Evaluation of administration of West Nile virus vaccine to pregnant broodmares.

The research investigates whether administering a vaccine for West Nile virus to pregnant mares (female horses) was linked to pregnancy loss. The results showed no evidence of increased pregnancy loss associated with the vaccination process.

Methodology

• The research was a retrospective cohort study, looking back at the historical data for a group of mares.
• The study focused on 595 mares from 4 different farms with known vaccination history.
• The records reviewed included details about each mare’s identification, breed, reproductive status, last breeding date, the last known pregnant date, and vaccination date.
• Information about the age of the embryo at the time of vaccination and instances of early embryonic death (EED), early fetal loss (EFL), or late fetal loss (LFL) were recorded.
• The study took into account whether the vaccination was administered during the early embryonic, early fetal, or late fetal period of the pregnancy.

Results and Interpretation

• The research found no association between vaccination during any period of gestation and an increase in pregnancy loss (EED, EFL, LFL).
• The data did not support the theory that vaccination could lead to an increased incidence in pregnancy loss.

Conclusions and Implications

• The study provided evidence suggesting that vaccination against West Nile virus will not compromise pregnancy in horses.
• It is important to note that many mares are already pregnant when mosquito season starts – the time when they’re more likely to be vaccinated against the West Nile virus.
• These findings offer reassurance to horse breeders and veterinarians that the vaccination can be safely administered to pregnant mares without the risk of causing fetal loss.