We aimed to evaluate whether a modified pre-synchronization-Ovsynch (MPO) and resynchronization method, adjusted for the timing of biweekly reproductive consulting visits, could be implemented successfully under field conditions in dairy herds. Forty-five days after calving (calving: Day 0), 1,182 cows were assigned randomly to Ovsynch, MPO or control groups. (1) Cows were administered GnRH on Day 65, PGF2α on Day 72 and GnRH 56 hr later, followed by timed artificial insemination (TAI) 16 hr later (Ovsynch, n = 380). (2) Cows with a CL were administered PGF2α (n = 204) and cows without were administered GnRH (n = 199) on Day 45. Then, each cow was administered PGF2α on Day 55 (9 to 12 days later), GnRH on Day 58 and underwent Ovsynch 7 days later (selective MPO [sMPO] n = 403). (3) The remaining cows underwent AI when oestrus was detected (EDAI, n = 399). The probabilities of pregnancy per AI 30 and 45 days after the first AI were higher in the sMPO group (odds ratios 1.99 and 1.92, p < .0001) than in the EDAI group. In addition, the probability of pregnancy by 105 days postpartum tended to be higher (p < .1) in the sMPO group than in the EDAI and Ovsynch groups, which shortened the mean interval from calving to pregnancy in the sMPO group (3.4 and 4.2 days, respectively) than in the EDAI and Ovsynch groups. In the sMPO group, the interval between the first and second treatments during pre-synchronization did not affect the probability of pregnancy per AI after the first AI. The probability of pregnancy per AI after the second AI did not differ between the Ovsynch, sMPO and EDAI groups. In conclusion, the sMPO programme, adjusted for the timing of biweekly reproductive consulting visits, followed by resynchronization, could be successfully adopted in field conditions, and is associated with good reproductive performance in dairy herds.
Keywords: Ovsynch; dairy cow; reproductive strategy; selective pre-synchronization.
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