Foetal death in naive heifers inoculated with Neospora caninum isolate Nc-Spain7 at 110 days of pregnancy.

Neospora caninum infection is a leading cause of abortion in cattle worldwide. The pathogenesis of bovine neosporosis, particularly during the second term of gestation when most abortions occur in naturally infected dams, is poorly understood. In the present study foetal death was observed in 3 of 6 experimentally infected dams at 110 days of gestation after 6 weeks of experimental period. All experimental heifers were febrile between 3 and 5 days post infection (dpi). Inoculated dams seroconverted by 3-4 weeks post-infection with higher mean antibody titres in aborting dams compared to non-aborting heifers, although not significantly (p > 0.05). Neospora caninum DNA was detected in all infected foetuses and placentas, and three infected foetuses also had N. caninum antibodies. The parasite burden was higher in the brain of dead/aborted foetuses than in live foetuses. Interestingly, high IFN-γ production was detected in foetal fluids of a dead foetus found upon euthanasia of its dam, while no IFN-γ was observed in amniotic, allantoic and/or foetal fluids in the three infected foetuses that were alive upon maternal euthanasia. The present study confirms that the infection of dams on gestation day 110 with 10(7) tachyzoites of the Nc-Spain7 isolate causes abortion. The fact that some infected dams aborted and some did not is relevant to the understanding of N. caninum pathogenesis of abortion in naturally infected cows.

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.