Endocrine and nutritional factors affecting fertilization and early embryo development in dairy cows

The main scope of the present dissertation was to determine endocrine and nutritional factors with potential to impact fertility by improving fertilization, early embryo development and uterine function. One study was conducted to assess the effects of follicle dominance length and estradiol during proestrus on fertilization and early embryo development. Lactating cows had their estrous cycle pre-synchronized and were randomly allocated into one of four synchronization treatments expected to differ in length of the ovulatory follicle dominance and estradiol during proestrus. Extending the period of follicle dominance did not alter fertilization, but reduced embryo quality. Embryo quality was compromised when the dominance of the ovulatory follicle was slightly extended. The effects of concentration of progesterone during the ovulatory follicle growth on early embryo development as well as its delayed effects on the subsequent estrous cycle were observed in two complementary studies. Reducing progesterone concentrations during the Ovsynch program altered estradiol concentrations and follicular dynamics during follicle development, but resulted in no difference in fertilization rates and only minor changes in embryo quality. In addition, reduced concentration of progesterone during Ovsynch altered follicular fluid composition and exacerbated PGF2alpha , release in the subsequent estrous cycle. Nutraceuticals are dietary ingredients used therapeutically to target specific biological responses. The effects of linoleic acid and a blend of trans octadecenoic acids, and of an organic source of selenium fed during the pre- and post-partum were evaluated in two separate studies. In addition to the effects on fertilization and early embryo quality, overall health during the transition period and uterine immune status were evaluated. Feeding a more unsaturated source of fatty acid improved fertilization and embryo development in lactating dairy cows, despite similar indicators of metabolic status. However, feeding an organic source of selenium as Se-yeast was not effective to improve disease resistance, uterine health, fertilization and embryo quality in early lactating dairy cows compared with an inorganic source of selenium. In conclusion, decreasing dominance length, increasing concentration of progesterone during follicle growth, and feeding a blend of unsaturated fatty acids have the potential to improve fertility by promoting early embryo development and modulating PGF2alpha release.