SEROPREVALENCE OF EQUINE HERPESVIRUS-1 IN THOROUGHBRED FOALS BEFORE AND AFTER WEANING

Objective To investigate the seroprevalence of equine herpesvirus I in foals around weaning and after weaning on two large Thoroughbred farm s using a type-specific enzyme-linked immunosorbent assay to determine exposure to infection. Design A longitudinal population study in grou ps of Thoroughbred weanling foals Study population Two hundred weanlin g Thoroughbred foals from a population of about 380 foals were enrolle d on two adjacent stud farms in the Hunter Valley of New South Wales. Foals on both farms were weaned from February to May 1995 into randoml y selected groups of 10 to 15 foals. Farms were selected because of th eir willingness to cooperate in the survey and because their detailed records of foals and their movements. They were representative of well -managed large Thoroughbred stud farms in New South Wales. Both studs had upper respiratory tract disease among weanling foals around weanin g each year although the seroprevalence of viral respiratory disease o n either farm was not known before the study. Procedure Serum was coll ected from foals within each group at fortnightly intervals from 9th F ebruary until Ist June 1995, and at a single follow-up period in Augus t 1995. Each sample was tested in triplicate using an antibody-detecti on ELISA which is type-specific for EHV-1 and EHV-4 antibodies. Result s and conclusions There was serological evidence of EHV-1 infection bo th before and after weaning. The prevalence of EHV-1 antibody in the s ample population increased during the study and individual cases of EH V-1 infection were identified. The increase was caused both by the ser oconversion of foals within the groups and by the recruitment into the study of foals with pre-existing EHV-1 antibody. Evidence of EHV-1 in fection in Thoroughbred foals after weaning has not been reported prev iously in Australia and this has implications for vaccination regimens .