Increasing length of an estradiol and progesterone timed artificial insemination protocol decreases pregnancy losses in lactating dairy cows.

Our hypothesis was that increasing the length of an estradiol and progesterone (P4) timed artificial insemination (TAI) protocol would improve pregnancy per artificial insemination (P/AI). Lactating Holstein cows (n=759) yielding 31 ± 0.30 kg of milk/d with a detectable corpus luteum (CL) at d -11 were randomly assigned to receive TAI (d 0) following 1 of 2 treatments: (8d) d -10 = controlled internal drug release (CIDR) and 2.0mg of estradiol benzoate, d -3 = PGF2α(25mg of dinoprost tromethamine), d -2 = CIDR removal and 1.0mg of estradiol cypionate, d 0 = TAI; or (9 d) d -11 = CIDR and estradiol benzoate, d -4 = PGF2α, d -2 CIDR removal and estradiol cypionate, d 0 TAI. Cows were considered to have their estrous cycle synchronized in response to the protocol by the absence of a CL at artificial insemination (d 0) and presence of a CL on d 7. Pregnancy diagnoses were performed on d 32 and 60. The ovulatory follicle diameter at TAI (d 0) did not differ between treatments (14.7 ± 0.39 vs. 15.0 ± 0.40 mm for 8 and 9 d, respectively). The 9 d cows tended to have greater P4 concentrations on d 7 in synchronized cows (3.14 ± 0.18 ng/mL) than the 8d cows (3.05 ± 0.18 ng/mL). Although the P/AI at d 32 [45 (175/385) vs. 43.9% (166/374) for 8d and 9 d, respectively] and 60 [38.1 (150/385) vs. 40.4% (154/374) for 8d and 9 d, respectively] was not different, the 9 d cows had lower pregnancy losses [7.6% (12/166)] than 8d cows [14.7% (25/175)]. The cows in the 9 d program were more likely to be detected in estrus [72.0% (269/374)] compared with 8d cows [62% (240/385)]. Expression of estrus improved synchronization [97.4 (489/501) vs. 81% (202/248)], P4 concentrations at d 7 (3.22 ± 0.16 vs. 2.77 ± 0.17 ng/mL), P/AI at d 32 [51.2 (252/489) vs. 39.4% (81/202)], P/AI at d 60 [46.3 (230/489) vs. 31.1% (66/202)], and decreased pregnancy loss [9.3 (22/252) vs. 19.8% (15/81)] compared with cows that did not show estrus, respectively. Cows not detected in estrus with small (<11 mm) or large follicles (>17 mm) had greater pregnancy loss; however, in cows detected in estrus, no effect of follicle diameter on pregnancy loss was observed. In conclusion, increasing the length of the protocol for TAI increased the percentage of cows detected in estrus and decreased pregnancy loss.