Relation between Metabolic Rate and Body Size in the Ovine Fetus

Abstract

Objectives were to describe the relations between fetal oxygen consumption (V̇O2), vital organ weights and body weight in sheep during growth between mid gestation and term (about 147 d). Umbilical V̇O2 in conscious, single-pregnant ewes and fetal wet and dry body weights were measured at 73–97 d (n = 14) and at 119–141 d (n = 28) of gestation. Fetal wet and dry organ weights were related to body weights in an additional seven single-pregnant and eight twin-pregnant ewes at 73–140 d. Fetal V̇O2/kg wet weight decreased by 25% between mid and late gestation, whereas V̇O2/kg dry weight decreased by 56% and was paralleled by a similar decline in the relative aggregate weight of the vital organs (liver, kidneys, heart, brain). Log-log regression of V̇O2 on dry body weight, and of dry vital organ weight on dry body weight yielded coefficients of 0.73 ± 0.02 and 0.66 ± 0.01, respectively, suggesting that a decline in the relative growth of metabolically active organs explains much of the decline in weight-specific V̇O2 during fetal development.