Prenatal development as a predisposing factor for perinatal losses in pigs.

The pig industry is confronted with substantial losses due to piglet mortality. With 3-8% stillbirths and generally > 10% preweaning mortality, approximately one fifth of all fetuses formed fully at the end of gestation die before weaning. Most of these losses occur in the perinatal period. Overall prenatal development (birth weight) and specific prenatal developmental and maturational processes in late gestation are predisposing factors for perinatal losses. Birth weight and variation in birth weight remain important risk factors for perinatal mortality. Genetic selection against piglet mortality will not necessarily increase birth weight but will affect body composition and proportional organ development. Many maturational processes that occur in late gestation in preparation for extrauterine life, for example specific biochemical changes in the gastrointestinal tract, are influenced by glucocorticosteroids and are, therefore, dependent on maturation of the pituitary-adrenal system. The carbohydrate metabolism of perinatal piglets is related closely to viability in the perinatal period. The prenatal deposition of carbohydrate reserves (glycogen) and prenatal effects on perinatal glucogenic capacity, glucose homeostasis, carbohydrate metabolism and thermostability are reviewed.