Causative agents and epidemiology of diarrhea in Korean native calves

Lee, Sung-Hwan; Kim, Ha-Young; Choi, Eun Wha; Kim, Doo

A previous study conducted in the Gyeongnam province of Korea reported that the prevalence of diarrhea was 31.3% in spring, 28.5% in summer, 24.9% in fall, and 15.3% in winter [22] . In the present study, the prevalence of diarrhea was 46.3% in spring, 13.4% in summer, 7.9% in fall, and 32.3% in winter. Spring was the most dangerous season because the morbidity and mortality rates associated with diarrhea in diarrheal calves were the highest in this season. A previous study in south-west France reported that the month of birth was significantly associated with morbidity: The highest morbidity rates were observed in December and March, and the mortality rate was two times higher in December than in other months [6] . In the present study, the incidence of calf diarrhea increased in proportion to the number of calf births in spring. In summer and fall, the incidence of diarrhea decreased in proportion to the number of calf births. In winter, however, the ratio of diarrheal calves to calf births was doubled. As the number of calf births in spring is the highest, diarrhea occurs more frequently owing to changes in temperature and the increased chance of contact with causative agents of calf diarrhea. In winter, few calf births were reported, but the calves appeared to be more exposed to causative agents and diarrhea. These infections became more severe, owing to the decreased resistance of calves upon exposure to the cold weather. The reason underlying the increase in mortality and morbidity was associated with the rotaviral infection of calves. Rotavirus-associated mortality was the highest component (46.7%) of total mortality. This observation is consistent with the most frequent rotavirus infection within 1 week of age, especially in spring and winter. In general, viruses tend to be more stable during the cold season, presumably owing to low temperatures. The prevalence of diarrhea caused by rotavirus was significantly different between seasons.