Successful control of Johne's disease in nine dairy herds: results of a six-year field trial.

The objective was to evaluate if a standardized Johne's disease control program significantly reduced the prevalence of cattle infected with Mycobacterium avium ssp. paratuberculosis in dairy herds with a moderate to high initial infection prevalence of >or=10% ELISA-positive adult cattle. Nine Wisconsin dairy herds of diverse sizes and management styles completed the 6-yr study. The control program involved changes to heifer rearing practices in combination with a routine testing program. For heifers, the program specifically required 1) segregated maternity pens for ELISA-positive and ELISA-negative cattle; 2) removal of calves from the maternity pen in <2h; 3) use of colostrum only from individual ELISA-negative cows (no colostrum pooling); 4) hygienic collection of colostrum; 5) feeding of pasteurized milk as milk replacer or on-farm pasteurized milk until weaning; and 6) minimizing contact with manure from the adult cattle until weaning. The testing program was designed to detect the most infectious cattle by using a commercial ELISA once on every adult during each lactation. Producers were required to cull cows with strong-positive ELISA results before the next calving and to label cows with low- to medium-level ELISA results and manage them to limit infection transmission. Outcomes were measured by comparing the apparent prevalence based on ELISA or fecal culture in the whole herd and in first-lactation cohorts at 2 time points: before implementation of the control program and at the end of the trial. The combined results from the 9 herds showed a significant reduction in ELISA-positive cows, from 11.6% at the start of the trial to 5.6% at conclusion of the trial. The apparent prevalence decline among first-lactation cows was greater and was evident by ELISA (10.4 vs. 3.0%) and by fecal culture (17.0 vs. 9.5%). Although variations among farms were observed, the collective results demonstrated that bovine paratuberculosis can be controlled in dairy herds through effective heifer husbandry practices in combination with diagnostic testing to identify, for culling or management, cows most likely infectious.