Strategies for time of culling in control of paratuberculosis in dairy herds.

Effect of time for culling cows infected with Mycobacterium avium ssp. paratuberculosis on prevalence and profitability was identified through simulations. Seven test-and-cull strategies with different culling criteria and no attempts to close infection routes were compared with strategies with (1) no control and (2) closure of infection routes and no culling. The effects on true prevalence and gross margin were evaluated in a herd with typical reproduction management (heat detection rate of 38%). This was repeated in a herd with poor reproduction management (heat detection rate of 28%), because poor reproduction leads to lack of replacement animals, which was hypothesized to affect the economic effects of culling. Effects of varying prices of milk, replacement heifers, and hourly wages were also evaluated. The simulated results predicted that immediate culling after the first positive antibody ELISA test would be the most effective culling strategy to reduce prevalence. However, closing transmission routes was even more effective in reducing the prevalence. In the first 3 to 6 yr, all test-and-cull strategies reduced gross margin by US$5 to 55/stall per year. These losses were fully compensated by increased gross margin in yr 6 to 19. In the short run (7 yr with typical reproduction and 10 yr with poor reproduction), it was most profitable to cull test-positive cows when their milk yield decreased below 85% of that expected according to their parity and lactation stage, especially in herds with poor reproduction management. However, this strategy only stabilized the prevalence and did not reduce it. In the long term (>7 yr from implementation of a strategy), it was most profitable to cull cows immediately or as soon as possible after testing positive the first time. Varying milk prices did not affect the ranking between the different culling strategies. Increased market price (20%) of replacement heifers made all culling strategies less profitable and made culling based on a milk yield criterion the most profitable culling strategy for a longer period (11 to 13 yr). A 20% reduction in heifer price made immediate culling after a positive test the most profitable strategy overall in herds with typical reproduction, and after 9 yr in herd with poor reproduction. To conclude, the ideal culling strategy depends on the aim of intervention, the time horizon, and the reproductive capabilities combined with prices of replacement animals.

Kudahl AB ，Nielsen SS ，Ostergaard S 《-》

Simulated economic effects of improving the sensitivity of a diagnostic test in paratuberculosis control.

Kudahl AB ，Sørensen JT ，Nielsen SS ，Ostergaard S ... -  《PREVENTIVE VETERINARY MEDICINE》

Economy, efficacy, and feasibility of a risk-based control program against paratuberculosis.

Kudahl AB ，Nielsen SS ，Østergaard S 《-》

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.

Collins MT ，Eggleston V ，Manning EJ 《-》

Evaluation of test-strategies for estimating probability of low prevalence of paratuberculosis in Danish dairy herds.

Sergeant ES ，Nielsen SS ，Toft N 《PREVENTIVE VETERINARY MEDICINE》