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Effect of Inducing High or Low Progesterone Concentrations During Ovulatory Follicle Development on Double Ovulation and Fertility of Lactating Dairy Cows
One objective of my dissertation work was to determine the effect of high vs. low progesterone during pre-dominance and dominance phase of ovulatory follicle development on follicular dynamics and fertility of lactating dairy cows. Cows that ovulated a d 7 first wave dominant follicle and started a second follicular wave were assigned to treatments. Progesterone was manipulated to reach high (H) or low (L) serum concentrations during the pre-dominance phase (0 to 4 d of the wave) and dominance phase (5 to 7 d of the wave) creating 4 treatments: HH, LL, HL, and LH. Luteolysis was induced with PGF2α on d 7 of the wave and ovulation was induced with GnRH 56h after PGF2α. Cows (n=558) received AI 16 h following GnRH. Ovaries were evaluated by ultrasonography prior to and during treatment. Pregnancy was determined 23 and 28 d post-AI by serum concentrations of pregnancy-specific protein B (PSPB), 35 and 56 d post-AI by ultrasonography and 117 d and 194 d by milk concentrations of PSPB. Calving data was also collected. Percentage of cows with double ovulations to the last GnRH was greater in LL (49%) compared with HH, HL and LH (12, 34, and 34% respectively). Pregnancy/AI 23 d post AI was 49, 60, 61, and 66% for HH, HL, LH, and LL, respectively, and was greater for LL than HH cows. Full term pregnancies/AI was 33, 43, 43, and 43% for HH, HL, LH, and LL, respectively, and was not different between treatments. Pregnancy losses between 35 and 56 d post AI was 2, 10, 5 and 15% for HH, HL, LH, and LL, respectively, and was greater for LL than HH. Cows that had double ovulation after the last GnRH had greater pregnancy/AI 23 d (73 vs. 53%) and full term pregnancy/AI (38 vs. 47%) compared to cows with single ovulation. Pregnancy losses between 35 and 56 d after AI was greater in cows with double ovulation compared to cows with single ovulation (4 vs. 13%). In cows with double ovulation, majority of pregnancy losses between 35 and full term were in cows with ovulations on the same ovary. In summary, low P4 during development of the ovulatory follicle increased the percentage of cows with double ovulations and P/AI 23 d post AI, but decreased embryonic survival between 35 and 56 d post AI. Most losses post-attachment were likely due to unilateral twins.
Keywords: progesterone, dairy cows, fertility, follicle