Prenatal stress affects anxiety-related behavior and the well-being of sows

Sows that experience prenatal stress are more anxious as adults, and when they become mothers themselves, they are less maternal toward their offspring. This finding has implications for animal welfare and may explain the wide variation in maternal behavior in pigs.   The stress experienced by piglets during gestation predicts the level of stress they will experience after birth. This ancient transmission mechanism, shared by all vertebrates, allows animals to adapt to a challenging environment. However, this prenatal stress can have significant consequences for animal health and animal welfare, particularly by causing morphological, behavioral, and physiological changes. Maternal stress is an important marker of the environmental conditions in which animals live. Given its direct impact on animal welfare in livestock production and the importance of the swine model in translational research, researchers at the Roslin Institute and Scotland’s Rural College set out to study its effects in domestic pigs. Pregnant primiparous sows were exposed, midway through their gestation, to a social stressor (mixing with unfamiliar conspecifics). This study reveals that prenatal stress affects the brain cells that regulate anxiety-related behavior. It alters corticotropin-releasing hormone receptors exclusively in female piglets. At 10 weeks of age, their mRNA levels—which encode corticotropin-releasing hormone (CRH), measured here for the first time in pigs—were higher in the amygdala. Released in response to stress, this molecule indicates a neurobiological predisposition to anxious behavior. When monitored over the long term, sows that experienced prenatal stress subsequently exhibit negative maternal behavior at the birth of their first piglets, regardless of their environment. They spend more time lying on their stomachs or standing, and change positions more frequently. They are also more responsive to their piglets’ cues and spend more time visually observing them. This abnormal maternal care is further associated with a higher mortality rate among piglets raised in an open pen, where they are less protected. Prenatal stress in pigs can therefore negatively shape the brain development of females and lead to a pro-anxiogenic phenotype. These changes not only impair their well-being but also result in deficient maternal behavior later on. These findings have important implications for animal welfare, as animals are most often kept in captivity in an artificial environment. They also shed new light on the role of pigs as a relevant animal model for studying the effects of prenatal stress.