Assisted Reproduction Technologies To Improve Dairy Cattle Reproduction
Over the past decades, dairy cattle reproduction has presented to farmers with several challenges as a consequence of genetic selection for improved milk production traits. These challenges include suboptimal postovulatory responses for timed artificial insemination synchronization protocols. Another example is the metabolic adjustments the preimplantation embryo may undergo in a high producing cow resulting in a high likelihood of early embryo loss. Nevertheless, this is an opportunity to study alternative options to improve pregnancy rates. Assisted Reproduction Technologies (ART) have the potential to solve several issues the modern dairy cow is facing. The progress in the practice of ART has been satisfactory over the last two decades and our understanding about gametes and embryo biology has substantially improved. Embryo transfers using in vitro produced embryos (IVP) might certainly have an advantage over conventional breeding methods since ovulation, fertilization and early embryonic stages would be bypassed thereby enhancing the likelihood of embryo implantation and hence improved conception rates. However, there are several challenges to producing good quality embryos in vitro due to difficulties in emulating the natural oviduct microenvironments that the preimplantation embryo is experiencing several physiological changes en route to the uterus. The objectives of this work were to review current literature in regard to mammalian preimplantation embryo production in vitro with emphasis in bovine species and to study the effect of metabolic regulators (MR) on embryo development as well as using new methods to recover better quality sperm especially when using sex-sorted semen. Chapter Two is an extensive review of the IVP process in mammalian species with emphasis on the bovine embryo. Metabolic processes during oocyte in vitro maturation, sperm interactions during fertilization and in vitro cultures of different preimplantation embryo stages are reviewed. Special attention was devoted to the metabolic switch from low to high glucose uptake and metabolism occurring at the morula stage. Chapter Three is a systematic study of the effects of conjugated linoleic acid (CLA) isomers on embryos produced in vitro. Inclusion of 100 [mu]M CLA- cis 9, trans 11 during embryo culture 36 hrs before cryopreservation resulted in embryos with higher survival and better developmental rates post-thaw when compared to other groups. Chapter Four presents a study about the effect of phenazine ethosulfate (PES) and 2, 4-dinitrophenol (DNP) on embryo development at the morula stage to enhance glucose uptake and metabolism to improve embryo developmental rates. Combination of 0.3 [mu]M PES and 10 [mu]M DNP resulted not only in higher embryo development and better quality but also embryos more resistant to cryopreservation procedures. Chapter Five describes a study of the effect of four colloidal-based sperm washes (Percoll, Old Bovipure, New Bovipure and Androcoll-B) on embryo development and quality. The International Embryo Transfer Society regulations strictly indicate that bovine embryos produced in vitro should be originated from sperm that has been recovered by silane-coated silica particles colloids when fractionation methods are used due to the debatable toxic effects of Percoll. Results from these experiments showed that embryos derived from sperm recovered by New Bovipure and Androcoll-B achieved higher blastocyst rates than Percoll and Old Bovipure groups. In addition, as a followup the effects of MR were evaluated on embryos originated from X-sorted semen. Interestingly, PES and DNP supplementation resulted in delayed development and poorer morphology in this embryos compared with untreated counterparts. Glucose uptake threshold may be lower in female embryos and/or they may have a different substrate preference as compared to male embryos. Our contribution to science may provide information for a better understanding of IVP and help shape the direction of future research. More importantly, it may provide the basis for production of better quality embryos originated from genderselected semen with more chance of survival to term, thereby improving conception rates in dairy cattle.
in vitro; bovine embryo; metabolism
Butler, Walter Ronald
Gilbert, Robert Owen; Van Amburgh, Michael E; Suarez, Susan Stevens
Ph.D. of Animal Science
Doctor of Philosophy
dissertation or thesis