| Summary: | Tese de Doutoramento, Ciências Agrárias, 14 de junho de 2018, Universidade dos Açores. Increasing temperature mainly by global warming has been showing rapid environmental temperature chances, unpredictable climatic changes. Increasing temperature has been showing a greater effect on reproductive performance of lactating cows, ultimately affecting dairy economy. Ambient temperatures in subtropical zones during summers affecting cows, as the temperature level were reaching more the upper critical temperature or else above theromonetual zone. Terceira-Azores being considered a dry summer tropical climate, it is important to study the seasonal changes impact on Holstein cows in the islands. Besides this, they still lot unknown factors effecting the heat stress oocytes and embryos, as fertility is a multifactorial problem that affects physiological and cellular functions in several tissues. […]. Aims and Objectives: Increasing environmental temperatures have been showing a greater effect on the fertility of cattle, which eventually affecting global economy of dairy industry. As describe above there is an increasing global warming effect in temperate zone, and subtropical regions , Terceira-Azores (situated in the North Atlantic Ocean: 38° 43' N 27° 12' W) being a dry summer subtropical climate presumed having similar effect. To determine this climatic / Heat stress effect and to study the molecular mechanism involved in reproductive performance of cows following objectives were performed. Objectives Chapter 2: The major objective of this study to evaluate reproductive performances of all day grazing Holstein cows in a warm temperature region of Azores, in relation to environmental stress, but also to determine the in vitro development of oocytes and embryos during cold and warmer months. Apart from this effect of heat shock under different temperatures during in vitro maturation (IVM) of bovine oocytes and further embryonic development after IVF was also evaluated. Chapter 3: To study molecular mechanism/gene expression analysis it is important to stabilize a standardized protocol for the extraction of total RNA from a minimum number bovine oocytes and embryos samples. As so far no proper standardize protocol was descried in specific to Bovine cells. Hence the major aim of this work is to design a standardize protocol which is specific for bovine oocytes and embryos and reliable for the downstream process (Gene amplification and Gene quantification). Chapter 4: To understand the molecular mechanism involved in low fertility rate of cows under heat stress (in vivo and in vitro) the following objective has to be performed. Gene expression studies of developmental genes (Cx43, CDH1, DNMT1 and HSPA14) in different developmental stages (2-cell, 4-cell, morula and blastocyst) of embryos developed from oocytes under prolonged heat shock, as well as oocytes collected during hot and cold seasons has to be studied. Chapter 5: As it is important to understand maternal heat stress factors and to analyze the heat stock condition based on time and exposure, following objectives were performed. Gene expression analysis of kinetic heat shocked oocytes and oocytes matured in the summer and the winter. Chapter 6: An overview and discussion of the results of these studies and their possible implications for the practice and for future research are given.
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