Birth weight, dystocia, and neonatal survival

Neonatal adaptation

Neonatal immune function

Summary

References

INTRODUCTION

The greatest loss in ruminant production systems occurs during the neonatal period, that is, between birth and 28 days of life. In extensive production systems, neonatal losses are reportedly between 10% and 30% and 6% and 16% for lambs and calves, respectively. With 90% of these offspring born alive, this is considered a preventable welfare issue1 and a high economic burden to the livestock industry. It is well established that in utero environment3 affects ruminant progeny health and welfare. This phenomenon is known as fetal programming and is contingent upon the particularly long gestation period in ruminants during which physiologic systems develop, such that at birth, the ontogeny of these systems is complete. The effects of this fetal programming in the neonate may be mediated by epigenetic modifications that regulate gene expression in both the placenta and the fetus (Fig. 1). These epigenetic modifications may occur as early as embryogenesis through to late gestation. The placenta mediates fetal supply of nutrients, hormones, and oxygen with both the placenta and the fetus responding to maternal perturbations in a sexually dimorphic manner. This dimorphism has significant consequences because survival in the male fetus, during gestation and at birth, is reduced compared with the female fetus. Significantly for this review, many of the contributing factors associated with increased risk of neonatal mortality, that is, premature birth, birth weight, dystocia, and poor adaptation to the postnatal environment, are consequent to the prevailing prenatal environment.