Reproductive performance and its risk factors in Hanwoo cattle: a large-scale field study

Objective: This study aimed to identify factors affecting reproductive performance in Hanwoo cattle. Methods: A total of 4,656 artificial insemination records were analyzed to evaluate factors associated with pregnancy outcomes, pregnancy loss, the number of inseminations per conception, and the time to pregnancy. Results: The probability of pregnancy per artificial insemination was lower in cattle inseminated during spring compared with winter, and in heifers compared with cows. In contrast, pregnancy probability was higher in cattle with synchronization protocols including PGF2α-GnRH, modified Double-Ovsynch, and modified Presynch-Ovsynch compared with insemination after detected estrus. The risk of early pregnancy loss between 31 and 59 days of gestation was higher after the first insemination than after the second, while the risk of late pregnancy loss between 60 and 260 days was higher in heifers than in cows. The number of inseminations per conception was higher in heifers and in cattle experiencing early or late pregnancy loss. In addition, the use of modified Double-Ovsynch and modified Presynch-Ovsynch at the first insemination was associated with fewer inseminations than AI after detected estrus. The likelihood of pregnancy by 360 days postpartum was reduced in cows with intervals from calving to first insemination of 61 to 80 days or 81 days or more compared with cows inseminated within 60 days, and in cows that experienced early or late pregnancy loss. Conversely, the likelihood was higher in cows that calved during spring than in those that calved during winter. Conclusion: Heifer status, insemination during spring, and pregnancy loss negatively affected reproductive performance in Hanwoo cattle. In contrast, the use of synchronization protocols, earlier postpartum insemination, and spring calving were associated with improved reproductive outcomes. These findings support targeted interventions to improve reproductive efficiency in Hanwoo herds.