Equine adenovirus type 1 (EAdV1) appears as a subclinical infection in most immunocompetent foals and horses.However,there is serologic evdence of widespread infection in equine population in numerous different countries around the world.It causes mild,upper respiratory tract (URT) disease in normal foals but has caused acute URT disease, as well as follicular conjunctivitis in foals that have been experimentally infected.One of these foals was specific-pathogen-free (SPF) and colostrum-deprive but immunocompetent at 6 weeks of age;the orther foal was younger,had received colostrum, and sustained deceeased clinical signs,despite its age (4 day).Equine adenovirus type I is the dominant pathogen in Arabian foals have a profressive EAdV1 bronchopneumonia, as well as EAdV1-related pathology in many other organs and tissues.