A comparative study of blood gas tensions, oxygen affinity and red cell 2,3 DPG concentrations in foetal and maternal blood in the mare, cow and sow.

1. Blood gas tensions, pH, PCV, O(2) affinity and red cell 2,3-diphosphoglycerate (DPG) levels have been measured in uterine and umbilical blood in conscious cows and mares with indwelling vascular catheters and in sows under sodium pentobarbitone anaesthesia.2. Large P(O2) gradients (20-24 mmHg) were observed between the uterine and umbilical venous blood in the cow and pig, while in the mare the corresponding P(O2) difference was only 2.7 +/- 1.7 mmHg. Alterations in maternal arterial P(O2) did not affect the large vein-to-vein P(O2) difference in either ruminant or pig.3. In the cow the presence of different haemoglobin types in the adult (A, AB or B) did not appear to affect the O(2) affinity. In six animals the mean P(50) of the foetal blood (24.8 mmHg) was considerably lower than that of the mother (35.5 mmHg); no changes in P(50) were observed during the last month of gestation. Red cell 2,3-DPG levels were higher in the calf foetus than in the mother, but in the ruminant 2,3-DPG has no effect on the affinity of haemoglobin for O(2) and the differences in P(50) between foetus and mother could be ascribed to the presence of a foetal haemoglobin.4. In the sow large differences in O(2) affinity between foetal and maternal blood were observed, which were related to red cell 2,3-DPG concentration. A rise in foetal blood P(50) during the last half of gestation was associated with increased foetal weight and a rise in red cell 2,3-DPG.5. In the mare the P(50) of the foetal blood was 2-5 mmHg below that of the mother. This difference appeared to be due to the lower 2,3-DPG concentration in the foetal red cells as in the sow; in both species the haemoglobin of the foetus is similar to that of the mother.6. The differences in foetal and maternal O(2) affinity found in the various species and the changes which may occur during gestation or in the perinatal period are discussed in relation to the observed transplacental P(O) (2) gradients and the O(2) requirements of the foetus and neonate.