The objective was to determine the effect of exogenous progesterone (P4) in a timed artificial insemination (TAI) protocol initiated at 2 different times post-AI on pregnancies per AI (P/AI) in lactating dairy cows. Cows (n=1,982) in 5 dairy herds were assigned randomly at a nonpregnancy diagnosis 32 ± 3 d post-AI to 1 of 4 resynchronization (RES) treatments arranged in a 2 × 2 factorial design using the Ovsynch-56 (GnRH, 7d later PGF2α, 56 h later GnRH, 16 h later TAI) protocol. Treatments were as follows: cows initiating RES 32 ± 3 d after AI with no supplemental P4 (d 32 RES-CON; n=516); same as d 32 RES-CON plus a controlled internal drug release (CIDR) insert containing P4 at the onset of Ovsynch-56 (d 32 RES-CIDR; n=503); cows initiating RES 39 ± 3 d after AI (d 39 RES-CON; n=494); and same as d 39 RES-CON plus a CIDR (d 39 RES-CIDR; n=491). Cows were inseminated if observed in estrus before TAI. The P/AI was determined 32 and 60 d after TAI. In a subgroup of cows (n=1,152), blood samples were collected and ovarian structures examined by ultrasonography on the days of the first GnRH (G1) and PGF2α of Ovsynch-56. Percentage of cows with a corpus luteum (CL) at G1 was unaffected by timing of treatments, but percentage of cows with a CL at PGF2α was greater for d 32 than for d 39 cows (87.9 vs. 79.4%). In addition, percentage of cows with P4 ≥ 1 ng/mL at G1 was unaffected by timing of treatments, but was increased for d 32 compared with d 39 RES cows on the day of the PGF2α of the RES protocols (86.5 vs. 74.3%). Treatment did not affect ovulation to G1 or P/AI 32 d after RES TAI (d 32 RES-CON=30.1%, d 32 RES-CIDR=28.8%, d 39 RES-CON=27.5%, d 39 RES-CIDR=30.5%). A greater percentage of d 39 RES cows underwent premature luteolysis during the RES protocol compared with d 32 RES cows. An interaction was detected between day of RES initiation and CIDR treatment, in which the CIDR increased P/AI 60 d after TAI for d 39 (CON=23.7% vs. CIDR=28.0%), but not for d 32 (CON=26.9% and CIDR=24.2%) cows. Pregnancy loss was unaffected by treatment. In addition, cows had improved P/AI 60 d after TAI when they received a CIDR and did not have a CL (CON-CL=28.2%, CON-No CL=19.2%, CIDR-CL=27.0%, and CIDR-No CL=26.5%) or had P4 <1 ng/mL (CON-High P4=27.8%, CON-Low P4=15.0%, CIDR-High P4=25.0%, and CIDR-Low P4=29.4%) at G1, but not if a CL was present or P4 was ≥ 1 ng/mL at G1. In conclusion, addition of a CIDR insert to supplement P4 during the RES protocol increased P/AI for cows initiating RES 39 ± 3 d after AI but not 32 ± 3 d after AI.

Effect of treatment with gonadotropin-releading hormone (GnRH)or 4 doses of human chorionic gonadotropin (hCG)on ovulatory response in lactating Holstein cows

The objectives of this study were to evaluate effects of 2 resynchronization protocols beginning at different intervals after artificial insemination (AI) on the pattern of return to estrus, ovarian responses, and pregnancy per AI (P/AI) to reinsemination. Lactating cows from 2 dairies, located in Texas (n=2,233) and Minnesota (n=3,077), were assigned to 1 of 4 timed AI (TAI) protocols 17 ± 3 d after AI. All cows were examined for pregnancy 31 ± 3 d after previous AI. Cows assigned to early Ovsynch56 (E-OV56) or OV56 received the Ovsynch56 protocol starting 24 or 31 d after AI, respectively. Cows assigned to early GnRH-GnRH-PGF(2α)-GnRH (E-GGPG) or GGPG received a presynchronizing GnRH injection 17 or 24 d after AI, respectively, 7 d before the start of the Ovsynch56 protocol. Cows observed in estrus after enrollment were inseminated on the same day. Ovaries were examined and blood was sampled for progesterone concentration on the day of first GnRH and PGF(2α) injection of the Ovsynch56 protocol. Pregnancy was diagnosed at 31 and 66 d after resynchronized AI. On the day of the first GnRH injection of the TAI, a higher percentage of cows on E-GGPG and GGPG protocols had a corpus luteum (E-GGPG=83.8, GGPG=91.2, E-OV56=80.4, and OV56=75.5%) and progesterone concentration >1 ng/mL (E-GGPG=62.5, GGPG=76.0, E-OV56=53.6, and OV56=60.8%) than cows assigned to other protocols. However, the percentage of cows ovulating to the first GnRH injection of TAI was not affected by treatment. Fewer E-GGPG and more OV56 cows were reinseminated in estrus (E-GGPG=23.7, GGPG=49.0, E-OV56=41.6, and OV56=57.6%). Treatment did not affect P/AI at 31 or 66 d for cows reinseminated in estrus. However, cows reinseminated in estrus had greater P/AI at 31 (40.0 vs. 27.5%) and 66 d (36.0 vs. 23.9%) than cows completing the TAI protocols. Among cows completing the TAI protocols, initiation of GGPG at 24 d after AI increased, whereas initiation of Ovsynch56 at 24 d after AI decreased P/AI at 31 d after reinsemination (E-GGPG=30.6, GGPG=28.3.0, E-OV56=22.3, and OV56=28.7%). Pregnancy per AI did not differ across treatment at 66 d after TAI (E-GGPG=26.6, GGPG=24.4, E-OV56=20.0, and OV56=24.1%). Overall, type of resynchronization protocol and protocol initiation time did not affect P/AI 66 d after reinsemination (E-GGPG=29.7, GGPG=30.5, E-OV56=26.1, and OV56=30.4%). In conclusion, GGPG resynchronization protocols and initiation of resynchronization protocol 24 d after AI reduced the number of cows reinseminated in estrus but neither the timing of initiation of resynchronization nor presynchronization with GnRH affected overall P/AI.

Objectives were to evaluate the effect of 2 analogs of PGF_2α (cloprostenol vs. dinoprost) and 2 doses (1 injection vs. 2 injections) on luteolysis, follicle diameter, hormonal concentrations, and time to ovulation in dairy heifers. Holstein heifers were fitted with automated estrus detection devices and had their estrous cycle synchronized using PGF_2α and an intravaginal insert containing progesterone. Heifers detected in estrus were blocked by weight and randomly assigned to 1 of 4 treatments in a 2 × 2 factorial arrangement: cloprostenol on d 7 after estrus (CLOx1; n = 45), cloprostenol on d 7 and 8 after estrus (CLOx2; n = 41), dinoprost on d 7 after estrus (DINx1; n = 43), or dinoprost on d 7 and 8 after estrus (DINx2; n = 44). Treatment with the first injection of PGF_2α was defined as experiment d 0. Area and blood flow of corpus luteum (CL) and diameter of follicles >5 mm were recorded every 12 h from d 0 to estrus and every 6 h thereafter until ovulation. Blood was sampled every 6 h from d 0 until ovulation. Heifers treated with cloprostenol had shorter interval to luteolysis (± SEM; CLOx1 = 23.5 ± 2.2, CLOx2 = 22.9 ± 2.2, DINx1 = 32.6 ± 2.7, DINx2 = 26.4 ± 2.1 h); however, time to ovulation was not affected by treatment. A smaller proportion of heifers treated with a single injection of PGF_2α underwent luteolysis compared with heifers treated with 2 injections (CLOx1 = 84.6 ± 6.2, CLOx2 = 100.0 ± 0.0, DINx1 = 59.7 ± 9.8, DINx2 = 96.3 ± 2.7%). Proportion of heifers that ovulated was smaller for DINx1 compared with other treatments (CLOx1 = 88.8 ± 5.1, CLOx2 = 100.0 ± 0.0, DINx1 = 55.2 ± 9.7, DINx2 = 94.4 ± 3.4%). Ovulatory follicle diameter was larger for DINx1 (18.2 ± 2.7 mm) compared with DINx2 (17.4 ± 2.7 mm), whereas dose did not affect the diameter of the ovulatory follicle in heifers treated with cloprostenol (CLOx1 = 17.6 ± 2.7 vs. CLOx2 = 17.8 ± 2.8 mm). Among heifers that underwent luteolysis, progesterone concentrations from 18 to 36 h after treatment were lesser in heifers treated with cloprostenol compared with those treated with dinoprost. Type of PGF_2α did not affect progesterone concentrations past 36 h from treatment; however, heifers treated with 2 PGF_2α injections had lesser progesterone concentrations and CL blood flow from 36 to 72 h after treatment compared with heifers that received a single PGF_2α injection.

Our objective was to compare the effect of treatment with GnRH at the first treatment (G1) of the Breeding-Ovsynch portion of a Double-Ovsynch (DO) protocol with human chorionic gonadotropin (hCG) on pregnancies per artificial insemination (P/AI) in lactating dairy cows. In experiment 1, lactating dairy cows (n = 1,932) submitted to a DO protocol for first timed artificial insemination (TAI) on 2 commercial dairy farms were blocked by parity (primiparous vs. multiparous) and were randomly assigned to receive 100 µg of GnRH versus 2,500 IU of hCG at G1. Overall, P/AI 39 d after TAI for cows inseminated with sexed dairy semen was greater for cows treated with GnRH than for cows treated with hCG within each parity (primiparous: 42.6% vs. 38.2%; multiparous: 39.4% vs. 30.3%). Similarly, P/AI 39 d after TAI for multiparous cows inseminated with conventional beef semen tended to be greater for cows treated with GnRH than for cows treated with hCG (41.1% vs. 34.3%). In experiment 2, lactating Holstein cows (n = 43) were blocked by parity and were randomly assigned to the treatment protocols described for experiment 1. Ovaries were evaluated with transrectal ultrasonography immediately before treatment and 24, 28, 32, 36, and 40 h after treatment to assess time from treatment to ovulation, and blood samples were collected immediately before G1, at the first PGF_2α treatment, 8 and 16 h later, at the second PGF_2α treatment, 8 and 16 h later, at the second GnRH (G2) treatment, and at TAI to compare luteolysis based on serum progesterone (P4) concentrations. Although mean (± standard error of the mean) time from treatment to ovulation was approximately 2 h greater for cows treated with hCG than for cows treated with GnRH (33.7 ± 0.6 vs. 31.5 ± 0.6 h), P4 concentrations during luteolysis and the proportion of cows with complete luteolysis (P4 <0.4 ng/mL at G2) did not differ between treatments. We conclude that replacing 100 µg of GnRH with 2,500 IU of hCG at G1 of a DO protocol decreased fertility to TAI in lactating dairy cows but did not affect the rate or completeness of luteolysis despite the increased interval from treatment to ovulation.