Faculty of Agricultural Sciences, Department of Animal Health and Bioscience, University of Aarhus, Blichers Allé 20, PO Box 50, DK-8830 Tjele, Denmark.
J Dairy Sci. 2011 Aug;94(8):3824-34. doi: 10.3168/jds.2010-3933.
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.
通过模拟，确定了淘汰感染禽分枝杆菌副结核亚种（Mycobacterium avium ssp. paratuberculosis）奶牛的时间对流行率和盈利能力的影响。七种不同的检测和淘汰策略与无控制策略（1）和无感染途径控制及无淘汰策略（2）进行了比较。在一个具有典型繁殖管理（发情检测率为 38%）的牛群中，评估了对真实流行率和毛利润的影响。在繁殖管理较差（发情检测率为 28%）的牛群中重复了该研究，因为较差的繁殖会导致缺乏替代动物，据推测这会影响淘汰的经济效益。还评估了牛奶、后备母牛和小时工资价格的变化对结果的影响。模拟结果表明，在首次阳性抗体 ELISA 检测后立即淘汰是降低流行率的最有效淘汰策略。然而，关闭传播途径在降低流行率方面更为有效。在最初的 3 至 6 年内，所有的检测和淘汰策略每年使每头牛舍的毛利润减少 5 至 55 美元。这些损失在第 6 至 19 年通过增加的毛利润得到了完全补偿。在短期内（繁殖正常的 7 年和繁殖不正常的 10 年），当产奶量根据胎次和泌乳阶段下降到预期值的 85%以下时，淘汰阳性奶牛是最有利可图的，尤其是在繁殖管理较差的牛群中。然而，这种策略只能稳定流行率，而不能降低它。从实施策略的长期来看（>7 年），最有利可图的策略是在首次检测呈阳性后立即或尽快淘汰奶牛。牛奶价格的变化并没有影响不同淘汰策略之间的排名。后备母牛的市场价格（20%）增加使所有淘汰策略的利润降低，并且使基于产奶量标准的淘汰策略在较长时间内（11 至 13 年）成为最有利可图的淘汰策略。后备母牛价格降低 20%使在繁殖正常的牛群中首次检测呈阳性后立即淘汰成为总体上最有利可图的策略，而在繁殖不正常的牛群中，这一策略在 9 年后才成为最有利可图的策略。总之，理想的淘汰策略取决于干预的目的、时间范围以及繁殖能力与替代动物价格的结合。
