Semester

Summer

Date of Graduation

2003

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Physiology, Pharmacology & Neuroscience

Committee Chair

E. Keith Inskeep.

Abstract

Timing and factors associated with late embryonic and fetal loss in the ewe were examined with ultrasonography. In study one, pregnancy diagnosis and counts of embryos were conducted on days 25, 45, 65, and/or 85 of gestation and compared to lambs born at term. Preliminary results indicated that more potential offspring were lost during fetal development than during late embryonic development. Approximately 18% of ewes experienced late embryonic and fetal loss and 20% of embryos or fetuses were lost from day 25 to term. Losses of potential offspring were continuous throughout gestation and approximately 3% of embryos present on day 25 were lost during each 20-day interval of pregnancy beyond that point. More ewes lost one, but not all, embryos or fetuses. The pattern of late embryonic and fetal losses during the late breeding season was similar to anestrous or transitional periods. Breeding season and service period did not affect losses during any stage of pregnancy. Late embryonic and fetal mortality was not related to temperature-humidity index. Breed differences affected the proportion of embryos or fetuses lost and concentrations of progesterone, estradiol, and VEGF. A threshold concentration of maternal progesterone was necessary for maintenance of pregnancy and survival of individuals within a litter might be related to a role of vascular endothelial growth factor in placentation. In study two, pregnancy diagnosis was conducted on days 18 and 19 of gestation to determine effects of allantois expansion on late embryonic and fetal mortality. Pregnancy retention from day 18 to term and the number of lambs born per ewe pregnant on day 18 did not differ between ewes with embryos having an expanded or non-expanded allantois. Number of lambs born per ewe lambing tended to be greater in ewes with one non-expanded embryo on day 18. Allantoic expansion on day 18 was not associated with location of corpora lutea. A single embryo was more likely to be lost if it failed to undergo allantoic expansion by day 18 of gestation.

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