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Title: Factors affecting pregnancy rate to estrous synchronization and fixed-time artificial insemination in beef cattle

Author
item Echternkamp, Sherrill
item Thallman, Richard - Mark

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2011
Publication Date: 10/1/2011
Citation: Echternkamp, S.E., Thallman, R.M. 2011. Factors affecting pregnancy rate to estrous synchronization and fixed-time artificial insemination in beef cattle. Journal of Animal Science. 89(10):3060-3068.

Interpretive Summary: Application of artificial insemination (AI) in extensive beef cattle production is limited by the necessity to monitor estrus and handle animals twice daily for several weeks. Protocols that effectively synchronize ovarian follicular development and ovulation to enable fixed-time AI (TAI) would facilitate the commercial use of AI. Methods to regulate ovulation in farm animals by changing or supplementing endogenous progesterone release have been investigated extensively for more than 50 yr, but the fertility of regulated estrous cycles is still variable. Objectives of the present study were to determine whether use of a controlled internal drug-release (CIDR) device to administer progesterone in a GnRH-based estrous synchronization protocol would optimize blood progesterone concentrations, improve synchronization of follicular development and estrus, and increase pregnancy rates to TAI. Postpartum beef cows received an injection of GnRH (100 µg i.m.) at the initiation of the treatment (d 0) followed by an injection of PGF (25 mg i.m.) 7 d later (CO-Synch treatment). One-half of the CO-Synch-treated cows receive a CIDR (1.38 mg progesterone) intravaginally on d 0, which was removed 7 d later at PGF injection (CO-Synch + CIDR). All cows were fixed-time AI at 60 h (range 59 to 62 h) after PGF injection regardless of estrus and received an injection of GnRH (100 µg i.m.) at AI. Inclusion of the CIDR device in the synchronization protocol increased pregnancy rate 10.3 percentage units compared with no CIDR (54.6 vs. 44.3%) and the proportion (66.7 vs. 57.8%) of cows detected in estrus before TAI. The increase in pregnancy rate with vs. without a CIDR was primarily for cows with small blood progesterone concentrations during treatment, reflective of no functional corpus luteum (CL); the difference was 34.4 percentage units. In contrast, fertility did not differ between protocols for cows having blood progesterone > 1 ng/mL on the last day of treatment (d 7). Although the CIDR increased pregnancy rate in cows with small or no progesterone secretion, lower pregnancy rate and estrus detection for cows with very elevated blood progesterone indicate that additional treatments are needed at the end of the synchronization protocol (d 7) to facilitate progesterone withdrawal in cows with enhanced CL function. In both treatments, pregnancy rate was greater for cows expressing estrus within 60 hrs before the TAI compared with cows not expressing estrus before AI. These results further emphasize the importance of synchronization of CL regression and progesterone withdrawal, maturation and ovulation of the ovulatory follicle, and timing of AI that is required for optimal fertility. Herd pregnancy rate for the TAI CO-Synch + CIDR synchronization protocol was about 10% less compared with the estimated pregnancy rate (64 %) for a conventional 21-day AI breeding programs with twice-daily estrus checks when assuming a pregnancy rate of 75% for a single AI service and an estrus-detection rate of 85% during a 21-day breeding period. Thus, the CO-Synch + CIDR synchronization protocol with TAI achieved pregnancy rates in beef cattle comparable to conventional AI programs and accomplished it with fewer human hours and better utilization of resources.

Technical Abstract: Application of AI in extensive beef cattle production is limited by the necessity to monitor estrus and handle animals twice daily for several weeks. Protocols that effectively synchronize ovarian follicular development and ovulation to enable fixed-time AI (TAI) would facilitate the use of AI. Objectives were to determine whether use of a controlled internal drug-release (CIDR) device to administer progesterone in a GnRH-based estrous synchronization protocol would optimize blood progesterone concentrations, improve synchronization of follicular development and estrus, and increase pregnancy rates to TAI. Beef cows (n = 1240) in 6 locations within the U.S. Meat Animal Research Center received 1 of 2 treatments: 1) an injection of GnRH (100 µg i.m.) followed by 25 mg PGF2 (PGF) i.m. 7 d later (CO-Synch), or 2) CO-Synch plus a CIDR during the 7 d between GnRH and PGF injections (CO-Synch + CIDR). Cows received TAI and were given GnRH (100 µg i.m.) at 60 h after PGF. Progesterone was measured by RIA in blood samples collected 2 wk before and at initiation of treatment (d 0) and at PGF injection (d 7). Estrous behavior was monitored by EstrotectTM Heat Detectors. Pregnancy was diagnosed by ultrasonography about 75 d after TAI; pregnancy rate to TAI did not differ among locations. Plasma progesterone did not differ between synchronization protocols at first GnRH injection (d 0; 3.8 ± 0.1 ng/mL) but was greater (P < 0.01) at PGF injection (d 7) in cows receiving CO-Synch + CIDR vs. CO-Synch (4.3 vs. 3.5 ± 0.1 ng/mL, respectively); fewer CIDR-treated cows had progesterone = 1 ng/mL at PGF (10.7 vs. 29.6%, respectively). A greater (P < 0.01) percentage of CO-Synch + CIDR vs. CO-Synch cows was detected in estrus within 60 h after PGF (66.7 vs. 57.8 ± 2.6%) and was pregnant to TAI (54.6 vs. 44.3 ± 2.6%, respectively). For cows with plasma progesterone = 1 ng/mL at PGF, the CIDR increased pregnancy rate (65.2 ± 5.9 vs. 30.8 ± 3.4% with vs. without CIDR) whereas pregnancy rates did not differ between protocols (52.1 ± 2.1 vs. 50.0 ± 2.4%, respectively) when progesterone was > 1 ng/mL (treatment x progesterone; P < 0.01). Inclusion of a CIDR in the synchronization protocol increased plasma progesterone concentration, proportion of cows detected in estrus, and pregnancy rate, but the increase in pregnancy rate with the CIDR was primarily in cows with declining or low endogenous progesterone secretion during treatment, reflective of CL regression.