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 insemination conception rates using intravaginal progesterone, gonadotropin-releasing hormone, and prostaglandin F2alpha1.

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.

Evaluation of vaginal electrical resistance as an indicator of follicular maturity and suitability for timed artificial insemination in beef cows subjected to a synchronization of ovulation protocol.

Objectives were to test the hypothesis that vaginal electrical resistance (VER) could be used to identify cows without a large (<10mm) follicle at timed-AI (TAI) following a synchronization of ovulation protocol and thus serve as a prospective decision aid for determining cows that should not be inseminated. Brahman x Hereford (F1) females (n=233) were synchronized with the CO-Synch+CIDR protocol that consisted of a controlled internal drug release (CIDR) insert and i.m. injection of GnRH (GnRH-1; 100 microg) on day 0, removal of CIDR and i.m. injection of prostaglandin F2alpha (PGF; 25mg) on day 7, and i.m. injection of GnRH (GnRH-2, 100 microg) and TAI 66h after CIDR removal (day 10). Vaginal electrical resistance was determined with a commercially available device (Ovascan; Animark Inc., Aurora, CO) at days 0, 7, and 10. Transrectal ultrasonography was used on day 10 to assess ovarian morphology at TAI in all cattle and in a subset of females (n=98) on days 0 and 7. Mean (+/-S.E.M.) age, body condition score (BCS), BW and days postpartum were 7.2+/-0.3 years, 5.2+/-0.1, 538+/-5.3kg, and 77+/-1.1 days, respectively. Mean VER (Omega) was greatest (101.4+/-0.8) on day 0 and declined (P<0.01) to 95.2+/-0.8 and 82.0+/-0.8 Omega, respectively, on days 7 and 10. Mean diameter of the largest follicle and VER values in females conceiving after TAI differed (P=0.05) from those that did not conceive. Mean VER on days 7 and 10 and VER difference (VER on day 10 minus VER on day 7) did not differ between females with a small (<10mm) or large (>or=10mm) follicle at TAI. Timed-AI pregnancy rate was greater (P<0.01) for females with large follicles (43%) than those with small follicles (22%). Vaginal electrical resistance difference values, categorized as negative (<0 Omega) or neutral/positive (>or=0 Omega), did not differ between females that conceived to TAI compared with those that did not. We conclude that VER measurements, as used in the present study, are not adequately sensitive to differentiate between females with and without a large follicle and thus are unable to serve as a prospective decision aid for determining suitability for TAI after synchronization.

High-pressure steam sterilization of previously used CIDR inserts enhances the magnitude of the acute increase in circulating progesterone after insertion in cows.

Objectives were to compare serum concentrations of progesterone (P4) in ovariectomized cows receiving (1) new, (2) re-used disinfected (DIS), and (3) re-used autoclaved (AC) controlled internal drug release (CIDR) inserts. Five ovariectomized (OVX) beef cows were used in a replicated 3 x 3 Latin square design. Each experimental period was 7 days, with at least 48 h between periods. All re-used CIDR had been inserted previously in beef cows for 7 days. Upon removal, CIDR used for the DIS treatment were washed thoroughly and soaked in a chlorhexidine gluconate solution (0.03%) for 2h, rinsed thoroughly with water and air-dried. For the AC treatment, CIDR were not soaked in disinfectant but were steam sterilized at 121 degrees C and 724 mmHg for 20 min before use. Blood samples were collected at 0, 10, 30, 60, 180, and 480 min relative to time of insertion of CIDR, daily until day 7, and at 30, 60, and 180 min relative to time of removal for radioimmunoassay of P4. Mean serum concentrations (ng/mL) of P4 during the 7-day period of insertion were greater (P<0.03) for new (3.7+/-0.2) and AC (3.4+/-0.3) than for DIS CIDR (2.8+/-0.2). These effects were created primarily by differences occurring during the first 8h after CIDR insertion. Within this interval, mean concentrations (ng/mL) differed (P<0.05) among all groups, but values for AC (6.0+/-0.7) exceeded both new (4.6+/-0.5) and DIS (2.7+/-0.3) markedly. Autoclaving may be the best option when re-using CIDR inserts because it creates greater concentrations of P4 immediately after insertion and reduces maximally the risk of disease transmission.

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.