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Behavioural and physiological consequences of acute social defeat in growing gilts: effects of the social environment

By M. A. W. Ruis, J. de Groot, J. H. A. te Brake, E. D. Ekkel, J. A. van de Burgwal, J. H. F. Erkens, B. Engel, W. G. Buist, H. J. Blokhuis, J. M. Koolhaas

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Endocrine, behavioural and immunological processes, together with body growth, were evaluated in gilts that were defeated at 10 weeks of age in resident-intruder tests. Immediately after defeat, gilts were either separated from or reunited with a familiar conspecific (litter-mate; always a barrow). Gilts were assigned to one of four treatments: (a) DI: defeat, followed by isolation (separation from original litter-mate; n=8); (b) I: no defeat, isolation (control group; n=9); (c) DP; defeat, followed by pair-housing (reunion with original litter-mate; n=8); and (d) P: no defeat, pair-housing (control group; n=8). The following general conclusions were derived: (1) social defeat caused pronounced short-term elevations in hypothalamic-pituitary-adrenal (HPA) and sympathetic-adrenal medullary activities, and of prolactin levels. Moreover, as soon as 1 h after defeat, percentages of blood lymphocytes and neutrophilic granulocytes were, respectively, decreased and increased; (2) social defeat had some long-lasting influence on behaviour and physiology, but isolation predominantly determined responses in the longer term. Defeat, as well as isolation, resulted in increased cardiovascular activities compared to P controls, as observed in a novel object test (NOT: +7 days) and an aversion test (AVT: +14 days). Moreover, defeated as well as isolated gilts did not habituate to a repeated novel environment test (NET: -7, +2 and +7 days) in terms of frequencies of vocalising, whereas P controls did. Isolation, through the separation from any other pig, was responsible for the other observed long-term characteristics, which developed progressively. Isolated gilts showed high mobilities and high cortisol responses in the repeated NET (+7 days), not being habituated. This contrasted the reactions of pair-housed gilts, which were much reduced. In addition to their high cardiovascular activities in the NOT and the AVT, isolated gilts also displayed higher heart rates in the repeated NET and during human presence following the NOT, compared to pair-housed gilts. Finally, isolated gilts were more inhibited to approach a novel object (in the NOT) than pair-housed pigs; and (3) stress responses of defeated gilts were modulated by the subsequent social environment. Stimulation of the HPA-axis (plasma- and salivary cortisol) was prolonged in those defeated gilts which were isolated (observed in the first hour). Changes in leucocyte subsets were still observed after 3 days in DI, but were 'normalised' within 1 day in DP gilts. Two days after defeat, habituation to the repeated NET in terms of mobility and salivary cortisol responses occurred in control and DP gilts, but not in DI gilts. We argue that these effects of the social environment shortly after defeat were related to a stress-reducing effect of a stable social relationship, i.e. social support.

Date 2001
Publication Title Applied Animal Behaviour Science
Volume 70
Issue 3
Pages 201-225
ISBN/ISSN 0168-1591
DOI 10.1016/S0168-1591(00)00150-7
Language English
Author Address Department of Behaviour, Stress Physiology and Management, Institute for Animal Science and Health, P.O. Box 65, 8200 AB Lelystad, Netherlands.
Cite this work

Researchers should cite this work as follows:

  1. Animal behavior
  2. Animal husbandry
  3. Animal immunology
  4. Animal physiology
  5. Behavior and behavior mechanisms
  6. Cortisol
  7. Gilts
  8. Hydrocortisone
  9. Immunity
  10. Isolation
  11. Mammals
  12. peer-reviewed
  13. physiology
  14. piggeries
  15. pig housing
  16. Pigs
  17. saliva
  18. Social Environments
  19. social situation
  20. sties
  21. Stress
  22. Swine
  1. peer-reviewed