Individual faecal and boot swab sampling to determine John's disease status in small cattle herds.

Individual faecal samples were collected from adult animals in 275 cattle farms previously positive for Mycobacterium avium subsp. paratuberculosis (MAP). In addition, boot swab samples were collected in 30 randomly chosen farms. Faecal samples were tested for MAP by a combination of bacterial culture and PCR. A logistic regression and the Pearson Correlation were used to calculate the relation between the number of MAP‑positive cows and boot swab results. In 66.9% of all previously tested herds, no positive individual faecal sample was detected, indicating possible fadeout of the infection. In 9 (30.0%) of the 30 selected farms, at least one MAP‑shedding animal was detected in faecal samples individually collected, while only 5 (16.7%) of these farms were found positive when the boot sampling method was used. The sensitivity of the boot swab sampling increased up to 92% (95% CI: 41%‑99%), if at least 12 animals were faecal MAP‑shedders in a herd. The current study shows possible fadeout of JD in a substantial percentage of previously infected herds. Furthermore, in small herds, a relatively high within‑herd prevalence of MAP‑shedding animals is needed to assure reliable positive boot swab results.