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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 (F1) 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 receivecl 100 μg 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 PGF2α (PGF) on d 7, and i.m. injection of GnRH (CnRH–2) and timed AT (TAT) 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 (F1) 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 CnRH–2, and did not improve TAI pregnancy rates. [ABSTRACT FROM AUTHOR]

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 M (TM) 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 PGF2α (PGF) on d 7, and injection of GnRH (GnRH-2) and TM 48 h later. For Exp. 1, predominantly Brahman × Hereford (F1) and Brangns 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 ofobservations 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 × 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 × 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. [ABSTRACT FROM AUTHOR]

Objectives were to evaluate the effect of presynchronization with GnRH on conception rates (CR, Exp.1) and ovarian events (Exp.2) in Bos indicus-influenced females synchronized with the CO-Synch + CIDR (CSC) protocol. In Exp.1, 135 Brahman x Hereford (F1) females were stratified by BW, BCS, age, and d postpartum (dpp) and assigned randomly to 1) Presynch; presynchronization followed by CSC or 2) CSC only. On d -7, cattle received either 100 μg GnRH (GnRHpre) or 2 mL saline i.m. The CSC protocol included an Eazy-Breed CIDR and i.m. injection of GnRH (GnRH-1) on d 0, removal of CIDR and i.m. injection of 25 mg PGF2α on d 7, and i.m. injection of GnRH (GnRH-2) and timed AI (TAI) 66 h after CIDR removal (d 10). Mean (± SEM) age, BCS, BW and dpp were 6.1 ± 0.4 yr, 5.4 ± 0.1, 498 ± 8.7 kg, and 77 ± 1.8 d, respectively. Conception rates for Presynch (37 ± 6 %) and CSC (49 ± 6.1 %) did not differ. Deleting data from females with BCS < 5 (n = 18) increased TAI conception rates to 38 ± 6.3 % and 54 ± 6.7 %, respectively (Presynch vs CSC; P = 0.085). In Exp.2, non-cycling (46 %) and cycling (54 %) Brahman x Hereford (F1) cows (n = 98) were stratified as described previously and assigned randomly to Presynch or CSC. Ultrasonography and serum progesterone were utilized to monitor ovarian events. Mean age, BCS, BW and dpp were similar to Exp. 1. Ovulatory response and synchronized follicular wave emergence (SFWE) after GnRHpre were 50 ± 7.1 % and 84 ± 5.2 %, respectively. Ovulatory responses after GnRH-1 differed (P < 0.01) between Presynch (58 ± 7.1 %) and CSC (27 ± 6.5 %) but treatment did not affect SFWE after GnRH-1 (86 ± 3.6 %), ovulation after GnRH-2 (74 ± 4.4%), follicular size, or TAI CR (31 ± 4.7 %). Presynch improved ovulation rate after GnRH-1, but did not increase CR compared to CSC. [ABSTRACT FROM AUTHOR]

Objectives were to use retrospective analysis to determine the efficacy of VER for identifying cows with and without a mature preovulatory follicle (defined as ≥ 10 mm) at timed AI (TAI) and as a prospective decision aid for determining cows that should not be bred. Brahman x Hereford (F1) females (n=233) were synchronized with the CO-Synch + CIDR protocol that consisted of an Eazy-Breed CIDR and i.m. injection of GnRH (GnRH-1; 100 μg) on d 0, removal of CIDR and i.m. injection of Prostaglandin F2α (PGF; 25 mg) on d 7, and i.m. injection of GnRH (GnRH-2, 100 μg) and TAI 66 h after CIDR removal (d 10). A commercially-available device (Ovascan; Animark Inc., Aurora, CO) was used to determine VER at d 0, 7, and 10. Transrectal ultrasonography was used on d 10 to assess ovarian morphology at TAI in all cattle and in a subset of females (n=98) on d 0 and 7. Mean (± SEM) age, BCS, BW and d postpartum were 7.2 ± 0.3 yr, 5.2 ± 0.1, 538 ± 5.3 kg, and 77 ± 1.1 d, respectively. Mean VER (ohms) was greatest (101.8 ± 1.1) on d 0 and declined (P < 0.01) to 95 ± 0.7 and 82.4 ± 0.7 ohms, respectively, on d 7 and 10. We observed a low negative relationship (r = - 0.35; P < 0.001) between follicular size and VER on d 0, 7, and 10. Timed AI conception rate was correlated positively (r = 0.16; P < 0.05) with follicular size and negatively (r = - 0.15; P < 0.05) with VER at TAI. Timed AI conception rate was also correlated with changes in follicular size (FollSizediff; r = 0.24; P < 0.05) and VER (VERdiff; r = - 0.18; P < 0.01) between d 10 and 7. However, VERdiff and FollSizediff were not correlated. Vaginal electrical resistance at TAI and VERdiff did not differ between females that became pregnant and those that did not. Females without a large follicle on d 10 were not identifiable with VER. [ABSTRACT FROM AUTHOR]