Proceedings of The Physiological Society
University of Edinburgh (2007) Proc Physiol Soc 6, C5
Pre-natal stress in the pig: effects on the behavioural and neurophysiological development of piglets
S. Jarvis1, C. Moinard1, S. K. Robson1, E. Baxter1, E. Ormandy1, A. J. Douglas2, J. R. Seckl2, J. A. Russell2, A. B. Lawrence1
1. SLS, Scottish Agricultural College, Penicuik, United Kingdom. 2. College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, United Kingdom.
Evidence in humans indicates that experiences throughout the pre-natal period affect long-term development. Babies born at term with a low birthweight are more likely to develop conditions such as diabetes type 2, hypertension and depression in adulthood. The aim of this study was to investigate the effect of pre-natal stress (social mixing) on the behavioural and neurophysiological development of piglets. Thirty-six primiparous sows were divided into two control (C) groups, two groups that were mixed during the second (Mix2) and two groups that were mixed during the third (Mix3) trimester of pregnancy. In the sows, mixing increased lesion scores (2nd trimester means (s.e.): C = 1.6 (0.1), Mix2 = 2.9 (0.3), Mix3= 1.8 (0.1) F=10.4 (anova), p=0.05. 3rd trimester means (s.e.): C=1.8 (0.1), Mix2= 1.6 (0.1), Mix3= 3.2 (0.1), F=22.7 (anova), p=0.02) and change in salivary cortisol levels (2nd trimester means (ng/ml) (s.e.): C = 0.09 (0.07), Mix2 = 2.40 (0.71), Mix3= -0.05 (0.20), F=22.3 (anova), p=0.02. 3rd trimester means (s.e.): C=0.36 (0.15), Mix2= 0.43 (0.32), Mix3= 3.47 (0.58), F=12.0, p=0.04); birthweight of their piglets was unaffected. At 60 days of age, 48 daughters were selected from the three treatments and half were challenged using a restraint test. All were culled and brain tissue collected and analysed using in situ hybridisation. We found increased CRH mRNA expression in the PVN of unrestrained Mix2 daughters (Mean CRH Cell count x grain density (se) in unrestrained piglets: C = 9.1 (3.6), Mix2= 37.3 (9.4), Mix3= 17.9 (4.5), W=6.5, p=0.04), and in the amygdala of Mix2 and Mix3 daughters (Mean CRH Cell count x grain density (se) in unrestrained piglets: C = 13.9 (2.8), Mix2= 20.7 (3.1), Mix3= 24.0 (4.4), and in restrained piglets C = 20.2 (3.7), Mix2= 33.9 (4.7), Mix3= 31.0 (5.9), W=7.6, p=0.02). At 67 days of age, 24 further daughters (8 from each treatment) were mixed, and Mix2 and Mix3 daughters showed a greater and longer salivary cortisol response than controls. At parturition Mix2 and Mix3 daughters were more restless and more responsive to piglets that approached the head of the sow, and Mix2 daughters tended to bite at their piglets more (Mean bites/hour (se): C= 0.2 (0.1), Mix2= 2.1 (0.7), Mix3= 0.1 (0.1), F=7.0, p=0.07), traits which are a component of poor maternal behaviour. Overall the results indicate that stress experienced by the mother during pregnancy can affect the behavioural and neurophysiological development of piglets resulting in more stress-reactive offspring. The effects appear to be strongest when the pre-natal stressor is applied during the second trimester of pregnancy which coincides with the development of the pig foetal HPA axis. The effects of the pre-natal stress on the maternal behaviour of the daughters could have implications for transmission of altered stress reactivity across generations.
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