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Ovarian dysfunction and embryonic mortality are one of the major causes limiting fertility and reproductive efficiency in dairy cows. The overall aim of the present investigation is to study physiological mechanisms and risk factors leading to ovarian dysfunction and late embryonic mortality in cows managed in high input environments. The research will be to address the question of why some high producing cows maintain good fertility and others do not. Our overall hypothesis is that some cows and breeds are better adapted to high milk production and therefore are able to maintain better reproductive efficiency and health under intensive management conditions. Specific objectives of the study are: 1) To quantify the incidence rate of ovarian dysfunction, late embryonic mortality, silent heat, and the occurrence of clinical disease in Estonian Holstein and Estonian Red breed cows managed in high input environments; 2) To establish causative factors leading to ovarian dysfunction and late embryonic mortality in Estonian Holstein and Estonian Red breed cows managed in high input environments; 3) To determine the effect of breed and genetic merit on the established factors leading to ovarian dysfunction; 4) To study the effect of mastitis and other clinical disease on luteal function, anovulation, conception rate, and late embryonic mortality.The proposed study is the first comparative investigation in which the effect of multiple factors (breed, genetic merit, milk production, milk composition, disease) on ovarian and luteal function and embryonic mortality are studied in different dairy breeds and cows of different genetic merit that are managed in the high input environments. The knowledge gained will enable scientifically sound action plans for improving reproductive efficiency in dairy cattle to be established. |