Effects of long-term vaccination against Coxiella burnetii on the fertility of high-producing dairy cows.

The impact of long-term vaccination against Coxiella burnetii on the fertility of cows was studied. Double vaccinations three weeks apart at the start of the third trimester of gestation in each of two consecutive pregnancies were applied. The final study population consisted of 410 cows after the first vaccination round. Based on the odds ratios, the likelihood of early fetal loss (pregnancy loss following a positive pregnancy diagnosis before Day 90 of gestation) was higher in control cows (OR = 1.42) than in vaccinated cows. The final study population consisted of 336 cows after the second round of vaccination. According to the odds ratios, vaccinated C. burnetii seronegative cows were less likely to be subfertile (> 3 AI) (OR = 0.4) compared to non-vaccinated seronegative animals, and the likelihood of early fetal loss was lower in vaccinated C. burnetii seropositive animals (OR = 0.3) compared to non-vaccinated seronegative cows. Seropositivity to C. burnetii was positively related to twin pregnancy after the two rounds of vaccination (OR = 2.1 and 3.5, respectively). These results indicate that two consecutive vaccination rounds against C. burnetii in advanced gestation reduce subfertility and early fetal loss in dairy cows.