|
Submitted to: Physiology & Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2013
Publication Date: 3/15/2013
Citation: Rault, J., Carter, C.S., Garner, J.P., Marchant Forde, J.N., Richert, B.T., Lay Jr., D.C. 2013. Repeated intranasal oxytocin administration in early life dysregulates the HPA axis and alters social behavior. Physiology and Behavior. 112-113:40-48.
Interpretive Summary: Pigs and other farm animals typically experience several regroupings depending on their production stages, which can result in social stress. These situations can involve aggression and social stress which leads to detrimental effects on swine health and productivity. In contrast to aggressive interactions, positive social interactions can reduce the adverse effects of social stress. These beneficial effects derived from positive interactions may be mediated by oxytocin, a neuropeptide underlying social behavior. Social behavior is a major concern for farm animal welfare. To date, no study has investigated the role of OT in the social behavior and stress coping abilities of farm animals. To investigate this, in each of six litters, two pigs per litter received oxytocin intranasally and two control littermates received saline at 1, 2 and 3 days of age. Pigs were weaned at 17 days of age and mixed individually with four unfamiliar pigs. This social mixing was repeated at 8 weeks of age. On each occasion, we analyzed behavior, and collected blood samples to measure stress hormones. Oxytocin administered pigs were involved in more aggression when mixed and showed a greater stress response after weaning at 17 days of age, with a few effects persisting at mixing at 8 weeks of age. Overall, this study confirmed that pigs repeatedly administered oxytocin after birth show behavioral and physiological differences compared to non-treated pigs. However, these modifications could be detrimental as oxytocin treated pigs showed increased aggression and a long-term dysregulation of their stress response. A better knowledge of the neurobiological mechanisms of social behavior will help to clarify how different husbandry practices can lead to various outcomes in animal health and well-being.
Technical Abstract: Aggression and social stress are major welfare concerns when regrouping captive animals, with detrimental effects on health. In contrast, positive social interactions can reduce the adverse effects of social stress in humans and other animal species. This reduction may be mediated by oxytocin (OT), a neuropeptide underlying social behavior. Oxytocin is able to buffer the hypothalamo-pituitary-adrenal (HPA) axis. We hypothesized that repeated postnatal OT administration to neonatal pigs could provide long-lasting protective effects against social stress. In each of six litters, two pigs per litter received 0.25 mL (24 IU or 50 µg) of OT intranasally and two control littermates received 0.25 mL of saline as a control, at 1, 2 and 3 days of age. Pigs were weaned at 17 days of age and mixed individually with four unfamiliar pigs. This social mixing was repeated at 8 weeks of age. On each occasion, we analyzed behavior over 4 h after mixing and collected blood samples to analyze cortisol and adrenocorticotropic hormone (ACTH) over 2 days after mixing. The pigs were then submitted twice to a resident-intruder test at 9 weeks of age, and to a dexamethasone suppression test and corticotropic releasing hormone administration (Dex-CRH) challenge at 11 weeks of age. After weaning, OT-administered pigs received more aggressive interactions (P = 0.03), performed more parallel and head push behaviors in return (P = 0.04 and P = 0.04 respectively), showed greater locomotion (P = 0.03), and spent less time lying next to penmates (P = 0.04) than control pigs. The OT pigs also had greater cortisol concentrations 24 h before and 24 h after weaning (P = 0.05 and P = 0.05 respectively) and tended to have greater ACTH concentrations 24 h after weaning (P = 0.09). After mixing at 8 wk of age, OT pigs still tended to perform more head push behavior than control pigs (P = 0.06) and had greater ACTH concentrations 24 h after mixing (P = 0.004). The Dex-CRH challenge revealed that OT pigs were less responsive to dexamethasone than control pigs (P = 0.01), traducing a deficient HPA axis’ negative feedback control. Postnatal OT administration altered social behavior and resulted in a long-term dysregulation of the HPA axis, at least until 11 weeks of age. This study brings new knowledge regarding the neurobiological mechanisms of swine social behavior and stress-coping abilities, along with possible implications for the clinical use of OT for autistic children given the dysregulation of the HPA axis and possibly similar social deficits.