144 Nutritional advances in fetal and neonatal development: stage of gestation and placental nutrient supply

Abstract

Abstract Placental and fetal development is especially sensitive to direct and indirect effects of the maternal environment. The duration and timing of environmental insults or stimuli in relation to the stage of gestation influences the phenotypic outcomes of offspring. Nutrient restriction during early gestation, such as developing heifers on low-input forage-based management schemes followed by nutrient re-alimentation at pregnancy confirmation, increased late-term uterine artery blood flow relative to maternal body weight compared with conventionally developed heifers. In this study, calf birth weights were not different between low-input vs conventionally developed heifers, which may indicate a compensatory mechanism to safeguard late-term fetal growth. In comparison, nutrient restriction during early to mid-gestation (from day 50 to 180 of pregnancy) decreased uterine artery blood flow, decreased fetal weight, and increased placental blood vessel density in both Brahman and Angus heifers. Moreover, the efficiency of uterine artery blood flow relative to fetal weight was improved in nutrient restricted dams versus adequate fed as well as Brahman vs Angus. These responses indicate improved placental nutrient supply following early to mid-gestation nutrient restriction. Apart from nutritional management, season and melatonin supplementation impacts placental nutrient supply in cattle. Specifically, spring calving heifers with increased uterine artery blood flow had heavier calves at birth compared with their fall calving counterparts. Although several seasonal environmental changes can influence performance and reproductive traits, specific changes in hormone concentrations as a result of photoperiod may alter blood distribution to the reproductive tract. This is apparent when supplementing dairy heifers and beef cows with melatonin during the last third of pregnancy, which increased uterine artery blood flow and calf weaning weights compared with non-supplemented controls. Elucidating the consequences of specific supplements on the continual plasticity of placental nutrient supply will allow us to determine important mediators of fetal growth and development.