Uterine and umbilical blood flows and net nutrient uptake by fetuses and uteroplacental tissues of cows gravid with either single or twin fetuses.

To evaluate the influence of cow breed and number of fetuses on uterine and umbilical blood flows and nutrient fluxes or uterine tissues from gravid cows, surgery was performed on Charolais or Hereford cows with single or twin fetuses at 177 +/- .2 d (mean +/- SEM) after mating. Indwelling catheters were placed in a fetal femoral artery and vein, in an umbilical vein of each fetus, and in a uterine artery and vein of each gravid horn. Deuterium oxide (D2O) was infused into a fetal femoral vein at 183 +/- .3 and 190 +/- .5 d after mating to estimate uterine and umbilical blood flows (liters/minute). Blood oxygen and plasma glucose and lactate concentrations were determined and uterine arterio-venous (A-V) and umbilical venous-fetal arterial (v-a) differences and net uterine and fetal uptakes were calculated. Net utilization by the uteroplacenta was calculated as the difference between uterine and fetal net uptakes. Uterine blood flows were lower (P less than .01) in Hereford (4.80 +/- .28) than in Charolais (7.07 +/- .33) and lower (P less than .01) per fetus in cows with twin fetuses (5.22 +/- .34) than in cows with a single (6.65 +/- .28) fetus. Umbilical blood flows were greater for single than for twin fetuses. Fetal oxygen and glucose net uptakes averaged 57 and 12%, respectively, of net uteroplacental utilization. Lactate was released from uteroplacental tissues to fetal (42%) and maternal circulations (58%). Fetal oxygen uptakes tended to be less for twin fetuses (P = .08) than for a single fetus.(ABSTRACT TRUNCATED AT 250 WORDS)