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1. Blood gas tensions, pH, PCV, O₂ 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 O₂ affinity. In six animals the mean P₅₀ of the foetal blood (24·8 mmHg) was considerably lower than that of the mother (35·5 mmHg); no changes in P₅₀ 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 O₂ and the differences in P₅₀ between foetus and mother could be ascribed to the presence of a foetal haemoglobin.

4. In the sow large differences in O₂ affinity between foetal and maternal blood were observed, which were related to red cell 2,3-DPG concentration. A rise in foetal blood P₅₀ 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 P₅₀ 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 O₂ 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_O2 gradients and the O₂ requirements of the foetus and neonate.

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				J. L. Vallet and B. A. Freking Differences in placental structure during gestation associated with large and small pig fetuses J Anim Sci, December 1, 2007; 85(12): 3267 - 3275. [Abstract] [Full Text] [PDF]