Causes and consequences of fetal growth retardation in pigs.

In pigs, as in other species, fetal growth retardation is associated with reduced birth weight and increased risk of fetal and neonatal death. As there are few opportunities after birth to remedy the detrimental effects of low birth weight, it is important to understand both the intrinsic and extrinsic factors associated with inadequate fetal growth and to determine when growth retarded fetuses deviate from the growth trajectory of their normal sized littermates. Inadequately grown pig fetuses can be identified statistically as early as day 30 of the 114 days of gestation, indicating that limited uterine space is not a primary determinant of fetal growth. Comparisons of the smallest fetus within a litter with a normal sized sibling reveal that inadequately grown fetuses have altered endocrine status and lower circulating concentrations of many essential amino acids. In addition, the placenta supplying the smallest fetus is disproportionately small and has a reduced capacity to transport amino acids. Understanding the timing and the causes of fetal growth retardation in pigs may help us to devise appropriate strategies to reduce the incidence and hence the detrimental postnatal consequences of runting.