Double-Ovsynch, compared with presynch with or without GnRH, improves fertility in heat-stressed lactating dairy cows

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-2 alpha-3d-GnRH and Ovsynch56 (GnRH-7d-PGF2 alpha-56h-GnRH-16h-AI) was initiated 7 days later; 2) PresynchGnRH-Ovsynch (PGO; n = 453): the cows received PGF2 alpha-14d-PGF2 alpha-2d-GnRH and Ovsynch56 was initiated 7 days later; and 3) presynch-Ovsynch (PO; n = 435): the cows received PGF2 alpha-14d-PGF2 alpha 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 PGF2 alpha 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 PGF2 alpha (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. (C) 2015 Elsevier Inc. All rights reserved.