title: Comparison of three CIDR-based fixed-time AI protocols in beef heifers.
abstract: Several effective fixed-time AI (FTAI) protocols have been developed to facilitate AI in beef heifers that circumvent the need for estrus detection. Among these are the 5-d CO-Synch + controlled intravaginal progesterone insert (CIDR) protocol (5dCO), PGF2α (PG) 6-d CIDR protocol (PG-6dCIDR), and 14-d CIDR-PG protocol (14dCIDR-PG). Although each of these protocols varies in duration and approach to synchronizing estrus and ovulation, each has been reported as an effective method to facilitate FTAI in beef heifers. Therefore, the objective of this study was to compare FTAI pregnancy rates in beef heifers synchronized with these 3 CIDR-based protocols. Virgin beef heifers (n = 801) at 4 locations were synchronized with 1 of 3 protocols: 1) 5dCO, an injection of GnRH (100 μg) and insertion of a CIDR on d -5, PG (25 mg) and CIDR removal on d 0 with a second injection of PG (>4 h after CIDR removal) on d 0 and FTAI at 72 h after CIDR removal, 2) PG-6dCIDR, PG (25 mg) on d -9, GnRH (100 μg) and insertion of a CIDR on d -6, PG and CIDR removal on d 0, and FTAI at 66 h after CIDR removal, or 3) 14dCIDR-PG, a 14-d CIDR insert from d -30 to -16, PG (25 mg) on d 0, and FTAI at 66 h after PG. All heifers received an injection of GnRH (100 μg) concurrent with FTAI. Timing of treatment initiation was offset to allow all heifers to receive FTAI concomitantly and at random. Pregnancy success was determined between 35 and 40 d after FTAI by transrectal ultrasonography. Blood samples were collected before the beginning of each protocol and at the initiation of each protocol to determine estrous cycling status (77%). Data were analyzed using the GLIMMIX procedures of SAS. As expected, because of the duration of protocols, fewer heifers in the 14dCIDR-PG treatment were pubertal at initiation of synchronization than in the 5dCO (P < 0.05) and PG-6dCIDR (P = 0.10) treatments. Fixed-time AI pregnancy success did not differ between treatments (P = 0.14; 62.6%, 56.9%, and 53.3% for 5dCO, PG-6dCIDR, and 14dCIDR-PG, respectively). However, heifers that had reached puberty by initiation of synchronization had greater (P < 0.01) pregnancy success compared to heifers that were prepubertal (60.7% and 47.3%, respectively). In summary, all 3 protocols had similar FTAI pregnancy success, and puberty status had the greatest impact on pregnancy success.
authors.affiliation: North Central Research and Outreach Center, University of Minnesota, Grand Rapids 55744 gbridges@umn.edu.
authors.forename: G A
authors.initials: GA
authors.lastname: Bridges
authors.affiliation: Department of Animal Science, University of Wyoming, Laramie 82071.
authors.forename: S L
authors.initials: SL
authors.lastname: Lake
authors.affiliation: North Central Research and Outreach Center, University of Minnesota, Grand Rapids 55744.
authors.forename: S G
authors.initials: SG
authors.lastname: Kruse
authors.affiliation: North Central Research and Outreach Center, University of Minnesota, Grand Rapids 55744.
authors.forename: S L
authors.initials: SL
authors.lastname: Bird
authors.affiliation: North Central Research and Outreach Center, University of Minnesota, Grand Rapids 55744.
authors.forename: B J
authors.initials: BJ
authors.lastname: Funnell
authors.affiliation: Department of Animal Science, University of Wyoming, Laramie 82071.
authors.forename: R
authors.initials: R
authors.lastname: Arias
authors.affiliation: Department of Animal Science, South Dakota State University, Brookings 57006.
authors.forename: J A
authors.initials: JA
authors.lastname: Walker
authors.affiliation: Department of Animal Science, South Dakota State University, Brookings 57006.
authors.forename: J K
authors.initials: JK
authors.lastname: Grant
authors.affiliation: Department of Animal Science, South Dakota State University, Brookings 57006.
authors.forename: G A
authors.initials: GA
authors.lastname: Perry
mesh_terms: D000282:Administration, Intravaginal; D000818:Animals; D002417:Cattle; D003692:Delayed-Action Preparations; D004971:Estrus / Q000187:drug effects; D004972:Estrus Detection / Q000379:methods; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage* / Q000494:pharmacology
chemical_list: D003692:Delayed-Action Preparations; D011374:Progesterone
keywords: Beef heifers; CIDR; estrous synchronization; fixed-time AI