Determining the cause of diarrhea in pre-weaning calves
Alexis Thompson, DVM, PhD
Pre-weaning calf diarrhea is a common concern in the beef and dairy industry and the cause may be difficult to determine. This is due to the multifactorial nature of calf diarrhea. Multiple etiologies, both infectious and non-infectious, can result in diarrhea. Disease is caused by an interaction between a host, an agent, and the environment (Figure 1). This is commonly referred to as the epidemiological triad.
When discussing the cause of calf diarrhea, most people instantly think of infectious etiology. Rotavirus, coronavirus, E. coli, Salmonella, and Cryptosporidium can all cause diarrhea in neonatal calves. Most of these pathogens have a typical timeline for when they cause disease, such as Salmonella which usually affects calves between 5 and 14 days of life. However, these organisms can be found in the feces of healthy as well as diseased calves. Generally, for diarrhea, an infectious etiology is a necessary component of the disease process, but it is not sufficient alone.
In the host (calf), anything that causes immunosuppression or immunodeficiency can contribute to disease development. Neonatal calves that did not consume an adequate amount of maternal antibodies are commonly referred to as having failed transfer of passive immunity and are at greater risk of disease. However, calves that consume adequate maternal antibodies can also be at risk of disease if there is sufficient exposure to a pathogen or are environmental factors that contribute to the disease process. This is because colostrum consumption and the transfer of maternal antibodies are not fully adequate to prevent disease.
Environmental contributors to calf diarrhea tend to focus on milk management (in dairy herds) and cleanliness. High stocking densities or poor environmental conditions (rain, mud) can increase a calf’s risk for developing neonatal diarrhea. Milk with high osmolality (> 500 mOsm/kg) can damage the lining of the gastrointestinal tract which can also lead to diarrhea. Inconsistent feeding times and milk temperatures, ideally between 101.0 and 102.5 F, can contribute to diarrhea. These factors increase a calf’s risk for diarrhea but alone, are not sufficient.
Host, agent, and environmental factors by themselves are not sufficient to cause diarrhea but when combined, they can (Figure 2). For example, a calf is receiving a milk replacer at a low temperature (environment). This causes hypomotility of the intestine (host) and proliferation of E. coli (agent) resulting in diarrhea. Independently, low temperature milk and E. coli would not result in diarrhea. However, together with the calf’s physiologic response, the calf develops diarrhea.
Most causes of calf diarrhea are neither necessary nor sufficient to cause disease as there are multiple ways for disease to develop. The component cause of calf diarrhea complicates diagnostic testing as most tests focus on identifying infectious etiologies. Therefore, when evaluating operations with calf diarrhea, it is important to consider the calf and environmental factors that contribute to disease development. Identifying which component contributes the most to disease will aid in treatment, prevention, and management.
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