Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: February 19, 2009
Publication Date: July 1, 2009
Citation: Echternkamp, S.E., Hays, W.G., Jones, S., Cushman, R.A. 2009. Comparison of Two Protocols to Achieve Pregnancy to Fixed-Time Artificial Insemination (TAI) in Suckled Beef Cows [abstract]. Journal of Animal Science. 87 (E-Supplement 2):269 (Abstract # T228). Technical Abstract: Application of AI in extensive beef cattle production has been limited by the necessity to monitor estrus and handle animals twice daily for several weeks. Protocols that proficiently synchronize ovarian follicular development and ovulation to enable fixed-time artificial insemination (TAI) would facilitate use of AI. The objective was to determine whether adding a controlled internal drug-release device (CIDR) to a GnRH-based protocol increased blood progesterone (P4) concentrations and ovarian synchrony, thus increasing pregnancy rate to TAI. Cyclic suckled beef cows (n = 1238) 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, followed by GnRH (100 µg i.m.) 60 h after PGF (CO-Synch), or 2) Co-Synch plus a CIDR during the 7-d interval between GnRH and PGF injections (Co-Synch + CIDR). All cows were bred by TAI 60 h after PGF. Cows were fitted with an Estrotect heat detector and estrus was recorded during treatment and at TAI. Blood samples were collected at GnRH (first) and PGF injections; P4 was assayed in plasma by RIA. Pregnancy was diagnosed 70 to 90 d after AI. Progesterone did not differ between treatments at first GnRH (4.0 + 0.1 ng/mL) but was greater (P < 0.01) at PGF injection in Co-Synch + CIDR- vs. Co-Synch-treated cows (4.6 vs. 3.5 + 0.1 ng/mL, respectively), and fewer CIDR-treated cows had P4 concentrations < 1 ng/mL at PGF (10.7 vs. 28.4 + 1.0%, respectively). A greater (P < 0.01) percentage of Co-Synch + CIDR- vs. Co-Synch-treated cows expressed estrus (63.4 vs. 54.4 + 2.0%) and were pregnant to TAI (53.5 vs. 43.2 + 2.0%, respectively). For cows having P4 < 1 ng/mL at PGF, the CIDR increased pregnancy rate (59.1 vs. 27.6 + 2.0% with vs. without CIDR), whereas pregnancy rates did not differ between treatments for cows with P4 >1 ng/mL. Inclusion of a CIDR in the synchronization protocol increased plasma P4 concentrations, expression of estrus, and pregnancy rates, primarily in cows with low endogenous progesterone secretion.