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Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/2/2015 Publication Date: 1/1/2016 Citation: Wright, E.C., Miles, J.R., Lents, C.A., Rempel, L.A. 2016. Uterine and placenta characteristics during early vascular development in the pig from day 22 to 42 of gestation. Animal Reproduction Science. 164:14-22. Interpretive Summary: A primary cause of fetal death and reduced fetal growth after 35 d of gestation is insufficient placental development. During early gestation, the placenta attaches to the uterine endometrium and establishes the fetal blood supply and nutrient exchange. The attached placenta is composed of a central highly vascular region adjacent to the fetus, a less vascular placental region on either side of the fetus. Necrotic tips develop on the distal end of each placenta between 22 and 42 days of gestation in the region of the placenta that does not attach to the uterine endometrium. We performed a comprehensive evaluation of the uterine-placental interactions and necrotic tip development from 22 to 42 days of gestation in the gilt. Significant morphological changes were observed throughout the placenta and the uterine endometrium from 22 to 42 days of gestation. This work establishes fundamental time points in placental development that correspond to fetal growth and changes in the appearance of the uterine endometrium and placenta that may influence fetal growth and survival. Technical Abstract: The pig, a litter bearing animal, has an epitheliochorial placenta that forms a noninvasive attachment with the uterine endometrium. Insufficient placental development is one of the primary causes of fetal death and reduced fetal growth after 35 d of gestation. Necrotic tips develop at the distal ends of each allantochorion between day 22 and 42 of gestation. During this same period the placenta attaches to the uterine endometrium and establishes fetal blood supplies and nutrient exchange. The attached placenta is composed of a central highly vascular placental (HVP) region adjacent to the fetus, a less vascular placental (LVP) region on either side of the fetus, and necrotic tips (NT). The objective of this study was to comprehensively evaluate uterine-placental interactions and necrotic tip development from 22 to 42 days of gestation in the gilt. Gilts (n = 25) were artificially inseminated at first detection of estrus (day 0) and harvested at 22, 27, 32, 37 or 42 d of gestation. Litter size, 12.1 ± 3.4, was similar (P = 0.86) for all days of gestation. Fetal and placental weight increased (P < 0.05) with day of gestation. The greatest increase (P = 0.02) in placental weight occurred between 37 and 42 d of gestation. The LVP zones had no measureable fold formation for most conceptuses until day 27. Necrotic tips became apparent after 27 d of gestation. Unoccupied areas of the uterus developed folds with changes in endometrial cell size and morphology from day 32 to 42 of gestation. There were limited changes in either fetal growth or placental weight from day 27 through 32 of gestation; however, significant morphological changes occur throughout the placenta and necrotic tips, demonstrating the dynamic architecture of the developing porcine placenta during early gestation. This work establishes fundamental time points in placental development that correspond to fetal growth and microfold formation that may influence fetal growth and survival. |
