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Prenatal stress can affect the offspring's behaviour, physiology, and immune parameters. This paper summarises and discusses experimental and field studies on prenatal maternal stress in pigs. Often, elevated maternal corticosteroid concentrations during gestation are used to model prenatal stress. We used prolonged oral administration of cortisol (hydrocortisone acetate, HCA) to pregnant sows, which resulted in elevated maternal plasma and salivary cortisol concentrations. This treatment induced elevated fetal basal and adrenocorticotropic hormone (ACTH)-induced plasma cortisol concentrations, as demonstrated by a pilot study. Postnatally, it reduced birth weight of the piglets, and resulted in more live born piglets and higher preweaning mortality. In addition, it reduced the female off-spring's salivary cortisol response to ACTH, and it enhanced the piglets' novelty-induced locomotion and vocalisations, and the piglets were more aggressive in a social test. Some of these effects depended on the period of gestation during which maternal cortisol concentrations were elevated, and on the sex of the offspring. These results demonstrate that piglet physiology and behaviour can indeed be affected when the mother has elevated cortisol concentrations during gestation. Regular mixing of pregnant sows with unfamiliar sows during the last third of gestation did not affect maternal salivary cortisol concentrations. Also, it did not affect the piglets' performance, behaviour, adrenocortical response to ACTH, or wound healing. Regular mixing of pregnant sows during the last third of gestation did not affect the piglets' characteristics as studied in these experiments. However, performance and behaviour of piglets were highly influenced by the social rank of their mother during gestation. Our studies have demonstrated that piglets can be affected by elevated maternal cortisol concentrations during fetal development and by social rank of the pregnant sow during gestation.