The study is focused on the proposal of preventive measures against the occurrence of calf diarrheal diseases during the milk feeding period. A four-year follow-up of the causative agents of diarrhoea was carried out in 981 calves during the milk feeding period housed in outdoor individual hutches under an all-in and all-out system and in a shelter under a continuous flow system. Preventive measures against the occurrence of diarrheal diseases should be aimed at limiting the occurrence of pathogens in and at increasing the level of passive (colostral) and active (post-vaccination) immunity of calves.