UBC Theses and Dissertations
Strategies to improve ovulation synchronization/timed artificial insemination protocol to increase pregnancy rate in dairy cattle Gordon, Miriam Bronwen
Physiological stressors of high milk production and intensive management systems affect fertility and pregnancy rates (PR) in lactating dairy cows. A field study was conducted on dairy farms in the Fraser Valley of British Columbia to benchmark current reproductive performance and issues that impact local dairy farms. The results indicated a substantial reduction in reproductive performance due to inaccurate estrus detection, fertilization/ovulation failure, and embryonic mortality. Ovsynch timed artificial insemination (TAI) protocol is used for the induction and synchronization of ovulation in cattle, reducing the need for estrus detection. However, PR to Ovsynch TAI are still low. Strategies to modify Ovsynch TAI protocol were investigated in this study to increase PR. In the first experiment, Ovsynch was compared with a pre-synchronization treatment, using PGF₂α before Ovsynch TAI to improve synchronization rates, and to a treatment of GnRH given 6 d after Ovsynch TAI, to reduce embryonic loss. Although no differences in PR were observed between treatments, days in milk in cows and age and weight in heifers affected PR. In the second experiment, the effects of pLH or hCG vs. GnRH in an Ovsynch TAI protocol were compared. Progesterone concentrations in pregnant cows were greater in the hCG group on days 7, 11, and 14, and greater in the pLH group on day 11 after breeding than GnRH group. There were no differences in synchronization rates or PR between treatments. High protein diets have been associated with reduced PR. Therefore, in the third experiment, cows either continued on a typical high protein diet, which was fed from calving, or switched to a lower protein diet, beginning 7 d before Ovsynch TAI and continued until pregnancy diagnosis. First and second lactation cows fed the low protein diet tended to have greater PR than cows fed the high protein diet. There were no differences in synchronization rates and progesterone concentrations between diets. Cows fed the lower protein diet had lower milk urea nitrogen and lower average daily milk production during treatment. Costs associated with treatments, labour, and producer compliance should be considered before recommending ovulation synchronization Ovsynch TAI protocol to dairy producers.
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