title: Effect of gonadotropin-releasing hormone or prostaglandin F(2α)-based estrus synchronization programs for first or subsequent artificial insemination in lactating dairy cows.
abstract: The objective was to evaluate the effects of GnRH or PGF(2α)-based synchronization and resynchronization programs on fertility in lactating dairy cows. For experiment 1, cows (n=1,521) were presynchronized with 2 injections of PGF given at 36 and 50 DIM and assigned to 1 of 3 protocols: Ovsynch [OVS; n=552; GnRH injection, PGF(2α) injection 7 d later, GnRH injection 56 h later, and timed artificial insemination (TAI) 16 h later] beginning at 14 d after presynchronization (PS), GnRH-GnRH-PGF(2α)-GnRH (GGPG; n=402) treatment with a GnRH injection given 7 d after PS and OVS 7 d later, or PGF(2α)-GnRH-PGF(2α)-GnRH (P7GPG; n=567) treatment with a PGF(2α) injection given 7 d after PS and OVS beginning 7 d later. Experiment 2 cows (n=2,327) were assigned to 1 of 3 resynchronization protocols 7 d before nonpregnancy diagnosis (NPD): GGPG cows (n=458) received a GnRH injection at enrollment and OVS at NPD; P7GPG cows (n=940) received a PGF(2α) injection at NPD and OVS 7 d later; and P11GPG cows (n=929) received a PGF(2α) injection 3 d after NPD and OVS 11 d later. In both experiments, cows were artificially inseminated upon estrus detection (ED). In experiment 1, 52.3% of cows were artificially inseminated upon ED, with GGPG having reduced ED (GGPG=46.8 vs. OVS=50.7 and P7GPG=57.7%). Treatments did not affect overall pregnancy per artificial insemination (P/AI) at 36 and 66 d after AI (OVS=34.1 and 32.3, P7GPG=34.6 and 31.9, and GGPG=31.3 and 28.1%, respectively) or pregnancy loss but cows artificially inseminated upon ED had higher P/AI than cows undergoing TAI (ED cows=37.9 vs. TAI cows=28.8%). Treatment did not affect P/AI for cows artificially inseminated upon ED or TAI at 36 and 66 d after AI (OVS=34.1 and 32.3, P7GPG=34.6 and 31.9, and GGPG=31.3 and 28.1%). Median days in milk at first AI was affected by treatment (P7GPG=59 vs. OVS=68 and GGPG=68 d). In experiment 2, GGPG reduced ED (GGPG=23.3 vs. P7GPG=74.9 and P11GPG=79.6%). Treatment did not affect overall P/AI at 36 and 66 d after AI (GGPG=29.2 and 25.8, P7GPG=28.7 and 26.6, and P11GPG=31.9 and 30.2%) or pregnancy loss. Cows artificially inseminated upon ED had greater P/AI than TAI cows (ED=32.3 and TAI=25.1%). However, treatment did not affect P/AI for cows artificially inseminated upon ED at 36 and 66 d after AI (GGPG=29.6 and 27.3, P7GPG=29.4 and 28.1, and P11GPG=35.7 and 33.7%) or TAI (GGPG=29.1 and 25.3, P7GPG=25.0 and 22.1, and P11GPG=16.9 and 16.9%). Median days between NPD and AI was affected by treatment (GGPG=10 vs. P7GPG=4 and P11GPG=7 d). Prostaglandin-based programs increased ED and reduced interval to first AI and between AI. Gonadotropin-releasing hormone-based programs increased the proportion of TAI cows. Cows artificially inseminated upon ED had increased P/AI compared with TAI cows.
authors.affiliation: Texas A&M AgriLife Research and Extension, Texas A&M System, Stephenville TX 76401, USA.
authors.forename: R G S
authors.initials: RG
authors.lastname: Bruno
authors.forename: A M
authors.initials: AM
authors.lastname: Farias
authors.forename: J A
authors.initials: JA
authors.lastname: Hernández-Rivera
authors.forename: A E
authors.initials: AE
authors.lastname: Navarrette
authors.forename: D E
authors.initials: DE
authors.lastname: Hawkins
authors.forename: T R
authors.initials: TR
authors.lastname: Bilby
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000494:pharmacology*; D004972:Estrus Detection / Q000379:methods; D004973:Estrus Synchronization / Q000379:methods* / Q000502:physiology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D007774:Lactation / Q000187:drug effects / Q000502:physiology; D010298:Parity / Q000187:drug effects / Q000502:physiology; D011247:Pregnancy / Q000187:drug effects / Q000502:physiology
chemical_list: D007987:Gonadotropin-Releasing Hormone; D015237:Dinoprost