Molecular features of reproductive biology associated with fertility in lactating dairy cows

Efficient food production and food availability for a growing world population are some of the greatest challenges facing mankind on this century, and reproduction is a critical component of sustainability in food animal production. Early embryonic mortality in dairy cows is substantial and impairs reproductive efficiency and sustainability of dairy herds. Although predisposition factors for pregnancy loss and reproductive inefficiencies have been identified, the biological mechanisms involved on embryonic losses and even the normal developmental biology in cattle are not understood completely and limit our ability to develop strategies to minimize reproductive inefficiencies. This dissertation discusses the importance of reproduction for the economics of dairy herds and focused on the investigation of key events in ovarian and early developmental biology, their normal biology and how they are impacted by fertility stressors, aiming to find solutions for reproductive inefficiencies that can be applied potentially in commercial dairy herds to improve fertility and consequently sustainability. In addition to a comprehensive analysis of the economics of reproduction to dairy herds, experiments were designed to evaluate key events in ovarian and developmental biology using a holistic approach that combines basic science and applied research. Results are then translated to therapeutic or management strategies that can be used potentially in commercial herds to overcome such challenges. Below is a brief summary of each chapter.;Chapter 1 introduces the dairy industry in the context of modern agriculture and the importance of reproduction for dairy sustainability. Chapter 2 consists of a literature review of the current knowledge in ovarian and early developmental biology in cattle, reproductive management of dairy herds and the major challenges for obtaining success in reproductive efficiency in lactating dairy cows. The review set the stage for the scientific questions and discussions presented in the original articles in the following chapters of this dissertation.;The first original article, Chapter 3, aimed to summarize available information in the literature and to present new analyses regarding the economics of reproduction in dairy herds.;The objectives of the second study, Chapter 4, were to investigate changes in transcriptome of preimplantation conceptuses cells at the onset of elongation and associated changes uterine histotroph composition and endometrial physiology.;The objectives of the third study, Chapter 5, were to evaluate the effects of administering a single or two low doses of slow-release recombinant bovine somatotropin (bST) on hormone concentrations, conceptus development, and fertility in dairy cows.;The objectives of the fourth study, Chapter 6, were to compare development and transcriptome of preimplantation conceptuses 15 days after synchronized ovulation and AI according to the genetic background of the cow and estrous cyclicity at the initiation of the synchronization program.;The objective of the fifth study, Chapter 7, was to investigate the effects of inflammatory diseases occurring before breeding on developmental biology and reproductive outcomes in dairy cows. Five sets of data were compiled to investigate different hypothetical questions associating health status before breeding and reproductive outcomes. Health information for all data sets was comprised of the incidence of retained fetal membranes, metritis, mastitis, lameness, respiratory and digestive problems from parturition until the day of breeding. Retained placenta and metritis were grouped as uterine disease (UTD). Mastitis, lameness, digestive and respiratory problems were grouped as non-uterine diseases (NUTD).;The sixth study, Chapter 8, considers that the interaction between conceptus and maternal immune system can be affected potentially by fertility stressors and contribute to embryonic mortality, and investigates the transcriptome of PBL during the onset of elongation in cows distressed or not by fertility stressors before breeding.;Objectives of the seventh study, Chapter 9, were to identify factors associated with concentrations of AMH in plasma of dairy cows, a marker for ovarian reserve size, and to investigate the relationships between plasma AMH and fertility responses during a 100-d breeding season.;Chapter 10 finalizes this dissertation with a summary of the general conclusions and implications of all studies combined. (Abstract shortened by UMI.).