Differential effects of foot-and-mouth disease infection and vaccination on fertility of Holstein-Friesian heifers: Evidence from a within-animal retrospective study in Indonesia.

Abstract

Background and aim: Foot-and-mouth disease (FMD) remains one of the most economically important transboundary diseases affecting livestock worldwide. Following its re-emergence in Indonesia in 2022 after more than three decades of freedom, concerns arose regarding its impact on dairy cattle fertility and the possible reproductive consequences of emergency vaccination. However, field-based evidence directly comparing the reproductive effects of natural FMD infection and vaccination within the same animals is lacking. This study evaluated the association of clinical FMD infection and inactivated FMD vaccination with reproductive performance in Holstein-Friesian heifers using a within-animal retrospective design.

Materials and methods: A retrospective within-animal before-and-after study was conducted using reproductive records from 772 Holstein-Friesian heifers maintained by 501 smallholder dairy farmers in Malang Regency, East Java, Indonesia. Reproductive performance during two consecutive 180-day periods before-and-after FMD infection or vaccination was compared within the same animals. Heifers were classified into three conditions: clinical FMD during the outbreak (n = 464), clinical FMD after the first vaccination (n = 60), and vaccinated heifers remaining clinically healthy (n = 248). First-service conception rate (FSCR) and pregnancy rate (PR) were analyzed using mixed-effects logistic regression, whereas first-service-to-conception interval (FSCI) and reproductive record exit were evaluated using Kaplan-Meier and Cox proportional hazards models.

Results: Clinical FMD infection significantly impaired reproductive performance. In condition 1, FSCR and PR decreased significantly after infection (FSCR: odds ratio [OR] = 0.49, 95% confidence interval [CI]: 0.35-0.70, p < 0.01; PR: OR = 0.43, 95% CI: 0.33-0.57, p < 0.01). The hazard of conception was also significantly reduced (hazard ratio = 0.56, 95% CI: 0.46-0.67, p < 0.01), with the median FSCI increasing from 27.5 to 45 days. Vaccinated heifers that subsequently developed clinical FMD showed no significant deterioration in reproductive performance. Vaccinated clinically healthy heifers exhibited only a modest reduction in PR (OR = 0.69, 95% CI: 0.48-0.99, p = 0.04), while FSCR remained unchanged. Exploratory analysis indicated that artificial insemination performed >90 days after infection or vaccination was associated with improved conception outcomes.

Conclusion: Natural FMD infection substantially reduced fertility in Holstein-Friesian heifers, whereas vaccination produced comparatively minor and less consistent reproductive effects. These findings support continued FMD vaccination programs while highlighting the importance of integrating vaccination schedules with reproductive management to minimize fertility losses during FMD outbreaks.