Prenatal stress in sheep: Alteration of emotional reactivity and of cognitive functions and alleviative effect of positive emotions – Psy-sheep

This project took place over three years and was composed of three main tasks.
The first task was to select ewes that were more or less reactive to stress and submit during gestation half of the animals to a stressful treatment already validated in the team (repeated exposure to unpredictable and uncontrollable aversive events such food delay distribution, wet litter, transport, …). At lambing, the effect of prenatal stress on maternal behavior of the ewes (maternal care, maternal motivation) was studied.
The second task was to assess emotional reactivity and cognitive function of the lambs through psychological and cognitive tests. Six lambs from both groups were studied to explore the consequences of prenatal stress in brain morphology.
The third task was to rear, during the juvenile period, lambs that were prenatally stressed or not, with additional events of positive valence (positive contrasts, anticipating food distribution ...) in order to find a way to neutralize the negative effects of the prenatal stress.

The results show that a stressful experience during pregnancy and the reactivity level of the ewes partially impair the establishment of maternal behavior and had negative effects on the behaviour and the brain morphology of the lambs. It could affect their futures adaptation to their environment and their welfare. These negative effects were even greater in lambs from high reactive ewes. However, the enrichment of rearing conditions may partly counteract the negative effects of prenatal stress.

It would be interesting to study later, the long-term impact of prenatal stress and to improve the protocol of enrichment.

This project produced a scientific publication in an international journal, 8 congress communications (including 5 international conferences) and 2 Articles in popular magazines for farmers and veterinarians.

Consequences of stress are an issue of major relevance to human health, especially its negative influences on cognition and emotion. Results suggest that the younger the individual, the more harmful are the consequences of the stress. There is considerable evidence indicating that stress experienced by a mother during pregnancy can act as a predisposing risk factor in the development of behavioural and cognitive problems at adulthood involving hyperactivity and attention deficit disorder in the offspring and increased vulnerability to develop psychiatric disorders such as depression and schizophrenia. Nevertheless, it has been observed that these disorders may not develop if the adequate postnatal stimulation is given. Research on prenatal stress (defined as the stress experienced by the pregnant mother which affects the development of the offspring) has been performed in experimental animals (mostly in altricial species like in rodents). With rodents, it is possible to study the differentiation between genetic and postnatal factors, to control the timing, intensity and duration of stress exposure and evaluate the mother-offspring interactions in a controlled environment. However, a considerable amount of neuroendocrine and neural development occurs in the rodent brain after birth, making the pups more sensitive to postnatal environmental conditions and maternal attention; this can contribute to the overall effect of prenatal stress on offspring behaviour. In contrast to this context, we decided to study prenatal stress on a precocial species, the sheep, because of their brain maturity before birth and the strong bond that develop between the ewe and her lamb which is not the case in altricial mammals.
The aim of my study is to investigate the effect of prenatal stress on sheep, according to the emotional reactivity of the dams, on (1) their maternal behaviour, (2) the emotional reactivity and cognitive abilities of the young and (3) and to find possible ways to alleviate its negative consequences by the induction of positive affective experiences. In addition, the stress sensitive brain pathways associated with neural damage and neural protection will be investigated. The project is running along 3 years. Our first objective will be to select dams with extreme reactivity to stressful events in one hand and dams with very low reactivity to the other hand and to apply in both categories stressful events during the gestation. Then we will look at the maternal behaviour of the dams and how prenatal stress could interfere according to their emotional reactivity tested beforehand. Our plan is to realize cross fostering between the dams stressed during gestation and the control dams to pull apart the effects of the stress acting directly on the foetus before birth and the effects of the maternal behaviour acting on the young after birth. Emotional reactivity and judgment biases of young will be investigated. The last objective aims to subject prenatally stressed young to supposedly positive events in order to elicit positive experiences and to assess the putative therapeutic value of that behavioural strategy. In addition, the effect of prenatal stress and of positive emotion on brain morphology will be investigated in brains of the young. An originality of this project is to combine behavioural and neurological studies on the consequences of prenatal stress. This project of fundamental research will increase our knowledge on the effect of prenatal stress on emotional reactivity and cognitive abilities of individuals.