Digital dermatitis or Mortellaro’s disease is a highly prevalent bovine dermatological disordersituated in the foot region that causes lameness and impairs animal welfare.In this first part of a twin paper, the role of genetics, immunity, bacteria and hygiene in thedevelopment of this complex disease are described. There is still no consensus regarding the roleof the immune system and the typically isolated Treponema spp. in the pathogenesis of digitaldermatitis. Moisture and dirt are undoubtedly important for disease transmission in and betweendairy farms; furthermore, the genetic component of the disease will be more deeply discussed.