title: The hypothalamo-pituitary-adrenal (HPA) axis in sheep is attenuated during lactation in response to psychosocial and predator stress.
abstract: Activation of the hypothalamo-pituitary-adrenal (HPA) axis by psychosocial stress is attenuated during lactation. We tested the hypothesis that lactating ewes will have attenuated HPA axis responses to isolation and restraint but will have greater responses to predator stress in the form of barking dogs. We imposed two 4 h stressors: psychosocial stress (isolation and restraint of ewes) and predator stress (barking dogs). Blood was collected intravenous every 10 min from nonlactating ewes (n = 6), lactating ewes with lambs present but not able to be suckled (n = 6), and lactating ewes with lambs present and able to be suckled (n = 6). Plasma cortisol and oxytocin were measured. For nonlactating ewes, cortisol increased (P < 0.01) in response to both stressors, and these increases were greater (P < 0.01) than that in the lactating animals. For lactating ewes with lambs present but unable to be suckled, cortisol increased (P < 0.05) in response to both stressors with a greater response to barking dogs (P < 0.05). For lactating ewes with lambs present and able to be suckled, cortisol increased (P < 0.01) in response to barking dogs only. Plasma oxytocin was greater (P < 0.01) in lactating ewes than in nonlactating ewes and did not change in response to the stressors. In conclusion, lactating ewes are likely to have a greater HPA axis response to a stressor that may be perceived to threaten the welfare of themselves and/or their offspring. The role of oxytocin in attenuation of the HPA axis to stress in sheep is unclear from the current research and requires further investigation.
authors.affiliation: Division of Livestock and Farming Systems, South Australian Research and Development Institute, The University of Adelaide, Roseworthy, South Australia, 5371, Australia. Electronic address: cameron.ralph@sa.gov.au.
authors.forename: C R
authors.initials: CR
authors.lastname: Ralph
authors.affiliation: Department of Physiology, Monash University, Melbourne, Victoria, 3800, Australia.
authors.forename: A J
authors.initials: AJ
authors.lastname: Tilbrook
mesh_terms: D000818:Animals; D000833:Animals, Suckling; D004285:Dogs; D005260:Female; D006854:Hydrocortisone / Q000097:blood / Q000378:metabolism; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology*; D007774:Lactation / Q000502:physiology*; D010121:Oxytocin / Q000378:metabolism; D010913:Pituitary-Adrenal System / Q000502:physiology*; D011235:Predatory Behavior; D012149:Restraint, Physical; D012756:Sheep / Q000502:physiology*; D013312:Stress, Physiological / Q000502:physiology*; D013315:Stress, Psychological; D014828:Vocalization, Animal
chemical_list: D010121:Oxytocin; D006854:Hydrocortisone
keywords: HPA axis; Hyporesponsiveness; Lactation; Oxytocin; Stress