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Document Type

Thesis - University Access Only

Award Date

2014

Degree Name

Master of Science (MS)

Department

Animal Science

First Advisor

George Perry

Abstract

In cattle, circulating concentrations of estradiol peak approximately 36 h before ovulation (Chenault et al., 1975) and a rise in serum concentrations of estradiol initiates estrus behavior in females (Allrich, 1994). Previous research has reported that cows expressing estrus prior to fixed-time AI (TAI) have increased preovulatory concentrations of estradiol (Perry and Perry, 2008a) and a 27% greater conception rate compared with those not exhibiting estrus (Richardson et al., 2014). Estradiol is responsible for many other physiological processes required for the establishment and maintenance of pregnancy and failure to produce sufficient concentrations of estradiol may impede these processes and the reproductive success of a female. Therefore, to provide insight into potential mechanisms of regulation of estradiol production from the dominant follicle, ovaries were collected and examined from high estradiol and low estradiol cows (first experiment; Chapter 3). Cows with greater circulating concentrations of estradiol during the preovulatory period were found to have an increased ability to produce estradiol and an enhanced secondary to tertiary follicle transition. While differences in ovarian function were observed between treatment groups (Chapter 3), our next objective was to determine if estradiol production from the dominant follicle could be stimulated with administration of exogenous gonadotropin releasing hormone (GnRH; second experiment; Chapter 4). Treatment with exogenous GnRH increased circulating concentrations of estradiol, but not as quickly or to the magnitude of the HighE2 animals. One mechanism reported to be influenced by estradiol is regulation of the uterine environment. Estradiol regulates changes in uterine pH (Perry and Perry, 2008a, b) which have been shown to prolong the viable lifespan of sperm (Jones and Bavister, 2000) and increase sperm motility (Goltz et al., 1988). Estradiol has also been reported to improve embryo quality and viability and may be a result of endometrial remodeling and uterine secretions to provide an environment conducive to pregnancy. The objective of this experiment was to discover if expression of estrus impacted sperm transport and early embryonic development (third experiment; Chapter 5). Estrous expression increased sperm transport and enhanced embryo development.

Library of Congress Subject Headings

Beef cattle -- Embryos
Estrus
Estradiol
Pregnancy
Ovulation

Description

Includes bibliographical references (pages 81-92)

Format

application/pdf

Number of Pages

103

Publisher

South Dakota State University

Rights

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

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