Presynchronization with gonadotropin-releasing hormone increases the proportion of Bos indicus-influenced females ovulating at initiation of synchronization but fails to improve synchronized new follicular wave emergence or fixed-time artificial inseminat

The objectives were to evaluate the effect of presynchronization with GnRH on pregnancy rates (Exp. 1) and ovarian events (Exp. 2) in Bos indicus-influenced females synchronized with CO-Synch + controlled internal drug release (CIDR) as described below. In Exp. 1, a total of 135 Brahman x Hereford (F(1)) females were assigned randomly after stratification to 1) Presynch; presynchronization followed by CO-Synch + CIDR, or 2) No Presynch; CO-Synch + CIDR without presynchronization. On d -7, cattle received 100 microg of GnRH or 2 mL of intramuscular (i.m.) saline. On d 0, all cattle received a CIDR and i.m. injection of GnRH (GnRH-1), followed by CIDR removal and i.m. injection of 25 mg of PGF(2alpha) (PGF) on d 7, and i.m. injection of GnRH (GnRH-2) and timed AI (TAI) 66 h after CIDR removal (d 10). An additional 77 cows not involved in the Presynch comparison were also treated with CO-Synch + CIDR. Pregnancy rates for Presynch (37.3 +/- 6%) and No Presynch (48.5 +/- 6.1%) did not differ (P = 0.6). Pregnancy rate for all CO-Synch + CIDR-treated cattle combined was 41.9 +/- 6.1 (n = 145). In Exp. 2, we examined ovarian events in 98 Brahman x Hereford (F(1)) cows assigned randomly to Presynch or No Presynch. Ovulatory response to GnRH-1 was greater (P < 0.01) in the Presynch (58 +/- 7.1%) than in the No Presynch (27.1 +/- 6.5%) group. However, emergence of a synchronized new follicular wave after GnRH-1 and ovulation rate after GnRH-2 did not differ between groups (P = 0.4). Presynchronization increased the proportion of females ovulating after GnRH-1, but this did not increase synchrony of new follicular wave emergence or ovulation after GnRH-2, and did not improve TAI pregnancy rates.

Zuluaga JF ，Saldarriaga JP ，Cooper DA ，Cartmill JA ，Williams GL ... -  《-》

Ovarian, hormonal, and reproductive events associated with synchronization of ovulation and timed appointment breeding of Bos indicus-influenced cattle using intravaginal progesterone, gonadotropin-releasing hormone, and prostaglandin F2alpha.

The objectives of this study were to 1) compare cumulative pregnancy rates in a traditional management (TM) scheme with those using a synchronization of ovulation protocol (CO-Synch + CIDR) for timed AI (TAI) in Bos indicus-influenced cattle; 2) evaluate ovarian and hormonal events associated with CO-Synch + CIDR and CO-Synch without CIDR; and 3) determine estrual and ovulatory distributions in cattle synchronized with Select-Synch + CIDR. The CO-Synch + CIDR regimen included insertion of a controlled internal drug-releasing device (CIDR) and an injection of GnRH (GnRH-1) on d 0, removal of the CIDR and injection of PGF2alpha (PGF) on d 7, and injection of GnRH (GnRH-2) and TAI 48 h later. For Exp. 1, predominantly Brahman x Hereford (F1) and Brangus females (n = 335) were stratified by BCS, parity, and day postpartum (parous females) before random assignment to CO-Synch + CIDR or TM. To maximize the number of observations related to TAI conception rate (n = 266), an additional 96 females in which TM controls were not available for comparison also received CO-Synch + CIDR. Conception rates to TAI averaged 39 +/- 3% and were not affected by location, year, parity, AI sire, or AI technician. Cumulative pregnancy rates were greater (P < 0.05) at 30 and 60 d of the breeding season in CO-Synch + CIDR (74.1 and 95.9%) compared with TM (61.8 and 89.7%). In Exp. 2, postpartum Brahman x Hereford (F1) cows (n = 100) were stratified as in Exp. 1 and divided into 4 replicates of 25. Within each replicate, approximately one-half (12 to 13) received CO-Synch + CIDR, and the other half received CO-Synch only (no CIDR). No differences were observed between treatments, and the data were pooled. Percentages of cows ovulating to GnRH-1, developing a synchronized follicular wave, exhibiting luteal regression to PGF, and ovulating to GnRH-2 were 40 +/- 5, 60 +/- 5, 93 +/- 2, and 72 +/- 4%, respectively. In Exp. 3, primiparous Brahman x Hereford, (F1) heifers (n = 32) and pluriparous cows (n = 18) received the Select Synch + CIDR synchronization regimen (no GnRH-2 or TAI). Mean intervals from CIDR removal to estrus and ovulation, and from estrus to ovulation were 70 +/- 2.9, 99 +/- 2.8, and 29 +/- 2.2 h, respectively. These results indicate that the relatively low TAI conception rate observed with CO-Synch + CIDR in these studies was attributable primarily to failure of 40% of the cattle to develop a synchronized follicular wave after GnRH-1 and also to inappropriate timing of TAI/GnRH-2.

Saldarriaga JP ，Cooper DA ，Cartmill JA ，Zuluaga JF ，Stanko RL ，Williams GL ... -  《-》

Strategies to improve fertility in postpartum multiparous Bos indicus cows submitted to a fixed-time insemination protocol with gonadotropin-releasing hormone and prostaglandin F2alpha.

In Exp. 1, we evaluated the effects of 2 lengths of progesterone exposure [CIDR (controlled intravaginal drug release); 7 vs. 14 d] before a modified CO-Synch protocol [50.0-microg injection of GnRH 6.5 d before a 25.0-mg injection of PGF(2alpha) followed by another injection of GnRH and fixed-time AI (TAI) 2 d after PGF(2alpha)], with or without temporary weaning (TW) before GnRH treatments, on fertility of suckled multiparous Bos indicus cows (n = 283) and on calf performance. Timed AI pregnancy rates for cows receiving 7 d CIDR + TW, 7 d CIDR, 14 d CIDR + TW, and 14 d CIDR were 53, 47, 46, and 41%, respectively (P > 0.10). Calves submitted to two 48-h TW 6 d apart had decreased mean BW at 240 d (187.9 +/- 2.7 vs. 195.5 +/- 2.7 kg; P < 0.05), but BW at 420 d was not affected by TW (240.1 +/- 5.1 kg). In Exp. 2, we evaluated the effect of no treatment and treatment with or without a CIDR insert between GnRH and PGF(2alpha) treatments of a modified CO-Synch protocol on pregnancy rate to TAI, and throughout a 90-d breeding season in suckled multiparous Bos indicus cows (n = 453). The inclusion of a CIDR between first GnRH and PGF(2alpha) treatments of a modified CO-Synch protocol did not improve pregnancy rate (29 and 33% for cows receiving CO-Synch + CIDR and CO-Synch protocol, respectively), and cycling cows had poorer TAI pregnancy rates than anestrous cows treated with either synchronization protocol (21.7 vs. 40.7%; P < 0.05). However, regardless of treatment with CIDR, cows submitted to TAI protocol had greater (P < 0.05) pregnancy rates at 30 (54.8 vs. 11.2%), 60 (72.1 vs. 38.8%), and 90 d (82.0 vs. 57.9%) of breeding season than untreated cows.

Sá Filho OG ，Vilela ER ，Geary TW ，Vasconcelos JL ... -  《-》

Comparison of progestin-based protocols to synchronize estrus and ovulation before fixed-time artificial insemination in postpartum beef cows.

This experiment was designed to compare pregnancy rates in postpartum beef cows resulting from fixed-time AI (FTAI) after treatment with 1 of 2 protocols to synchronize estrus and ovulation. Cross-bred, suckled beef cows (n = 650) at 4 locations (n = 210; n = 158; n = 88; and n = 194) were assigned within a location to 1 of 2 protocols within age group by days postpartum and BCS. Cows assigned to the melengestrol acetate (MGA) Select treatment (MGA Select; n = 327) were fed MGA (0.5 mg x head(-1) x d(-1)) for 14 d, GnRH (100 microg of Cystorelin i.m.) was injected on d 26, and prostaglandin F2alpha (PG; 25 mg of Lutalyse i.m.) was injected on d 33. Cows assigned to the CO-Synch + controlled internal drug release (CIDR) protocol (CO-Synch + CIDR; n = 323) were fed a carrier for 14 d, were injected with GnRH and equipped with an EAZI-BREED CIDR insert (1.38 g of progesterone, Pfizer Animal Health, New York, NY) 12 d after carrier removal, and PG (25 mg of Lutalyse i.m.) was injected and the CIDR were removed on d 33. Fixed-time AI was performed at 72 or 66 h after PG for the MGA Select or CO-Synch + CIDR groups, respectively. All cows were injected with GnRH (100 microg of Cystorelin i.m.) at the time of insemination. Blood samples were collected 8 and 1 d before the beginning of MGA or carrier to determine estrous cyclicity status of the cows (estrous cycling vs. anestrus) before treatment [progesterone > or = 0.5 ng/mL (MGA Select, 185/327, 57%; CO-Synch + CIDR, 177/323, 55%); P = 0.65]. There was no difference (P = 0.20) in pregnancy rate to FTAI between treatments (MGA Select, 201/327, 61%; CO-Synch + CIDR, 214/323, 66%). There was also no difference (P = 0.25) between treatments in final pregnancy rate at the end of the breeding period (MGA Select, 305/327, 93%; CO-Synch + CIDR, 308/323, 95%). These data indicate that pregnancy rates to FTAI were comparable after administration of the MGA Select or CO-Synch + CIDR protocols. Both protocols provide opportunities for beef producers to utilize AI and potentially eliminate the need to detect estrus.

Schafer DJ ，Bader JF ，Meyer JP ，Haden JK ，Ellersieck MR ，Lucy MC ，Smith MF ，Patterson DJ ... -  《-》

Evaluation of human chorionic gonadotropin as a replacement for gonadotropin-releasing hormone in ovulation-synchronization protocols before fixed timed artificial insemination in beef cattle.

Two experiments were conducted during 2 yr to evaluate differences in ovulation potential and fertility in response to GnRH or hCG. In Exp. 1, 46 beef cows were given 100 microg of GnRH or 500, 1,000, 2,000, or 3,000 IU of hCG. Ovulation incidence was not different between GnRH and any of the hCG doses, indicating that ovulatory capacity of at least 500 IU of hCG was equivalent to GnRH. In Exp. 2, beef cows (n = 676) at 6 locations were assigned randomly to a 2 x 3 factorial arrangement of treatments. Main effects were: 1) pre-timed AI (TAI) treatment (GnRH or hCG) and 2) post-TAI treatment (saline, GnRH, or hCG) to initiate resynchronization of ovulation in previously inseminated cattle. Blood samples were collected (d -21 and -10) to determine progesterone concentrations and assess cyclicity. Cattle were treated with a progesterone insert on d -10 and with 100 microg of GnRH or 1,000 IU of hCG. A PGF(2alpha) injection was given at insert removal on d -3. Cows were inseminated 62 h (d 0) after insert removal. On d 26 after first TAI, cows of unknown pregnancy status were treated with saline, GnRH, or hCG to initiate a CO-Synch protocol. Pregnancy was diagnosed 33 d after first TAI to determine pregnancies per AI (P/AI). Nonpregnant cows at 6 locations in yr 1 and 1 location in yr 2 were given PGF(2alpha) and inseminated 56 h later, concurrent with a GnRH injection. Five weeks later, pregnancy diagnosis was conducted to determine pregnancy loss after first TAI and pregnancy outcome of the second TAI. Injection of pre-TAI hCG reduced (P < 0.001) P/AI compared with GnRH, with a greater reduction in cycling cows. Post-TAI treatments had no negative effect on P/AI resulting from the first TAI. Serum progesterone was greater (P = 0.06) 7 d after pre-TAI hCG than after GnRH and greater (P < 0.05) after post-TAI hCG on d 26 compared with saline 7 d after treatment in association with greater frequency of multiple corpora lutea. Compared with saline, injections of post-TAI GnRH and hCG did not increase second insemination P/AI, and inconsistent results were detected among locations. Use of hCG in lieu of GnRH is contraindicated in a CO-Synch + progesterone insert protocol. Compared with a breeding season having only 1 TAI and longer exposure to cleanup bulls, total breeding season pregnancy rate was reduced by one-third, subsequent calving distribution was altered, and 50% more AI-sired calves were obtained by applying 2 TAI during the breeding season.

Burns MG ，Buttrey BS ，Dobbins CA ，Martel CA ，Olson KC ，Lamb GC ，Stevenson JS ... -  《-》