Semester

Summer

Date of Graduation

2009

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Matthew E. Wilson.

Abstract

Placental efficiency, defined as fetal weight divided by placental weight, has been shown to be involved in litter size. Breeds that are more prolific (12-13 pigs per litter) have feto-placental units with higher placental efficiencies. However, domestic commercial breeds have much smaller litters of about 9.5 pigs per litter. Placental size is vastly different, such that high placental efficiency pigs have smaller, more vascularized placentae. Even within an individual litter two piglets with similar body weights may be grown on placentae that are different in size. The placenta of the least efficient feto-placental unit may be up to 50% bigger than the placenta of the most efficient feto-placental unit. The fetus relies on the placenta for the transport of nutrients from the dam to the fetus. Both the size of the placenta, and the amount of vasculature of the placenta and endometrium, are important for the transport of nutrients to the fetus. Therefore, the objectives of the current experiment were to determine the mRNA expression of nutrient transporters in both the placenta and endometrium and to see if a relationship existed between placental efficiency and the expression of nutrient transporters and vascular density. Gilts were bred by artificial insemination 12 and 24 hours following the detection of estrus and at this time were randomly assigned to be ovario-hysterectomized on days 70, 90 or 110 of gestation. At the time of ovario-hysterectomy, placental and endometrial samples were collected for the determination of nutrient transporter expression and vascular density. Other fetal characteristics were recorded, such as fetal weight, placental weight, and placental efficiency. Placental efficiency and the range of placental efficiency increased as gestation proceeded to day 90 and 110, with a near three- and four-fold increase, respectively. Fetal and placental weights were positively correlated throughout gestation. Placental weights were negatively correlated with placental efficiency throughout the final third of gestation. The vascular densities of the placenta and endometrium were positively correlated for days 70, 90 and 110 of gestation. Late in gestation, placental vascular density had negative relationships with both placental and fetal weights. However, no relationship was observed between placental efficiency and vascular density. Also, no relationships were detected between placental efficiency and the mRNA expression of nutrient transporters. There were also no interactions observed between expression of nutrient transporters and day of gestation. Day of gestation, however, was found to be an important influence on placental efficiency. Placental vascularity has been shown to influence placental efficiency in the past, though it did not here, there have also been instances where placental vascular density was not affected by selection for increased placental efficiency. The RNA message for the protein transporter may not be an effective way to estimate actual transport of nutrients or the types of nutrients being transported.

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