RESUMEN
Over a period of two years, a total of 22 full term foals from Welsh Mountain pony mares were raised in conditions that were free from infection by Equid herpesvirus (EHV-1/4). Parturition dates were predicted by monitoring colostrum electrolytes, and the mares allowed to foal naturally under supervision or following induction with intravenous oxytocin. Immediately following birth, foals were separated from their dams and transferred to a specially built, positive pressure isolation unit. They were given antibiotic prophylaxis and fed bovine colostrum during the first 24 h, and then mare's milk replacer until weaned. Out of 22 specific pathogen free (SPF) foals one that had not been given antibiotic prophylaxis died of an E. coli septicaemia aged eight days. Two foals developed a streptococcal upper respiratory tract infection, which responded to antibiotic therapy and did not spread to the rest of the herd. A self limiting upper respiratory tract infection was seen in a fourth foal and mild diarrhoea was observed in six foals. Physical development in all SPF foals appeared normal and behavioural patterns resembled those of conventional handreared foals. Newborn foals were held in a separate quarantine area, within the isolation unit, and checked extensively for evidence of EHV-1/4 infection, before being transferred to the main holding unit. Periodic checks were then made for EHV-1/4 over a period ranging from 2 to 4 months; none of the SPF foals showed evidence of infection with EHV-1/4 in terms of clinical disease, virus isolation, sero-conversion or specific lymphocyte transformation.