title: Fertility of Angus cross beef heifers after GnRH treatment on day 23 and timing of insemination in 14-day CIDR protocol.
abstract: This study compared artificial insemination pregnancy rate (AI-PR) between 14-day CIDR-GnRH-PGF2α-GnRH and CIDR-PGF2α-GnRH synchronization protocol with two fixed AI times (56 or 72 hr after PGF2α). On day 0, heifers (n = 1311) from nine locations assigned body condition score (BCS: 1, emaciated; 9, obese), reproductive tract score (RTS: 1, immature, acyclic; 5, mature, cyclic) and temperament score (0, calm; and 1, excited) and fitted with a controlled internal drug release (CIDR, 1.38 g of progesterone) insert for 14 days. Within herd, heifers were randomly assigned either to no-GnRH group (n = 635) or to GnRH group (n = 676), and heifers in GnRH group received 100 μg of GnRH (gonadorelin hydrochloride, IM) on day 23. All heifers received 25 mg of PGF2α (dinoprost, IM) on day 30 and oestrous detection aids at the same time. Heifers were observed for oestrus thrice daily until AI. Within GnRH groups, heifers were randomly assigned to either AI-56 or AI-72 groups. Heifers in AI-56 group (n = 667) were inseminated at 56 hr (day 32 PM), and heifers in AI-72 group (n = 644) were inseminated at 72 hr (day 33 AM) after PGF2α administration. All heifers were given 100 μg of GnRH concurrently at the time AI. Controlling for BCS (p < .05), RTS (p < .05), oestrous expression (p < .001), temperament (p < .001) and GnRH treatment by time of insemination (p < .001), the AI-PR differed between GnRH treatment [GnRH (Yes - 60.9% (412/676) vs. No - 55.1% (350/635); p < .05)] and insemination time [AI-56 - 54.6% (364/667) vs. AI-72 - 61.8% (398/644); (p < .01)] groups. The GnRH treatment by AI time interaction influenced AI-PR (GnRH56 - 61.0% (208/341); GnRH72 - 60.9% (204/335); No-GnRH56 - 47.9% (156/326); No-GnRH72 - 62.8% (194/309); p < .001). In conclusion, 14-day CIDR synchronization protocol for FTAI required inclusion of GnRH on day 23 if inseminations were to be performed at 56 hr after PGF2α in order to achieve greater AI-PR.
authors.affiliation: Department of Veterinary Clinical Sciences, Washington State University, Pullman, WA, USA.
authors.forename: R K
authors.initials: RK
authors.lastname: Kasimanickam
authors.affiliation: Nancy M. Cummings Nancy M Cummins Research Extension and Education Center, University of Idaho, Carmen, ID, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: Hall
authors.affiliation: Department of Large Animal Clinical sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.
authors.forename: W D
authors.initials: WD
authors.lastname: Whittier
mesh_terms: D000818:Animals; D002417:Cattle; D015237:Dinoprost / Q000008:administration & dosage*; D004971:Estrus / Q000187:drug effects*; D004972:Estrus Detection; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D005298:Fertility / Q000187:drug effects*; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage*; D007315:Insemination, Artificial / Q000662:veterinary*; D011247:Pregnancy; D018873:Pregnancy Rate
chemical_list: D007987:Gonadotropin-Releasing Hormone; D015237:Dinoprost