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This study was designed to identify the factors affecting reproductive outcomes in lactating dairy cows undergoing Presynchronization-Ovsynch and successive resynchronization programs. Data were collected from 1,458 cows on 11 dairy farms, regarding nutrition, health, reproduction, and specifically reproductive programs used for the first timed artificial insemination (TAI; Modified Presynch-Ovsynch or Modified Double-Ovsynch) and for re-inseminations (Ovsynch or PreGnRH-Ovsynch); as well as the weather. Body condition score (BCS) and timing of TAI affected (P 0.01) the probability of pregnancy per AI after first TAI. Cows with a BCS ≥3.25 were more likely (P 0.01) to be pregnant at 31 (odds ratio [OR]: 1.85) and 49 (OR: 1.93) days after the first TAI than cows with BCS ≤2.75. Cows inseminated during months of heat stress (June to September) were less likely (P 0.01) to be pregnant at 31 (OR: 0.74) and 49 (OR: 0.68) days after first TAI than those inseminated during months of no heat stress (October to May). Cows that had a pre- or postpartum disorder were more likely to lose their pregnancy (OR: 2.17, P 0.01) than those that did not. Cows inseminated ≥76 days after calving (OR: 1.67, P 0.1) or during the months of heat stress (OR: 2.02, P 0.05) were also more likely to lose pregnancy than cows inseminated ≤75 days after calving or during the months of no heat stress. Following successive resynchronizations, cows with a third (OR: 1.32, P 0.1) or fourth (OR: 1.68, P 0.05) TAI were more likely to be pregnant than those with a second TAI. Cows with BCS ≥3.25 at the beginning of resynchronization were more likely (OR: 1.49, P 0.05) to be pregnant than cows with BCS ≤2.75. Finally, the likelihood of being pregnant by 210 days postpartum was positively associated with a favorable BCS, but negatively associated with the presence of a pre- or postpartum disorder and a larger number of days to first TAI following calving (≥76 vs. ≤75 days). In conclusion, high BCS has beneficial effects during the entire reproductive period, whereas TAI during heat stress, the presence of a pre- or postpartum disorder, a larger number of days to first TAI following calving, and TAI number (second or ≥ fifth) adversely affects the outcomes associated with pregnancy during the early or later breeding periods in lactating dairy cows undergoing Presynchronization-Ovsynch and successive resynchronization programs. |
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