Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 11, 1997
Publication Date: N/A
Interpretive Summary: Understanding the physiology of pregnancy and fetal development will lead to strategies aimed at improving reproductive traits, and ultimately increases in litter size in swine. The objective of this research was to gain insight on the cause of fetal death by studying the development of the blood supply and liver in the swine fetus during a period of gestation that tis critical for fetal survival in a crowded uterine environment. Using prolific Chinese Meishan gilts and a model of uterine crowding in domestic white crossbred gilts, we compared the development of red blood cells and other traits in developing pig fetuses from day 24 to day 40 of gestation (term=114 days). Our results show that the Meishan pig may have an advantage in the amount of placenta supplying each fetus as well as a faster developing blood supply, despite slower fetal growth than the domestic pig. These results suggest that the physiology of pregnancy has been altered in the Meishan pig, bred primarily for litter size, to increase fetal survival. Also, pigs in a crowded uterine environment showed lower fetal survival and an altered relationship between fetal weight and blood hemoglobin or packed red blood cell volume at d40. These results suggest that the fetuses in a crowded uterine environment may be compromised in their capacity to generate sufficient blood for survival. Understanding the mechanisms behind these observations may lead to strategies for stimulating the development of the blood supply of the fetus during pregnancy, increasing the chance that more fetuses will survive to term.
Technical Abstract: This study investigated erythropoiesis and fetal liver protein secretion on d24, d30 and d40 of gestation in pigs from domestic white crossbred (WC) gilts with a normal (intact; INT) or crowded (unilateral hysterectomized/ ovariectomized; UHO) uterine environment or prolific Chinese Meishan (MS) gilts. Increased total red blood cells (RBC), hematocrit, blood hemoglobin content, and maternal plasma erythropoietin (EPO) levels were observed as gestation advanced. Cultured fetal liver secretion of transferrin (TF) and a protein of Mr 12,500 and pI 7.5 also increased. Fetal plasma EPO declined between d30 and d40. Counts of circulating erythroid precursors revealed a decline in basophilic polychromatic erythroblasts (BE and PE) between d24 and d40, an increase in orthochromatic erythroblasts (OE) on d30 followed by a drop on d40, and an increase in reticulocytes/erythrocytes from <1.0% to approximately 90% of circulating RBC between d24 and d40. Differences among groups included a lower fetal survival percentage in UHO (vs. INT or MS) on d40, and greater maternal hematocrits, fetal weights, fetal hematocrits, fetal EPO levels and liver TF secretion in WC vs. MS pigs. Meishan pigs had a lower percentage of PE overall and a higher percentage of OE on d24 followed by a higher percentage of erythrocytes on d40 than WC pigs, suggesting a more mature erythron in the MS. Covariate analysis indicated that the MS has relatively larger placentas than WC. Conclusions were: 1) d24-40 of gestation is a critical time period for fetal erythropoiesis, 2) the MS breed may differ in the development of the erythron, and 3) the UHO procedure did not significantly affect erythropoiesis, but did alter fetal survival and the relationship between fetal weight and both hematocrit and hemoglobin on d40.