CONCLUSION

This retrospective within-animal before-and-after study demonstrated that natural FMD infection had a substantially greater detrimental effect on reproductive performance in HF heifers than FMD vaccination under smallholder dairy production systems in Indonesia. Heifers with clinical FMD during the outbreak exhibited significant reductions in FSCR and PR, together with delayed conception, indicating persistent impairment of reproductive efficiency following natural infection. In contrast, FMD vaccination was associated with relatively minor reproductive effects. Vaccinated heifers that remained clinically healthy showed only a modest reduction in PR, with no significant deterioration in FSCR. Furthermore, exploratory interval analyses suggested that delaying the first AI until more than 90 days after FMD infection or vaccination was associated with improved first-service conception outcomes, highlighting the importance of appropriate reproductive timing following disease exposure or immunization.

The principal strength of this study lies in its within-animal design, in which each heifer served as its own control, thereby minimizing confounding arising from individual genetic, physiological, and management differences. In addition, the large field-based dataset collected during the 2022 Indonesian FMD outbreak provides practical evidence directly applicable to smallholder dairy production systems. Nevertheless, interpretation of the findings should consider the retrospective nature of the study, the absence of several potentially important confounding variables, and the use of a proxy definition for reproductive record exit because complete culling records were unavailable.

From a practical perspective, the findings indicate that the reproductive consequences of natural FMD infection considerably outweigh the relatively limited effects associated with vaccination. These results support the continued implementation of FMD vaccination programs while emphasizing the importance of integrating vaccination schedules with reproductive management, particularly by avoiding insemination during the early post-vaccination or post-infection period whenever possible. Future prospective, multicenter studies incorporating endocrine, metabolic, and immunological biomarkers are warranted to clarify the biological mechanisms underlying FMD-associated reproductive impairment and to determine the optimal timing of breeding following infection or vaccination. Overall, maintaining effective vaccination programs together with appropriate reproductive management remains essential for minimizing fertility losses and improving the productivity and sustainability of dairy herds in FMD-endemic regions.