FSCR

The success of AI was confirmed by pregnancy diagnosis on day 60 post-insemination. The mixed-effects logistic regression model evaluating the association of FMD infection and FMD vaccination with FSCR is presented in Table 2. In Condition 1, FSCR decreased significantly after FMD infection compared with the pre-outbreak period (OR = 0.49; 95% CI: 0.35–0.70; p < 0.01). In contrast, no significant changes in FSCR were observed in Condition 2 (OR = 1.00; 95% CI: 0.39–2.54; p = 1.00) or Condition 3 (OR = 0.72; 95% CI: 0.45–1.14; p = 0.16).

Condition | Before, n pregnant/N | Estimated probability (95% CI) | After, n pregnant/N | Estimated probability (95% CI) | OR (After vs Before) | 95% CI | p-value
1 | 105/464 | 0.22 (0.18–0.27) | 59/464 | 0.12 (0.09–0.16) | 0.49 | 0.35–0.70 | <0.01
2 | 11/60 | 0.18 (0.10–0.30) | 11/60 | 0.18 (0.10–0.30) | 1.00 | 0.39–2.54 | 1.00
3 | 51/248 | 0.20 (0.15–0.26) | 39/248 | 0.15 (0.11–0.21) | 0.72 | 0.45–1.14 | 0.16

FSCR = First-service conception rate; OR = Odds ratio; CI = Confidence interval. The before period was used as the reference category for OR estimation within each condition. OR <1 indicates reduced odds of conception in the after period. Condition 1 = Heifers clinically affected by FMD during the outbreak; Condition 2 = Heifers developing clinical FMD after vaccination; Condition 3 = Clinically healthy heifers after vaccination.

Table 3 presents the exploratory post-exposure analysis based on the interval from clinical FMD onset or vaccination to the first post-exposure AI. In Condition 1, first AI within 90 days after clinical FMD onset was associated with substantially lower odds of first-service conception than AI performed after >90 days, with reductions ranging from approximately 84% to 91%. In Condition 2, a similar numerical trend was observed, with the odds of first-service conception within 90 days being approximately 74%–78% lower than those after >90 days; however, these differences were not statistically significant, likely because of the limited sample size. In Condition 3, first AI within 90 days after vaccination was also associated with lower odds of first-service conception, with reductions ranging from approximately 60% to 73% compared with AI performed after >90 days.

PR and S/C

Table 4 summarizes pregnancy outcomes and ORs before-and-after FMD infection or vaccination using mixed-effects logistic regression. In Condition 1, which included 464 heifers, the model-based estimated probability of pregnancy decreased from 0.57 before FMD infection to 0.37 after infection. The odds of conception after infection were significantly lower than those before infection (OR = 0.43; 95% CI: 0.33–0.57; p < 0.01). In Condition 2, which included 60 susceptible heifers that received FMD vaccination and subsequently developed clinical FMD, PRs were similar before-and-after vaccination. The model-based estimated probability of pregnancy was 0.45 before and 0.39 after vaccination, with no significant difference in PR (OR = 0.81; 95% CI: 0.38–1.69; p = 0.57). In Condition 3, which included 248 heifers, the model-based estimated probability of pregnancy decreased from 0.54 before vaccination to 0.45 after vaccination, and the odds of conception after vaccination were significantly lower than those before vaccination (OR = 0.69; 95% CI: 0.48–0.99; p = 0.04).

To our knowledge, this study provides the first quantitative field evidence showing that vaccination without subsequent clinical FMD was associated with only a modest 31% reduction in PR odds, compared with a 57% reduction after natural clinical FMD infection. Descriptively, S/C was slightly higher during the post-FMD period in Conditions 1 and 3, increasing from 2.19 ± 1.33 to 2.42 ± 1.39 and from 2.08 ± 1.12 to 2.38 ± 1.44, respectively. In contrast, little change was observed in Condition 2 (1.96 ± 1.04 vs. 2.00 ± 1.35).

Condition | Interval from FMD onset/ vaccination to first post-exposure AI | Pregnant/Total | FSCR (%) | OR vs >90 days | 95% CI | p-value
1 | 0–30 days | 0/11 | 0.00 | 0.09 | 0.01–1.59 | 0.02
 | 31–60 days | 3/57 | 5.26 | 0.12 | 0.04–0.39 | <0.01
 | 61–90 days | 7/98 | 7.14 | 0.16 | 0.07–0.37 | <0.01
 | >90 days | 95/298 | 31.88 | Reference | Reference | Reference
2 | 0–30 days | 0/4 | 0.00 | 0.26 | 0.01–5.38 | 0.55
 | 31–60 days | 1/13 | 7.69 | 0.20 | 0.02–1.81 | 0.24
 | 61–90 days | 1/12 | 8.33 | 0.22 | 0.02–1.98 | 0.24
 | >90 days | 9/31 | 29.03 | Reference | Reference | Reference
3 | 0–30 days | 3/30 | 10.00 | 0.27 | 0.08–0.96 | 0.03
 | 31–60 days | 7/50 | 14.00 | 0.40 | 0.16–0.98 | 0.05
 | 61–90 days | 5/43 | 11.63 | 0.32 | 0.12–0.89 | 0.02
 | >90 days | 36/125 | 28.80 | Reference | Reference | Reference

Condition | Before, n pregnant/N | Estimated probability (95% CI) | After, n pregnant/N | Estimated probability (95% CI) | OR (After vs Before) | 95% CI | p-value | S/C before | S/C after
1 | 265/464 | 0.57 (0.53–0.62) | 174/464 | 0.37 (0.33–0.42) | 0.43 | 0.33–0.57 | <0.01 | 2.19 ± 1.33 | 2.42 ± 1.39
2 | 27/60 | 0.45 (0.32–0.58) | 24/60 | 0.39 (0.28–0.53) | 0.81 | 0.38–1.69 | 0.57 | 1.96 ± 1.04 | 2.00 ± 1.35
3 | 133/248 | 0.54 (0.47–0.60) | 111/248 | 0.45 (0.38–0.51) | 0.69 | 0.48–0.99 | 0.04 | 2.08 ± 1.12 | 2.38 ± 1.44