Effect of gonadotropin-releasing hormone or prostaglandin F(2α)-based estrus synchronization programs for first or subsequent artificial insemination in lactating dairy cows.

The objective was to evaluate the effects of GnRH or PGF(2α)-based synchronization and resynchronization programs on fertility in lactating dairy cows. For experiment 1, cows (n=1,521) were presynchronized with 2 injections of PGF given at 36 and 50 DIM and assigned to 1 of 3 protocols: Ovsynch [OVS; n=552; GnRH injection, PGF(2α) injection 7 d later, GnRH injection 56 h later, and timed artificial insemination (TAI) 16 h later] beginning at 14 d after presynchronization (PS), GnRH-GnRH-PGF(2α)-GnRH (GGPG; n=402) treatment with a GnRH injection given 7 d after PS and OVS 7 d later, or PGF(2α)-GnRH-PGF(2α)-GnRH (P7GPG; n=567) treatment with a PGF(2α) injection given 7 d after PS and OVS beginning 7 d later. Experiment 2 cows (n=2,327) were assigned to 1 of 3 resynchronization protocols 7 d before nonpregnancy diagnosis (NPD): GGPG cows (n=458) received a GnRH injection at enrollment and OVS at NPD; P7GPG cows (n=940) received a PGF(2α) injection at NPD and OVS 7 d later; and P11GPG cows (n=929) received a PGF(2α) injection 3 d after NPD and OVS 11 d later. In both experiments, cows were artificially inseminated upon estrus detection (ED). In experiment 1, 52.3% of cows were artificially inseminated upon ED, with GGPG having reduced ED (GGPG=46.8 vs. OVS=50.7 and P7GPG=57.7%). Treatments did not affect overall pregnancy per artificial insemination (P/AI) at 36 and 66 d after AI (OVS=34.1 and 32.3, P7GPG=34.6 and 31.9, and GGPG=31.3 and 28.1%, respectively) or pregnancy loss but cows artificially inseminated upon ED had higher P/AI than cows undergoing TAI (ED cows=37.9 vs. TAI cows=28.8%). Treatment did not affect P/AI for cows artificially inseminated upon ED or TAI at 36 and 66 d after AI (OVS=34.1 and 32.3, P7GPG=34.6 and 31.9, and GGPG=31.3 and 28.1%). Median days in milk at first AI was affected by treatment (P7GPG=59 vs. OVS=68 and GGPG=68 d). In experiment 2, GGPG reduced ED (GGPG=23.3 vs. P7GPG=74.9 and P11GPG=79.6%). Treatment did not affect overall P/AI at 36 and 66 d after AI (GGPG=29.2 and 25.8, P7GPG=28.7 and 26.6, and P11GPG=31.9 and 30.2%) or pregnancy loss. Cows artificially inseminated upon ED had greater P/AI than TAI cows (ED=32.3 and TAI=25.1%). However, treatment did not affect P/AI for cows artificially inseminated upon ED at 36 and 66 d after AI (GGPG=29.6 and 27.3, P7GPG=29.4 and 28.1, and P11GPG=35.7 and 33.7%) or TAI (GGPG=29.1 and 25.3, P7GPG=25.0 and 22.1, and P11GPG=16.9 and 16.9%). Median days between NPD and AI was affected by treatment (GGPG=10 vs. P7GPG=4 and P11GPG=7 d). Prostaglandin-based programs increased ED and reduced interval to first AI and between AI. Gonadotropin-releasing hormone-based programs increased the proportion of TAI cows. Cows artificially inseminated upon ED had increased P/AI compared with TAI cows.

Bruno RG ，Farias AM ，Hernández-Rivera JA ，Navarrette AE ，Hawkins DE ，Bilby TR ... -  《-》

Evaluation of presynchronized resynchronization protocols for lactating dairy cows.

The objectives of this experiment were to determine the speed at which cows that had their estrous cycle presynchronized with a GnRH or PGF(2α) injection are reinseminated and become pregnant. Furthermore, this experiment aimed to determine whether treatment with a controlled internal drug-releasing (CIDR) insert during the timed artificial insemination (AI) protocol improves pregnancy per AI (P/AI) of cows that had their estrous cycle presynchronized with GnRH or PGF(2α). Lactating cows from 2 herds were assigned to 1 of 2 presynchronization treatments at 32 ± 4 d after AI: GGPG (n=452)--GnRH injection at enrollment (d 0), 7d before the start of the timed AI protocol, and P11GPG (n=466)--PGF(2α) injection on d 3, 11 d before the start of the timed AI protocol. Cows observed in estrus at any interval after enrollment were reinseminated on the same day. Cows not observed in estrus by d 7 were paired by presynchronization treatment and assigned to receive or not receive a CIDR insert during the timed AI protocol (CIDR = 240, no CIDR = 317). Timed AI protocols were the Ovsynch56 at site A and the Cosynch48 at site B. A subsample of cows from site A had their ovaries scanned by ultrasound at enrollment and on the day of the first GnRH and PGF(2α) injections of the timed AI protocol and had blood sampled at each injection of the timed AI protocol for determination of progesterone concentration. Cows were examined for pregnancy 32 ± 4 and 67 ± 4 d after reinsemination. Cows in the P11GPG treatment had a faster reinsemination rate [adjusted hazard ratio = 1.24 (95% CI = 1.07, 1.45)] and were less likely to be submitted to the timed AI protocol (40.3 vs. 89.8%) and to be reinseminated at a fixed time (38.6 vs. 83.9%). The interval from enrollment to reinsemination was shorter for cows in the P11GPG group (13.0 ± 0.4 vs. 15.0 ± 0.2d). Presynchronization treatment did not affect P/AI 32 ± 4 d (GGPG = 42.3%, P11GPG = 39.3%) and 67 ± 4 d (GGPG = 37.0%, P11GPG = 35.4%) after reinsemination. Pregnancy rate from d 0 to 7 (GGPG = 3.6%, P11GPG = 17.7%) and from d 8 to 14 (GGPG = 1.6%, P11GPG = 5.7%) were greater for cows in the P11GPG treatment. Treatment with the CIDR insert during the timed AI protocol did not affect P/AI 32 ± 4 d (CIDR = 41.7%, no CIDR = 41.4%) and 67 ± 4 d (CIDR = 36.5%, no CIDR = 35.3%) after reinsemination. A greater percentage of cows in the GGPG treatment had progesterone concentration ≥ 1 ng/mL on the day of the first GnRH injection of the timed AI protocol (83.8 vs. 51.5%), but a greater percentage of cows in the P11GPG treatment ovulated in response to the first GnRH injection of the timed AI protocol (66.1 vs. 46.8%). We conclude that the P/AI of cows that had their estrous cycle presynchronized with GnRH or PGF(2α) was not different, but in herds with adequate estrous detection efficiency and accuracy, presynchronization with PGF(2α) may reduce the interval to the establishment of pregnancy.

Chebel RC ，Scanavez AA ，Silva PR ，Moraes JG ，Mendonça LG ，Lopes G Jr ... -  《-》

Effect of an Ovsynch56 protocol initiated at different intervals after insemination with or without a presynchronizing injection of gonadotropin-releasing hormone on fertility in lactating dairy 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.

Bruno RG ，Moraes JG ，Hernández-Rivera JA ，Lager KJ ，Silva PR ，Scanavez AL ，Mendonça LG ，Chebel RC ，Bilby TR ... -  《-》

Effect of presynchronization with human chorionic gonadotropin or gonadotropin-releasing hormone 7 days before resynchronization of ovulation on fertility in lactating dairy cows.

Our objectives were to (1) compare the effect on pregnancies per artificial insemination (P/AI) of presynchronization of the estrous cycle with human chorionic gonadotropin (hCG) 7d before resynchronization of ovulation (Resynch) initiated 25 d after timed artificial insemination (TAI) and compare the presynchronization treatment with the Double-Ovsynch (DO) protocol, and (2) evaluate whether hCG for presynchronization could be replaced with GnRH. In experiment 1, lactating Holstein cows were blocked by parity and were randomly assigned to receive (1) Resynch-25 (D25), the Resynch protocol (GnRH-7 d-PGF(2 α)-56 h-GnRH-16 h-TAI) initiated 25 d after TAI (n=418); (2) HGPG, presynchronization with hCG (2,000 IU of Chorulon) 7d before D25 (n=450); and (3) DO (Pre-Resynch, GnRH-7 d-PGF(2 α)-72 h-GnRH; Breeding-Resynch, GnRH-7 d-PGF(2 α)-56 h-GnRH-16 h-TAI) initiated 22d after TAI (n=405). At 29 d after TAI, cows in the HGPG (37.3%) and DO (35.8%) groups had more P/AI than did cows in the D25 group (28.0%), and cows in the HGPG and DO groups continued to have more P/AI than did cows in the D25 group at 53 d after TAI. Presynchronization with hCG induced ovulation in 76% of the cows, which increased the percentage of HGPG cows with a corpus luteum at the initiation of Resynch compared with cows in the D25 group. In experiment 2, the D25 (n=368) and HGPG (n=338) treatments described in experiment 1 were compared in addition to a third treatment (GGPG; n=351), in which the hCG injection 18 d after TAI was replaced with a GnRH injection (200 µg of gonadorelin). At 32 d after TAI, cows in the HGPG group had more P/AI than did cows in the D25 group (33.7 vs. 25.5%), whereas cows in the GGPG group had intermediate P/AI (31.6%). At 53 d after TAI, P/AI tended to be greater for cows in the HGPG group than for those in the D25 group, whereas P/AI for cows in the GGPG group did not differ from that for cows in the D25 group. Treatment with hCG and GnRH 18d after TAI induced ovulation in 58.8 and 48.2% of cows, respectively, but did not increase the percentage of cows with a corpus luteum at the initiation of Resynch. More cows in the HGPG and GGPG groups had their estrous cycles synchronized after the resynchronization protocols compared with cows in the D25 group. We conclude that presynchronization with hCG increased fertility by increasing synchronization to the Resynch protocol, whereas presynchronization with GnRH improved synchronization to the Resynch protocol but did not improve fertility when compared with no presynchronization or presynchronization with hCG.

Giordano JO ，Wiltbank MC ，Guenther JN ，Ares MS ，Lopes G Jr ，Herlihy MM ，Fricke PM ... -  《-》

Effect of presynchronization strategy before Ovsynch on fertility at first service in lactating dairy cows.

The aim of this study was to evaluate the effect of presynchronization with or without the detection of estrus on first service pregnancy per artificial insemination (P/AI) and on Ovsynch outcome in lactating dairy cows. A total of 511 cows were divided randomly but unevenly into 3 treatment groups at 44 to 50 days in milk (DIM). Ovsynch was started at the same time (69 to 75 DIM) in all three groups. Cows in the Ovsynch group (CON, N = 126) received no presynchronization before Ovsynch, and all cows were bred by timed AI (TAI). Cows in the presynchronization with estrus detection (PED) and the presynchronization with only TAI (PTAI) groups received two doses of prostaglandin F(2α) (PGF) 14 days apart, starting at 44 to 50 DIM. Ovsynch was initiated 11 days after the second PGF treatment. Cows in the PED group (N = 267) received AI if estrus was detected after either PGF injection. Cows that were not determined to be in estrus after PGF injection received Ovsynch and TAI. Cows in the PTAI group (N = 118) were not inseminated to estrus, with all cows receiving TAI after Ovsynch. The ovulatory response to the first GnRH injection administered as part of Ovsynch differed (P = 0.002) among treatment groups (83.1% in PTAI, 72.6% in PED, and 62.7% in CON). However, the ovulatory response to the second injection of GnRH during Ovsynch did not differ among treatment groups. Of the 267 PED cows, a total of 132 (49.4%) exhibited estrus and were inseminated. The P/AI at the 31-day pregnancy diagnosis was similar between the cows in the PED group with AI after estrus detection (37.9%; 50/132) and those bred with TAI (34.1%; 46/135). The P/AI in the CON group (46.8%; 59/126) was greater (P < 0.05) than that in the PED group (36.0%; 96/267). In addition, the P/AI in the CON group was greater (P = 0.04) than that in the PED cows receiving TAI (34.1%; 46/135) but less than that in the PED cows bred to estrus (37.9%; 50/132) (P = 0.16). At the 31-day pregnancy diagnosis, the cows in the PTAI group had greater P/AI (55.9%; 66/118) than both those in the PED group (P < 0.01; either estrus or TAI) and those in the CON group (P = 0.08). Thus, presynchronization with PGF (PTAI) increased the ovulatory response to Ovsynch and improved P/AI in dairy cows. Interestingly, the breeding of cows to estrus during presynchronization reduced fertility to the TAI and overall fertility, including cows bred to estrus and TAI. These results indicate that maximal fertility is obtained when all cows receive TAI after the presynchronization protocol.

Gumen A ，Keskin A ，Yilmazbas-Mecitoglu G ，Karakaya E ，Alkan A ，Okut H ，Wiltbank MC ... -  《-》