Reproduction Abstracts

For ruminant livestock producers, appropriate maternal nutrition during pregnancy is central to the production of viable offspring of optimal birth weight, and impacts postnatal growth, body composition, and reproductive potential. Young still-growing adolescent mothers are particularly vulnerable to nutritional extremes and assisted conception procedures have helped define the relative importance of diverse nutritional exposures. Pre-conception nutrition (via manipulation of embryo donors) does not affect the feto-placental growth trajectory but low maternal nutrient status at conception (via manipulation of embryo recipient BMI) negatively influences placental growth and impacts lamb birth weight. However, it is gestational intake after conception which has the most profound influence on fetal development. In adolescents overnourished throughout gestation (2× optimal control (C) dietary intakes), growth and adiposity of the mother is promoted at the expense of the conceptus. Placental growth, uteroplacental blood flows and fetal nutrient supply are severely compromised and premature delivery of low birth weight lambs (30–40% smaller than C) ensues. A more modest effect on fetal growth (15–17% decrease) is evident in undernourished mothers (0.7×C intake). Here gradual depletion of maternal body reserves directly lowers nutrient availability in the maternal circulation independent of placental size and gestation length is normal. These variations in prenatal nutrient supply differentially impact the structure and function of tissues and organs central to traits of economic importance in postnatal life. Some effects are permanent and sex-specific (e.g. reduced ovarian follicle reserve), while others are transient and/or modified by subsequent nutritional exposures (e.g. hypothalamic-appetite pathways, growth-adiposity trajectories).