Foetal and neonatal foal losses on equine herpesvirus type 1(EHV-1) infected farms before and after EHV-1 vaccination was introduced.

On 6 farms with a history of EHV-1 abortions the overall prevalence of losses due to abortion, stillbirth and neonatal foal mortality during 5 foaling seasons preceding the introduction of vaccination against EHV-1 were compared with corresponding data for 8 subsequent seasons in which all horses were immunized with a modified live EHV-1 vaccine. Although both sporadic and epizootic EHV-1 abortions occurred in immunized mares, the numbers of foetal and neonatal foal losses decreased significantly (chi 2 = 15.75; p less than 0.001) from 11.8% (343 of 2897 pregnancies) during the seasons 1969-1973 to 8.9% (334 of 3763 pregnancies) in the years 1975-1982 during which EHV-1 vaccinations had been carried out.