Degree

Doctor of Philosophy (PhD)

Department

Veterinary Clinical Sciences

Document Type

Dissertation

Abstract

While the in vitro production of equine embryos (IVEP) has exponentially advanced over the past decades, overall success remains limited, with major bottlenecks at every stage of the process. Recently, the success of conventional in vitro fertilization with high oocyte to embryo conversions redirects the spotlight to the limited availability of developmentally competent oocytes for fertilization procedures in the equine species. Pre-maturation treatments have been suggested to improve developmental competence with storage at room temperature (holding) being the most commonly applied treatment for equine oocytes. The goal of this dissertation was to evaluate the effects of holding on markers of nuclear, cytoplasmic and molecular oocyte maturation; and developmental potential through early embryonic development kinetics and quality. Expanded and/or compact COCs were collected from abattoir derived ovaries or ovum pick-up and placed into in vitro maturation (IVM) immediately after collection or following 18-24 hours of holding. Cumulus cell morphology influenced initial presentation of nuclear and cytoplasmic markers, as well as chromatin progression during holding and IVM. Holding did not enable the progression of cytoplasmic markers but allowed for chromatin condensation maintaining meiotic arrest. Holding-induced meiotic arrest may be a result of temperature-impaired microtubule dynamics. Furthermore, holding induced nuclear-cytoplasmic asynchronies that were mostly restored during IVM according to initial developmental competence. Holding was associated with progression into transcriptional silencing after removal from the follicular environment, with immature and in vitro matured oocytes exposed to holding presenting minimal changes in transcriptomic profile. Changes in transcripts abundance during IVM may reflect the activation of compensatory mechanism to mitigate holding-induced nuclear-cytoplasmic asynchronies. The effects of holding seem to extend into in vitro culture, exacerbating limitations of less developmentally competent oocytes leading to their negative selection. Holding does not affect in vitro success markers such as maturation and blastocyst rates. Negative selection occurs with a population of COCs unequipped to overcome current in vitro conditions regardless of treatment. Further studies are necessary to investigate the effects of holding on other components of oocyte maturation and embryonic development, and to improve pre-maturation approaches and in vitro outcomes.

Date

1-21-2026

Committee Chair

Carlos Pinto

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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