Influence of ovarian dynamics on fertility in dairy cows: a timed artificial insemination protocol with 12-day progesterone-releasing intravaginal device insertion and ovulation induction with estradiol benzoate

The purpose of this study was to investigate ovarian dynamics and fertility during a labor-saving timed artificial insemination (TAI) protocol using a progesterone-releasing intravaginal device (PRID) with an estradiol benzoate (EB) capsule. Forty-eight lactating dairy cows with ovarian echogenic structures considered to be corpus luteum (CL) received PRID for 12 days (d0-12), EB injection on d13, and TAI on d14. Ovulation was monitored on d14-16, and 13 cows without confirmed ovulation by d15 received a second AI on d15. Pregnancy was confirmed in 21 cows, including 18 by TAI only and 3 after re-insemination (43.8%). Among 45 cows (excluding 3 that conceived after re-insemination), pregnancy rates (P/TAI) were 60% (12/20) for cows whose CL disappeared by d5 (early luteolysis), 38.5% (5/13) for those whose CL disappeared on d6-14 (late luteolysis), and 8.3% (1/12) for those whose CL remained detectable on d14 (incomplete luteolysis). Cows with incomplete luteolysis had lower fertility than those with early luteolysis (odds ratio, 0.06; 95% confidence interval, 0.01-0.41; P=0.002). P/TAI did not differ significantly between cows with follicular turnover (emergence of new follicular wave) on d2-5 (42.3%, 11/26) and those without (36.8%, 7/19). Ovulation was synchronized in 91.7% (44/48) within 3 days after EB injection. Four anovular cows had a large CL (≥20 mm) on d14. Thus, the 12-day PRID plus single EB protocol was practical. However, ovulation synchronization failed in 4 cows with incomplete luteolysis.