To isolate a horse is to remove it from contact with other horses — and ideally from shared airspace, water sources, and equipment — to contain or prevent the spread of infectious disease. Isolation is one of the most effective biosecurity measures available on a horse property because many equine pathogens spread directly through respiratory aerosols, nasal discharge, or fomites on shared tack and grooming tools.
Standard isolation protocol requires a dedicated stall or paddock at least 30 metres from the main herd, with a separate water supply, dedicated staff handling, and strict hand-washing between horses. New arrivals from sales, shows, or other properties should be isolated for a minimum of 21 days before joining the resident population — a window that covers the incubation period of strangles, equine influenza, and equine herpesvirus. Horses showing signs of respiratory illness, unexplained fever, or neurological change should be isolated immediately while veterinary assessment is arranged. After isolation, shared areas and equipment should be disinfected before re-use. Isolation should be distinguished from simple separation: it implies full infection-control measures, not just physical distance. See also parenteral treatment during the isolation period for parenteral treatment of isolated horses, and the the vaccination programme that isolation reinforces for preventing the most common communicable diseases.