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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]

Objective was to compare serum concentrations of progesterone (P4) in ovariectomized cows receiving new, re-used disinfected, and re-used autoclaved Eazy-Breed CIDR inserts (Pfizer Animal Health, New York, NY). Five ovariectomized (OVX) Brahman × Hereford (F1) cows and one OVX Hereford cow were used in a replicated 3 × 3 Latin square design. Mean (± SEM) age and BW were 7.8 ± 0.9 yr and 604 ± 9 kg, respectively. Each experimental period was 7 d, with at least 48 h between periods. Treatments were 1) New, 2) Re-used disinfected (DIS), and 3) Re-used autoclaved (AC). All re-used CIDRs had been inserted previously in beef cows for 7 d. Upon removal, DIS CIDRs were washed thoroughly and soaked in a chlorhexidine gluconate solution (0.03%) for 2 h, rinsed thoroughly with water and air-dried. For the AC treatment, CIDRs were not soaked in disinfectant but were autoclaved at 121°C and 724 mm Hg for 20 min before use. Blood samples were collected at 0, 10, 30, 60, 180, and 480 min relative to time of insertion of CIDRs, daily until d 7, and at 30, 60, and 180 min relative to time of removal for RIA of P4. Mean serum concentrations (ng/mL) of P4 during the 7-d period of insertion were greater (P < 0.03) for New (3.7 ± 0.2) and AC (3.4 ± 0.3) than for DIS CIDRs (2.8 ± 0.2). These effects were created primarily by differences occurring during the first 8 h after CIDR insertion. Within this interval, mean concentrations differed (P < 0.05) between all treatments (New, 4.6 ± 0.5; DIS, 2.7 ± 0.3; AC, 6.0 ± 0.7). The majority (61 %) of maximum peak values occurred between 10 and 180 min after insertion. Mean concentrations during this period (New, 4.6 ± 0.5; DIS, 2.8 ± 0.3; AC, 5.8 ± 0.7) also differed (P < 0.01) between all treatments. 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. [ABSTRACT FROM AUTHOR]

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.

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.