<p>A series of experiments were designed to study alternative estrus synchronization and resynchronization protocols to facilitate the use of artificial insemination in cattle. </p><p>Studies were conducted to study the effects of estradiol cypionate (ECP) on follicular dynamics, time of ovulation, and pregnancy rate to timed-AI (TAI) in CIDR-based protocols. Although administration of 1 mg ECP did not result in synchronous follicular wave emergence, a dose of 0.5 mg ECP synchronized LH release and ovulation. Administration of ECP 24 h after CIDR removal resulted in acceptable pregnancy rate. However, treatment with ECP at CIDR removal resulted in acceptable pregnancy rate only if follicular wave emergence was synchronized with estradiol-17â (E-17â). </p><p>The efficacy of two estradiol preparations (5 mg of E-17â or estadiol valerate; EV) and reduced doses of EV on CL and ovarian follicular dynamics and superovulatory response were examined. When doses of 5 mg were compared, EV treatment resulted in a more variable interval to follicular wave emergence and a lower superovulatory response than E-17â. However, EV at a dose of 1 or 2 mg was efficacious in synchronizing follicle wave emergence in CIDR-treated cattle.</p><p>Pregnancy rates were compared following TAI in cattle given a new or previously used CIDR and injections of estradiol, with or without progesterone, to synchronize follicular wave emergence. Pregnancy rate following TAI did not differ between cattle treated with a new or once-used CIDR, but pregnancy rate was lower in cattle treated with one or two twice-used CIDR. The addition of an injection of progesterone to the estradiol treatment at CIDR insertion did not enhance pregnancy rate. </p><p>The efficacy of progestins (used CIDR and MGA), and E-17â, ECP, GnRH, or progesterone treatment for resynchronization of estrus in cattle not pregnant following TAI were investigated. Progestin treatment resulted in the majority of nonpregnant heifers detected in estrus over a 4-d interval. Conception rates were higher in heifers resynchronized with a once-used CIDR than with MGA. GnRH at CIDR insertion synchronized follicular wave emergence in cows, but did not increase conception rate in heifers. E-17â at CIDR insertion (1.5 mg) and removal (0.5 mg) resulted in decreased pregnancy rate following TAI. In summary, protocols described in this thesis resulted in acceptable pregnancy rates following TAI and resynchronization of previously inseminated heifers with progestins resulted in variable estrus and pregnancy rates.</p>

<p>A series of experiments were designed to study alternative estrus synchronization and resynchronization protocols to facilitate the use of artificial insemination in cattle. </p><p>Studies were conducted to study the effects of estradiol cypionate (ECP) on follicular dynamics, time of ovulation, and pregnancy rate to timed-AI (TAI) in CIDR-based protocols. Although administration of 1 mg ECP did not result in synchronous follicular wave emergence, a dose of 0.5 mg ECP synchronized LH release and ovulation. Administration of ECP 24 h after CIDR removal resulted in acceptable pregnancy rate. However, treatment with ECP at CIDR removal resulted in acceptable pregnancy rate only if follicular wave emergence was synchronized with estradiol-17â (E-17â). </p><p>The efficacy of two estradiol preparations (5 mg of E-17â or estadiol valerate; EV) and reduced doses of EV on CL and ovarian follicular dynamics and superovulatory response were examined. When doses of 5 mg were compared, EV treatment resulted in a more variable interval to follicular wave emergence and a lower superovulatory response than E-17â. However, EV at a dose of 1 or 2 mg was efficacious in synchronizing follicle wave emergence in CIDR-treated cattle.</p><p>Pregnancy rates were compared following TAI in cattle given a new or previously used CIDR and injections of estradiol, with or without progesterone, to synchronize follicular wave emergence. Pregnancy rate following TAI did not differ between cattle treated with a new or once-used CIDR, but pregnancy rate was lower in cattle treated with one or two twice-used CIDR. The addition of an injection of progesterone to the estradiol treatment at CIDR insertion did not enhance pregnancy rate. </p><p>The efficacy of progestins (used CIDR and MGA), and E-17â, ECP, GnRH, or progesterone treatment for resynchronization of estrus in cattle not pregnant following TAI were investigated. Progestin treatment resulted in the majority of nonpregnant heifers detected in estrus over a 4-d interval. Conception rates were higher in heifers resynchronized with a once-used CIDR than with MGA. GnRH at CIDR insertion synchronized follicular wave emergence in cows, but did not increase conception rate in heifers. E-17â at CIDR insertion (1.5 mg) and removal (0.5 mg) resulted in decreased pregnancy rate following TAI. In summary, protocols described in this thesis resulted in acceptable pregnancy rates following TAI and resynchronization of previously inseminated heifers with progestins resulted in variable estrus and pregnancy rates.</p>

The objective of this study was to examine the effects of presynchronization and recombinant bovine somatotropin (rbST) on conception rates following a timed insemination (TAI) protocol in lactating dairy cows. A further objective included the evaluation of the efficacy of the Early Conception Factor (ECF) test kit. Recombinant bST may offer some benefit when used in conjunction with estrus synchronization and TAI. Presynchronization treatment consisted of two injections of PGF2α given 14 d apart, with the second dose administered 14 d prior to the initiation of a TAI protocol. A total of 216 lactating Holstein cows were presynchronized with PGF2α and then received GnRH (100μg) at 67 ± 7 d post partum (PP), administration of PGF2α (25 mg) 7 d later, another GnRH (100μg) administration 2 d after PGF2α, and were inseminated 8-18h later (OvSynch). First service conception rate (CR) was determined by rectal palpation at 42 ± 7 d after artificial insemination (AI). Treated cows (n=113) received rbST 67 ± 7 d PP whereas control cows (n = 113) were presynchronized without rbST. The cycling status of all cows was determined by paired milk P4 levels at 53 and 67 ± 7 d PP. No differences (P > 0.10) in conception rate were observed between control and rbST treated cows (44.7 and 40.7% respectively), nor was there any interaction of cyclicity and rbST. Milk samples were collected 7 d following AI for use in ECF test kit evaluation. Samples were stored at -20ºC (n=216) and at 5ºC (n=113) until assayed. Test results for frozen and refrigerated samples were compared to conception rates determined by rectal palpation at 42 ± 7 d after AI. The rate of false positive and negative results for frozen milk samples were 36.1 and 14.8% respectively, and 40.7 and 7.1% for refrigerated milk samples. Treatment with rbST at the time of the first GnRH injection of an OvSynch protocol did not significantly alter first service conception rates. Additionally, an acceptable 92.9% accuracy of the ECF test for the detection of open cows 7 d after AI using milk samples stored at 5ºC was obtained. / Master of Science

Objectives were to: 1) Evaluate the effectiveness of presynchronization with GnRH before the CO‐Synch + CIDR protocol with timed AI (TAI) at 66 h in Bos indicus‐influenced cattle; 2) Characterize ovarian events associated with the presynchronization; 3) Evaluate the efficacy of measuring vaginal electrical resistance (VER) to assess follicular maturity at TAI; and 4) Compare serum concentrations of progesterone (P4) in ovariectomized cows bearing new or previously used CIDR devices with or without autoclaving. In Exp. 1 and 2, cattle received either GnRH or saline on day ‐7. The CO‐Synch + CIDR protocol included a CIDR insert and GnRH (GnRH‐1; day 0), removal of CIDR and PGF2α on day 7, and GnRH (GnRH‐2) and TAI 66 h after CIDR removal. In Exp. 1, pregnancy rate of females with BCS ≥ 5 tended to differ (P=0.085) between Presynch (38%) and CO‐Synch + CIDR (54%). In Exp. 2, ovulatory response to GnRH‐1 was greater (P<0.01) in the Presynchronization (58%) than in the CO‐Synch + CIDR (27.1%) group. Emergence of a follicular wave after GnRH‐1 and ovulation rate after GnRH‐2 did not differ between groups. More (P<0.01) females that developed a follicular wave after GnRH‐1 ovulated (82%) after GnRH‐2, compared to those that did not (29%). Mean VER (ohms) was greatest (101.4±0.8) on day 0 and declined (P<0.01) to 95.2±0.8 and 82±0.8, respectively, on days 7 and 10. We observed a low negative but significant relationship (r=0.38; P<0.001) between VER and follicular size on day 0, 7, and 10. VER difference (day 10 minus day 7) did not differ between females with small and large follicles at TAI. Mean concentrations of P4 during the 7‐day insertion period were greater (P<0.03) for new (3.7 ng/ml) and re‐used autoclaved (3.4 ng/ml) than for re‐used disinfected CIDRs (2.8 ng/ml). In summary, Presynch improved ovulation rate after GnRH‐1, but did not improve pregnancy rates compared to CO‐Synch + CIDR. Follicular maturity estimation was not feasible using VER as applied in this study. Autoclaving may be the best option when re‐using CIDR inserts because it creates greater concentrations of P4 during the first 48 h.

Objectives were to: 1) Evaluate the effectiveness of presynchronization with GnRH before the CO‐Synch + CIDR protocol with timed AI (TAI) at 66 h in Bos indicus‐influenced cattle; 2) Characterize ovarian events associated with the presynchronization; 3) Evaluate the efficacy of measuring vaginal electrical resistance (VER) to assess follicular maturity at TAI; and 4) Compare serum concentrations of progesterone (P4) in ovariectomized cows bearing new or previously used CIDR devices with or without autoclaving. In Exp. 1 and 2, cattle received either GnRH or saline on day ‐7. The CO‐Synch + CIDR protocol included a CIDR insert and GnRH (GnRH‐1; day 0), removal of CIDR and PGF2α on day 7, and GnRH (GnRH‐2) and TAI 66 h after CIDR removal. In Exp. 1, pregnancy rate of females with BCS ≥ 5 tended to differ (P=0.085) between Presynch (38%) and CO‐Synch + CIDR (54%). In Exp. 2, ovulatory response to GnRH‐1 was greater (P<0.01) in the Presynchronization (58%) than in the CO‐Synch + CIDR (27.1%) group. Emergence of a follicular wave after GnRH‐1 and ovulation rate after GnRH‐2 did not differ between groups. More (P<0.01) females that developed a follicular wave after GnRH‐1 ovulated (82%) after GnRH‐2, compared to those that did not (29%). Mean VER (ohms) was greatest (101.4±0.8) on day 0 and declined (P<0.01) to 95.2±0.8 and 82±0.8, respectively, on days 7 and 10. We observed a low negative but significant relationship (r=0.38; P<0.001) between VER and follicular size on day 0, 7, and 10. VER difference (day 10 minus day 7) did not differ between females with small and large follicles at TAI. Mean concentrations of P4 during the 7‐day insertion period were greater (P<0.03) for new (3.7 ng/ml) and re‐used autoclaved (3.4 ng/ml) than for re‐used disinfected CIDRs (2.8 ng/ml). In summary, Presynch improved ovulation rate after GnRH‐1, but did not improve pregnancy rates compared to CO‐Synch + CIDR. Follicular maturity estimation was not feasible using VER as applied in this study. Autoclaving may be the best option when re‐using CIDR inserts because it creates greater concentrations of P4 during the first 48 h.