When is the best time to test paratuberculosis positivity? Observations from a follow-up study in Hungarian dairy herds

Barbara Vass-Bognár¹Mikolt Bakony^2*Kinga Fornyos³Walter Baumgartner⁴Johannes Khol⁴Viktor Jurkovich¹

• ¹University of Veterinary Medicine Budapest, Budapest, Hungary
• ²Semmelweis University, Budapest, Hungary
• ³Eurofins Vet-Controll Ltd., Budapest, Hungary
• ⁴University of Veterinary Medicine Vienna, Vienna, Vienna, Austria

The objective of the present study was to find the most practical combination of diagnostic procedures and time points during lactation to identify MAP-infected animals. Four Hungarian dairy farms with a 4-5% apparent MAP positivity were enrolled in the study. Of these herds, 52 non-lactating, known MAP-positive pregnant dairy cows (13 animals from each farm) were chosen for the study three weeks before their expected calving. We collected individual feces, blood, and milk samples from these focal cows six times, at 1-5, 10-14, 40-60, 90-120, 180-200, and 280-300 days in milk (DIM). The optimal time for sampling using serum ELISA was between DIM 40-60.Regarding fecal qPCR, the best sampling time was between DIM 10-14 or DIM 40-60, according to the results of the present study. Among the methods, qPCR proved the most reliable testing method during the study. ELISA S/P values correlated with the fecal qPCR Ct values, with serum ELISA slightly more sensitive than milk ELISA. We found the most suitable period for this to be 40-60 days after calving, before insemination, which can later be the basis for a culling decision.Animals later developing clinical symptoms showed distinctively different test positivity and biomarker patterns from the onset of lactation, compared to animals not developing clinical symptoms in the observation period.