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. 2025 Jun 19:12:1570915.
doi: 10.3389/fvets.2025.1570915. eCollection 2025.

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

Barbara Vass-Bognár  1 , Mikolt Bakony  2 , Kinga Fornyos  3 , Walter Baumgartner  4 , Johannes Lorenz Khol  4 , Viktor Jurkovich  5
Affiliations

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

Barbara Vass-Bognár et al. Front Vet Sci. .

Abstract

The objective of the present study was to find the most practical combination of diagnostic procedures and time points during lactation to identify Mycobacterium avium ssp. paratuberculosis (MAP)-infected animals. Four Hungarian dairy farms with a 4-5% apparent MAP positivity were enrolled in the study, and 13 non-lactating, known MAP-positive pregnant cows were chosen from each farm. Feces, blood, and milk samples were collected from each cow at 1-5, 10-14, 40-60, 90-120, 180-200, and 280-300 days in milk (DIM) and ELISA and PCR assays were performed for antibody or pathogen detection. Animals that later developed clinical paratuberculosis symptoms showed distinctly different patterns of test positivity than those that did not develop clinical symptoms during the observation period. The optimal time for detecting MAP-positive animals with the highest probability was DIM 40-60 with serum ELISA and DIM 10-14 and 40-60 for PCR assays, respectively. Serum ELISA proved to be slightly more sensitive than milk ELISA. S/P values showed a moderate correlation with the fecal qPCR Ct values. We found that the most suitable period for MAP screening is 40-60 days after calving.

Keywords: ELISA; dairy cow; paratuberculosis; qPCR; sampling time.

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Conflict of interest statement

KF was employed by Eurofins Vet-Controll Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Boxplot of MAP-serum ELISA outcomes for animals culled and not culled between 60–90 DIM and sampling interval. Asterisks indicate significant differences between group medians (p < 0.001). The dashed line indicates the threshold for ELISA positivity in serum. MAP, Mycobacterium avium subsp. paratuberculosis; DIM, days in milk.
Figure 2
Figure 2
Boxplot of MAP-milk ELISA outcomes for animals culled and not culled between 60–90 DIM and sampling interval. Asterisks indicate significant differences between group medians (p < 0.001). The dashed line indicates the threshold for ELISA positivity in milk. MAP, Mycobacterium avium subsp. paratuberculosis; DIM, days in milk.
Figure 3
Figure 3
Boxplot of MAP-fecal Ct values for animals culled and not culled between 60–90 DIM and sampling interval. Asterisks indicate significant differences between group medians (p < 0.001). The dashed line indicates the threshold for qPCR Ct positivity in feces. MAP, Mycobacterium avium subsp. paratuberculosis; Ct, cycle threshold; DIM, days in milk.
Figure 4
Figure 4
Mean body condition scores of animals culled and not culled between 60 and 90 DIM according to the sampling interval. Error bars represent standard error. Asterisks indicate significant differences between groups (p < 0.001). For better interpretation, means are displayed, however, tests were performed on medians.
Figure 5
Figure 5
Mean fecal scores of animals culled and not culled between 60 and 90 DIM according to the sampling interval. Error bars represent standard error. Asterisks indicate significant differences between groups (p < 0.001). For better interpretation, means are displayed, however, tests were performed on medians.
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