An overview of calf diarrhea - infectious etiology, diagnosis, and intervention

Cho, Yong-il; Yoon, Kyoung-Jin

Harsh weather conditions such as low temperatures, rain, heavy snow, wind, and high levels of moisture act as stress factors to young calves and increase the susceptibility of calves to diarrhea [13, 71] . Neonatal calves are not able to effectively regulate their body temperature when exposed to extreme weather conditions. This may induce hypothermia or hyperthermia resulting in immune system impairment. The dam is less influenced by environmental stress than the calf. However, the probability of dystocia or metabolic disease is still increased by environmental stress [89] . Special care is required to reduce environmental risk factors closely associated with calving season including the provision of dry, draft-free shelter. The calving season can be adjusted to a time when environmental conditions are more favorable by implementing a controlled breeding program. Exposure to a contaminated environment is the main cause of calf diarrhea. A simple solution would be to reduce the pathogen load into the environment where calves are raised although this has always been a challenge for cattle producers. After birth, calves are directly exposed to contaminated environments which can be influenced by various factors such as the presence of infected animals, overcrowding, concurrent cow-heifercalving, contaminated calving lots, and a lack of calf segregation by age [71, 72] . These factors usually work synergistically and increase the opportunity for increased duration of exposure to a higher quantity of pathogens. Conversely, intervention for preventing calf diarrhea is focused on the control and reduction of each factor (e.g., pathogen load and environment contamination). The basic concepts of intervention for reducing the incidence of calf diarrhea are based on 1) decreasing pathogen exposure by planning to breed and heifers first calving, which reduces the exposure of more susceptible newborn calves to pathogens, 2) reducing pathogen loading into the environment by shortening the calving season through scheduling breeding, which reduces the period of pathogen entry into the environment; and 3) keeping a clean area (or pathogen-free area) by grouping animals according to their calving date so that the calving area can be kept clean after occupation by the previous calving group. The Sandhills Calving System has been reported to be highly effective for controlling calf diarrhea caused by multiple pathogens [126] . The system is based on preventing pathogen exposure during the early stage by segregating groups of calves in the order of calving time and maintaining a clean calving area. Essentially, a group of cows is moved into the first calving pasture when calving begins and calving continues in the first pasture for 2 weeks. Cows that have not yet calved by the end of the second week are moved to a second pasture where calving continues for 1 week. Any remaining cows that have not calved are moved to the third pasture where calving continues for another week. Finally, calves born in different pastures are grouped together when the youngest calves are 4 weeks old. The calving interval in each pasture area can vary depending upon herd size, available pasture, and previous history of calf diarrhea for each farm. Although the Sandhills Calving System was initially introduced for pasturing calving cows, the concept is applicable for dry lot calving depending upon the situation of each farm. For example, when the pasture area is not large enough