Bates Andrew, O'Brien Rory, Liggett Simon, Griffin Frank
Vetlife Centre for Dairy Excellence, Vetlife Scientific, 1 Waitohi-Temuka Road, Temuka, 20 Wilson Street, Geraldine, New Zealand.
Disease Research Limited, Invermay Agricultural Centre, Mosgiel, New Zealand.
BMC Vet Res. 2019 Jul 29;15(1):266. doi: 10.1186/s12917-019-2014-6.
Johne's disease is a major production limiting disease of dairy cows caused by infection with Mycobacterium avium subsp. paratuberculosis in calf-hood. The disease is chronic, progressive, contagious and widespread with no treatment and no cure. Economic losses arise from decreased productivity through reduced growth, milk yield, fertility and also capital losses due to premature culling or death. Control chiefly centers upon removing those animals which actively shed bacteria and protecting calves from infection. A prolonged pre-clinical shedding phase, lack of test sensitivity, organism persistence and abundance in the environment as well as management systems that expose susceptible calves to infection make control challenging, particularly in pastoral, seasonal dairy systems. Combining a novel testing strategy to remove infected cows along with limited measures to protect vulnerable calves at pasture, this study reports the successful reduction over a four-year period of seroprevalence of cows testing positive for MAP infection in a New Zealand pastoral dairy herd.
For all age groups considered the apparent seroprevalence of cows testing positive decreased from 297 / 1,122 (26%) in 2013-2014, to 24 / 1,030 (2.3%) in 2016-2017. Over the same period, the apparent seroprevalence in primiparous cows decreased from 39 / 260 (15%) to 7 / 275 (2.5%) and in multiparous cows from 258 / 862 (29.9%) to 17 / 755 (2.3%). The reported proportion of calved cows culled annually from suspected clinical Johne's disease fell from 55 / 1,201 (5%) in the year preceding the control program to 5 / 1,283 (0.4%) in the final year of the study.
On this farm, reduction in the prevalence of infection was achieved by reducing the infectious pressure through targeted culling of heavily shedding animals together with limited measures to protect calves at pasture from exposure to Mycobacterium avium subsp. paratuberculosis. Whilst greater protection of young animals through separation from infected cows and their colostrum and milk would have reduced the risk of neonatal infection, this study demonstrates, in this case, that these management measures while prudent were not essential for effective reduction in the prevalence of MAP infection.
约内氏病是奶牛的一种主要生产限制疾病，由犊牛期感染副结核分枝杆菌引起。该疾病是慢性、渐进性、传染性且广泛传播的，无法治疗和治愈。经济损失源于生长、产奶量、繁殖力下降导致的生产力降低，以及过早淘汰或死亡造成的资本损失。控制主要集中在清除那些积极排菌的动物，并保护犊牛免受感染。临床前排菌期延长、检测敏感性不足、病原体在环境中的持续存在和大量存在，以及使易感犊牛暴露于感染的管理系统，使得控制具有挑战性，尤其是在牧区季节性奶牛养殖系统中。本研究结合一种新型检测策略以清除感染奶牛，并采取有限措施保护牧场中的易感犊牛，报告了在四年时间里成功降低了新西兰一个牧区奶牛群中检测出副结核分枝杆菌感染呈阳性的奶牛的血清阳性率。
对于所有考虑的年龄组，检测呈阳性的奶牛的表观血清阳性率从2013 - 2014年的297/1122（26%）降至2016 - 2017年的24/1030（2.3%）。在同一时期，初产奶牛的表观血清阳性率从39/260（15%）降至7/275（2.5%），经产奶牛从258/862（29.9%）降至17/755（2.3%）。报告的每年因疑似临床约内氏病而被淘汰的产犊奶牛比例从控制计划前一年的55/1201（5%）降至研究最后一年的5/1283（0.4%）。
在这个农场，通过有针对性地淘汰大量排菌动物以降低感染压力，并采取有限措施保护牧场中的犊牛免受副结核分枝杆菌感染，实现了感染率的降低。虽然通过将幼畜与感染奶牛及其初乳和牛奶隔离可以更好地保护幼畜，从而降低新生犊牛感染的风险，但本研究表明，在这种情况下，这些管理措施虽然谨慎，但对于有效降低副结核分枝杆菌感染率并非必不可少。
