title: Double-Ovsynch, compared with presynch with or without GnRH, improves fertility in heat-stressed lactating dairy cows.
abstract: The objective was to compare 3 timed artificial insemination (TAI) protocols in lactating dairy cows during heat stress. Multiparous Holstein cows yielding (mean ± SEM) 29.4 ± 0.3 kg of milk/d randomly were assigned to 1 of 3 TAI protocols at 34 ± 5.1 days in milk: 1) double-Ovsynch (DO; n = 486): the cows received GnRH-7d-2α-3d-GnRH and Ovsynch56 (GnRH-7d-PGF2α-56h-GnRH-16h-AI) was initiated 7 days later; 2) Presynch-GnRH-Ovsynch (PGO; n = 453): the cows received PGF2α-14d-PGF2α-2d-GnRH and Ovsynch56 was initiated 7 days later; and 3) presynch-Ovsynch (PO; n = 435): the cows received PGF2α-14d-PGF2α and Ovsynch56 was initiated 12 days later. The ovulatory response to the first GnRH of Ovsynch56 was higher in DO (65.0%) compared to PGO (53.2%) and PO (45.5%). Luteolytic response to PGF2α of Ovsynch was similar among TAI protocols (90.1%, 87.1%, and 86.2% for DO, PGO, and PO, respectively). Synchronization rate was greater in DO (86.2%) than in PGO (78.1%) and PO (72.1%) protocols. Irrespective of the TAI protocol, cows that ovulated in response to first GnRH had greater response to PGF2α (92.7 vs. 77.1%). Mean (±SEM) diameter (mm) of ovulatory follicle at TAI was larger in DO (16.1 ± 0.3) than PGO (15.6 ± 0.21) and PO (15.2 ± 0.12). Cows subjected to DO had greater P/AI at 32 days and at 60 days after TAI (26.6 and 24.4%) compared with those in PGO (21.4 and 20.0%) and PO (17.2 and 15.9%). However, TAI protocol had no significant effect on the incidence of pregnancy loss (6.1%, 6.6%, and 7.4% for DO, GO, and PO, respectively). In summary, cows in the DO protocol had a greater ovulation rate to the first GnRH and a greater synchronization rate, larger ovulatory follicles and greater P/AI. Of the 3 protocols used, DO yield the best reproductive performance in heat-stressed, lactating dairy cows.
authors.affiliation: Department of Animal Science, Sari Agricultural Sciences and Natural Resources University, Sari, Mazandaran, Iran. Electronic address: Dirandeh@gmail.com.
authors.forename: E
authors.initials: E
authors.lastname: Dirandeh
authors.affiliation: Department of Animal Science, University of Tehran, Karaj, Alborz, Iran.
authors.forename: A Rezaei
authors.initials: AR
authors.lastname: Roodbari
authors.affiliation: Livestock Research Branch, Alberta Agriculture and Rural Development, Edmonton, AB, Canada.
authors.forename: M G
authors.initials: MG
authors.lastname: Colazo
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D018869:Heat-Shock Response; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D010062:Ovulation Induction / Q000379:methods / Q000662:veterinary; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000662:veterinary
chemical_list: D007987:Gonadotropin-Releasing Hormone
keywords: Dairy cows; Double-Ovsynch; Heat stress; Presynch-Ovsynch; Timed-AI protocols