The reference population consisted of 75 Spanish Holstein cows from a single farm located in the Basque Country. In 2022, only five cows from this herd had an ELISA positive result and all the animals had a negative fecal PCR result. Only adult cows (2 years or older, 4.5 years mean age) were included in the study. All the animals included in this study were registered with the Spanish Federation of Holstein cattle (CONAFE; www.conafe.com.) and had negative fecal PCR results when blood samples were collected and in subsequent annual samplings. In addition, the animals used in this study were not diagnosed with any other pathogen. Blood samples were collected in groups of 16 per sampling day. The validation population consisted of 16 cows from the same farm.
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