Diagnosis of bovine group A rotavirus, bovine coronavirus, <i>Escherichia</i> <i>coli</i> K99, <i>Cryptosporidium</i> spp., <i>Giardia</i> spp. in calf diarrhea with one-step duplex RT-PCR: histopathological and immunochromotographic methods.

Infections causing diarrhea in cattle breeding pose a substantial threat to calf breeding and health, causing considerable economic losses worldwide, including in Türkiye. The primary causative agents of calf diarrhea include bovine group A rotavirus, bovine coronavirus (BCoV), <i>Escherichia coli</i> K99, <i>Cryptosporidium</i> spp., and <i>Giardia</i> spp. The objective of this study was to diagnose the pathogens present in samples taken from calves exhibiting diarrhea symptoms in the Elaziğ province of Türkiye. The study material consisted of 85 fecal samples from calves up to 30 days of age with diarrhea symptoms and 42 small intestine samples from calves died as a result of diarrhea symptoms after necropsy. Following total RNA isolation from the samples, one-step duplex reverse transcription polymerase chain reaction (RT-PCR) analysis was conducted to identify the bovine rotavirus (BRV) and BCoV. Our results indicated that 24 of the samples were positive for BRV, 13 were positive for BCoV, and 25 were positive for BRV and BCoV in the form of mixed infection. The immunochromatographic analysis revealed that three samples were positive for <i>E. coli</i> K99 antigens, 12 for <i>Cryptosporidium</i> spp. antigens, and 28 for <i>Giardia</i> spp. antigens. Our results indicate that one-step duplex RT-PCR, immunohistochemistry, and immunochromatography methods can be valuable tests to be used in routine diagnostic laboratories for the detection of pathogens associated with calf diarrhea.