Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

School of Animal Science

First Advisor

Robert A. Godke

Second Advisor

Charles R. Short

Abstract

Information gained by studying follicular wave and endocrinological patterns of pregnant mares, may be useful in understanding reproductive wastage, infertility, control of the estrous cycle and physiological function of equine chorionic gonadotropin (eCG). Furthermore, supplementary follicular development, characteristic of the early equine pregnancy, may be used to harvest oocytes for gamete intrafallopian tube transfer and in vitro fertilization (IVF) procedures. The objectives of this study were to: characterize follicular wave patterns during the first half of the equine pregnancy; relate follicular development patterns to serum levels of estradiol-17$\beta$, progesterone, FSH and eCG; evaluate the effect of fetal genotype on follicular dynamics; evaluate the repeatability and safety of transvaginal oocyte recovery procedures on pregnant mares; evaluate the viability of recovered oocytes by a novel IVF procedure; and test the applicability of this aspiration and IVF technology in the Burchell's zebra. Three follicular aspiration treatments were applied to mares pregnant with horse and mule fetuses. The most striking difference in follicular development patterns was observed between mule and horse pregnancies. Mares pregnant with mules did not have an equivalent follicular activity peak corresponding to peak levels of mule eCG as did mares pregnant with horse fetuses. Mares carrying horse pregnancies had markedly reduced follicular activity during the post-eCG period when compared with that of mule pregnancies. Results presented suggest that the phenomenon of reduced follicular activity in mares carrying horse fetuses involves desensitization of the ovary by exposure to high concentrations of horse eCG and a direct inhibitory effect of horse eCG on FSH. Although repeated aspiration of follicles influenced follicular wave parameters and hormone profiles, the ongoing pregnancy was not endangered. Zona-drilled, IVF oocytes from pregnant mares were cultured to morula and blastocyst stages, indicating that these oocytes were viable. To our knowledge, this is the first report of successful IVF of equine oocytes collected from pregnant donors. The oocyte aspiration procedure was equally effective, safe and repeatable in zebra mares. The oocytes of zebra mares similarly produced blastocyst-stage embryos after exposure to the in vitro maturation, IVF and in vitro culture procedures developed for horse oocytes.

Pages

293

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