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Document Type

Thesis - University Access Only

Award Date

2013

Degree Name

Master of Science (MS)

Department / School

Animal Science

First Advisor

George Perry

Abstract

Estradiol exposure during the preovulatory period has been shown to affect the establishment and maintenance of pregnancy in beef cows. The mechanism by which estradiol affects pregnancy establishment and maintenance has not been well characterized. Previous studies have examined the effects of preovulatory estradiol exposure when mediated through ovulatory follicle size or proestrus length. The objective of this thesis was to examine the role of preovulatory estradiol exposure without the confounding effects of ovulatory follicle size or proestrus length. We hypothesized that preovulatory estradiol is important for embryo survival and pregnancy establishment in beef cows when all other variables were held constant. In order to establish the importance of estradiol during the preovulatory period on embryo survival, ovariectomized cows (n=24) received exogenous hormones to mimic the luteal phase and luteolysis and then received either estradiol cypionate (ECP), estradiol benzoate (EB) or no treatment (CON) according to Latin Square assignment to mimic a preovulatory period. Ovulation was simulated with an injection of gonadotropin releasing hormone (GnRH, 100 μg; d 0). Pregnancy was maintained by exogenous progesterone supplementation. Blood samples were collected in order to characterize circulating estradiol and progesterone. Serum estradiol profiles were different (P < 0. 001) between treatments. Mean serum progesterone concentrations were decreased (P = 0.05) for EB and ECP treated cows compared to CON. Expression of interferon stimulated genes (ISG) was used as a marker for pregnancy on d 17, 19, 21, and 28 and pregnancy-specific protein B (PSPB) was used as a marker for pregnancy on d 22-28. Transrectal ultrasonography was used on d 29 to diagnose pregnancy. When ISG expression was used to predict pregnancy on d 17, 19, and 21, there was no difference between treatments. When PSPB was used to predict pregnancy on d 24, cows that received preovulatory estradiol exposure tended (P = 0.14) to increase the likelihood that pregnancy was predicted. Ultrasonography on d 29 indicated that 4% of CON, 29% of EB, and 21% of ECP treated cows were pregnant. These results indicate greater embryonic survival and pregnancy establishment in cows exposed to estradiol in the preovulatory period.

Library of Congress Subject Headings

Beef cattle -- Embryos -- Mortality.
Pregnancy.
Estradiol.
Ovulation.

Description

Includes bibliographical references (pages 71-82).

Format

application/pdf

Number of Pages

92

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

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