Evaluation of the safety of vaccinating mares against equine viral arteritis during mid or late gestation or during the immediate postpartum period.

This research study investigates the safety of vaccinating horses against equine viral arteritis (EVA) during different stages of pregnancy and immediately after birth. The findings reveal that it may be safe to vaccinate healthy pregnant horses up to three months before giving birth and immediately after, but vaccinating during the last two months of pregnancy may increase the risk of abortion.

Study Design and Methodology

• In this randomized controlled study, 73 pregnant and postpartum mares, along with their foals, were used as the test subjects.
• The pregnant mares were vaccinated either during mid pregnancy, late pregnancy, or two to three days after giving birth.
• The vaccine used was a commercially available modified-live virus vaccine against the equine viral arteritis (EVA).
• The impact of the vaccination on the health of the mares and their foals was evaluated by monitoring the birth outcomes and through testing serum, blood, milk, and nasopharyngeal samples for signs of adverse response.

Results and Findings

• All mares that were vaccinated during the mid-pregnancy period gave birth without any complications, with 21 out of 22 mares developing antibody titers against EAV before foaling.
• Out of the 19 mares vaccinated during the late pregnancy period, 3 experienced abortion. However, antibody titers against EAV were still detected in 13 out of 15 mares at the time of foaling.
• All mares vaccinated immediately after giving birth were seronegative at the time of foaling but seroconverted after vaccination. Notably, no negative effects were observed in any of their foals.

Conclusions and Implications

• The research implies that pregnant mares can safely receive EVA vaccination up till three months before giving birth and immediately after parturition, if the risk of natural EVA exposure is substantial.
• The study found an associated risk of abortion when mares were vaccinated during the final two months of gestation, highlighting a need for weighing this risk against the also significant risk of widespread abortion due to natural EVA infection in unprotected mare populations.