Commingling of horses from various populations, together with physiological stress associated with transport and confinement at a sales complex, may be associated with detection and transmission of equine herpesvirus type-1 (EHV-1) and -4 (EHV-4). This prospective cohort study aimed to investigate the currently undefined prevalence of EHV-1 and -4 in young Thoroughbreds at an auction sale in South Africa, and associations between clinical signs, physiological stress and viral detection. Ninety, two-year old Thoroughbreds (51 colts, 39 fillies) were consigned from eight farms and sampled at a South African auction sale. The horses were monitored for pyrexia and nasal discharge. Nasal swabs were collected for quantitative polymerase chain reaction (qPCR) assay to detect EHV-1 and -4 and faecal samples were collected for enzyme immunoassay (EIA) to determine faecal glucocorticoid metabolite (FGM) concentrations. EHV-4 nucleic acid was detected in some and EHV-1 nucleic acid in none of the population. Pyrexia and nasal discharge were poor indicators of EHV-4 status. Variation in FGM concentrations was best explained by transportation and preparation for auction. Peaks in EHV-4 detection and increases in FGM concentrations were identified shortly post-arrival and on the first day of auction. Temporal changes in FGM concentrations of horses from individual farms showed two distinct patterns: Pattern A (biphasic peaks) and Pattern B (single peak). It was concluded that sales consignment was associated with some EHV-4 nucleic acid detection and distinctive physiological stress patterns in this population of young Thoroughbreds. / Dissertation (MSc)--University of Pretoria, 2014. / tm2015 / Companion Animal Clinical Studies / MSc / Unrestricted