For many cattle operations, profitability depends on the success of reproductive management programs. Opportunities for improving fertility exist within the numerous challenges related to reproductive management. Non-conventional, creative tools for reproductive management could help producers overcome these challenges. In an effort to produce information that could be used to improve reproductive performance of cattle, the following studies were undertaken. The objectives of these studies were threefold: to determine whether GnRH administered as an epidural injection causes ovulation in healthy cows and heifers, to evaluate whether the follicular environment (specifically, follicle fluid) surrounding the oocyte during the maturation phase affects the ability of the cumulus-oocyte complex to progress through early embryonic development, and to investigate the relative effects of estradiol and progesterone on oocyte maturation and early embryo development.
Ability of GnRH to elicit an ovulatory response when administered as an epidural was evaluated in crossbred angus cows and heifers. The preliminary study evaluated this route of administration in crossbred angus cows. Animals were assigned randomly to either intramuscular or epidural administration, and ovaries were visualized via transrectal ultrasound every 6 h until ovulation of the dominant follicle. Results indicated that epidural administration of GnRH was able to trigger an ovulatory response, but timing of ovulation was not measured. The main experiment evaluated incidence of ovulation, time to ovulation, and ovulatory follicle size in crossbred angus heifers administered GnRH either epidurally or intramuscularly. Heifers were randomly assigned to treatment and ovaries were visualized every 4 h via transrectal ultrasound until ovulation of the dominant follicle. Results indicated that epidural administration of GnRH was able to elicit an ovulatory response in heifers, and the timing of ovulation and ovulatory follicle size was not different between administration route. Further investigation is needed to determine if characteristics of the ovulatory response (such as the luteinizing hormone surge) and circulating concentrations of GnRH are altered by epidural administration, which may impact fertility.
GnRH administration is standard practice in many estrous synchronization programs. For fixed-time artificial insemination programs, the detection of estrus prior to insemination has been shown to improve conception and decrease early embryonic loss. The impact of behavioral estrus expression on the oocyte and early embryo were evaluated. Oocytes were matured in vitro in follicle fluid collected from synchronized cows who were classified as having expressed behavioral estrus or not expressing estrus. Embryo cleavage was not affected by estrus expression, but there was a tendency for improved blastocyst development in embryos matured in follicle fluid from animals who had expressed estrus. Cell number was not affected by estrus expression, but future research is needed as to the effect on oocyte acquisition of competence and early embryonic development.
Despite the progress that has been made in culture conditions for in vitro produced embryos, developmental capacity following fertilization is limited at best, with only around one-third of oocytes placed into maturation resulting in viable embryos. During in vivo maturation, the oocyte undergoes final maturation within the follicle, surrounded by a changing microenvironment of estradiol and progesterone. Although the effects of steroids on oocyte development in vitro have been studied on an individual basis, a direct comparison between the ratio of estrogen and progesterone relative to follicle size has not been investigated Effects of steroid hormones estradiol and progesterone on oocyte maturation and early embryonic development were evaluated. Oocytes were matured in vitro in media supplemented with either estradiol, progesterone, or a combination of estradiol and progesterone. Oocytes were fertilized after maturation and cultured for 7 d until development to blastocyst stage. Addition of estradiol alone did not support oocyte maturation or early embryonic development in vitro, and a combination of estradiol and progesterone exhibited an inhibitory effect on oocyte maturation and early embryonic development. Addition of progesterone alone resulted in improved development when compared with estradiol alone or a combination of estradiol and progesterone.
These results indicate that efficiency of reproductive management programs is controlled by multi-faceted factors and opportunities for improvement of reproductive outcomes exist in all of these factors. Although ovulation can be elicited via epidural administration, the impact of this ovulatory trigger on fertility requires further investigation. Display of estrus after synchronization for fixed-time artificial insemination improves conception and decreases early embryonic loss and has a may improve blastocyst development. This effect on early embryo development could be the focus of future research, further improving fertility and possibly the efficacy of in vitro embryo production. Steroid hormones play crucial roles in oocyte competency and the addition of progesterone during in vitro maturation improves development compared with estradiol alone or a combination of estradiol and progesterone. / Ph. D. / Reproductive success is critical for economic sustainability for many cattle operations. Creative tools for fertility management could help cattle producers overcome many challenges to fertility. In an effort to produce information that could be used to improve reproductive performance of cattle, the following studies were undertaken. The objective of these studies was to determine whether hormone administration as an epidural injection causes ovulation in healthy cattle (young and mature cattle assessed). Additionally, the second study evaluated whether the follicle (fluid-filled compartment surrounding the egg on the ovary) environment affects the female egg prior to ovulation, and the early embryo after fertilization. Finally, the third study looked at the impact of follicle fluid and specific hormones on embryo growth. An experiment was conducted in cows and heifers to determine if administering a hormone as an epidural injection, as opposed to conventional methods, could cause ovulation of the follicle. Animals received either an intramuscular or epidural hormone injection, and the ovaries of the animals were observed on an ultrasound until the follicle ruptured, releasing the egg. Epidural administration of the hormone was indeed able to trigger the rupture of the follicle. Hormone administration is standard practice in many cattle fertility programs. To maximize fertility, animals need to come into “heat” or estrus (period of sexual receptivity). Coming into heat is important for fertility in the female as it is indicative of impending ovulation and preparation of the egg for fertilization. In some reproductive management systems, reproductive cycles can be controlled in ways that deemphasize the need for behavioral estrus. Recent reports have suggested that animals in these systems that exhibit behavioral estrus are more fertile, as it makes it more likely for the female to conceive and stay pregnant compared to females who do not come into heat. The impact of heat on the female egg and early embryo of the cow has not been investigated. To evaluate the impact of heat on embryos, eggs were taken from the ovary of the cow and matured in a cell culture lab overnight in media containing fluid taken from the follicles of animals who came into heat, and animals that did not come into heat. The eggs were then fertilized, and embryos developed. There was only a tendency for improvement in embryo development for those matured in fluid from animals in heat compared with animals not in heat. When growing embryos in a culture lab, success rates are lower than embryos developing in the animal. When the egg is being prepared for release, it goes through important maturation steps to enable fertilization and eventual growth into a calf. Hormones in the follicle fluid facilitate maturation, and the conditions in the follicle are not easily replicated in the lab. The addition of these critical hormones to the lab conditions may help facilitate improved development in lab-produced embryos. Two hormones (estrogen and progesterone) were added to follicle fluid that was used in the lab culture environment to determine their effect on embryo growth. When progesterone was added, embryos grew well, matching the development rate of the control medium. When estrogen was added, embryos experienced poor development. Neither resulted in embryo development that exceeded the control medium. These results indicate that control of reproduction in cattle is complex, and multiple opportunities exist to improve fertility. Future research on how the oocyte and embryo react to their environment is needed and will facilitate further improvement of reproductive management systems in cattle. Improved reproductive management will enhance efficiency, sustainability and profitability of cattle production systems.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/85863 |
| Date | 15 November 2018 |
| Creators | Harl, Audra Whitney |
| Contributors | Animal and Poultry Sciences, Rhoads, Michelle, Ealy, Alan D., Cockrum, Rebecca, Saacke, Richard G., Lee, Kiho |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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