Effects of prenatal stress on behaviour of offspring of laboratory and farmed mammals

Abstract

This article is a review of research on effects of stress experienced by pregnant females on the sex-ratio, behaviour and reproductive success of their offspring. Implications of such effects for the behaviour and welfare of farm, zoo, and pet animals are discussed. Evidence mainly from studies of rodents and primates strongly indicates that prenatal stress can impair stress-coping ability, and is able to cause a disruption of behaviour in aversive or conflict-inducing situations in juvenile and adult offspring. In non-challenging situations, however, behavioural effects of prenatal stress are frequently not seen. Prenatally stressed animals are reported to show retarded motor development, reduced exploratory and play behaviour, and impairments of learning ability, social behaviour, and sexual and maternal behaviour. Prenatal stress may affect the sex-ratio at birth, and the reproductive success of these offspring in the first, and sometimes also in the second, generation. Individual variation in the susceptibility to prenatal stress may exist. Behavioural inhibition and anxiety when exposed to novelty are typical results which may underlie the effects of prenatal stress on learning and various behavioural responses. This seems to be related to increased or prolonged activity in the hypothalamic–pituitary–adrenal (HPA) axis produced by impaired negative feedback of glucocorticoids in the hippocampus, although other neuroendocrine pathways may be involved. Effects of prenatal stress may reflect evolutionarily adaptive mechanisms, favouring production of the sex which may serve as a helper-at-the-nest (usually females) and producing an increased HPA-axis dominance in these offspring which would favour defensive behavioural reactions in competitive or stressful situations. Since behavioural and neuroendocrine effects of prenatal stress in rodents are quite similar to those found in depressed humans, and since increased fearfulness and frustration is implicated, farm animals subjected to prenatal stress may be predicted to show a reduced ability to cope with a difficult environment and also have increased propensity for developing behavioural disturbances and reduced welfare. Recent results on farmed foxes, and indications in other farm species, show that prenatal stress may affect the behavioural development of farm animals. As knowledge in this area is scarce, more research is warranted. Effects of qualitative and quantitative aspects of handling, social relations and its disruption, and environmental conditions prior to mating and during gestation could be investigated. Effects should be sought on sexual maturation, sexual behaviour, maternal behaviour, fearfulness, behavioural responses to stress and novel stimuli, and behavioural effects of frustration. The interrelation between effects on offspring of necessary stressful treatment of pregnant mothers and effects of habituation to such treatment could also be studied.