ISSUE FOCUS FEED & ADDITIVE MAGAZINE November 2025 39 BACTERIA PROTOZOA VIRUSES Rotavirus Coronavirus Bovine Viral Diarrhea Virus Bovine Herpesvirus I Cryptosporidia Coccidia E. coli Salmonella Clostridium perfringens There are numerous infectious and non-infectious agents associated with calf diarrhea—it is not a single disease. Infectious causes include bacteria such as E. coli, Salmonella, and Clostridium perfringens; viruses such as rotavirus and coronavirus; and protozoa such as cryptosporidia and coccidia (Figure 2). Some pathogens, like E. coli, produce toxins that stimulate an enzyme cascade and a large release of chloride ions into the intestinal lumen. Sodium passively follows to help maintain electron neutrality, and, as the osmotic pressure in the intestine increases, so does water. This is the pathogenesis of secretory diarrhea. Other pathogens—typically rotavirus and coronaviruses—cause osmotic diarrhea. These pathogens attack the intestinal villi causing villus atrophy, reducing the intestine’s digestive and absorptive capacity. Unabsorbed nutrients then remain in the Figure 1. The many factors associated with the health and morbidity of calves Birth Weight Pathogen Pressure Housing Conditions Ventilation Serum IgG Levels Feeding Strategy Health Management Ambient Temperatures Figure 2. The most common bacteria responsible for calf diarrhea are E. Coli, Salmonella, and Clostridium perfringens. The viruses causing diarrhea in the calf are Rotavirus, Coronavirus, Bovine Viral Diarrhea Virus, and Bovine Herpesvirus 1. A few protozoan species like Cryptosporidia and coccidiosis are responsible for calf diarrhea.
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