A national control program against bovine respiratory syncytial virus (BRSV) and bovine coronavirus (BCV) was launched in Norway in 2016. A key strategy in the program is to test for presence of antibodies and protect test-negative herds from infection. Because these viruses are endemic, the rate of re-introduction can be high, and a disease-free status will become more uncertain as time from testing elapses. The aim of this study was to estimate the probability of freedom (PostPFree) from BRSV and BCV antibodies over time by use of bulk tank milk (BTM) antibody-testing, geographic information and animal movement data, and to validate the herd-level estimates against subsequent BTM testing. BTM samples were collected from 1148 study herds in West Norway in 2013 and 2016, and these were analyzed for BRSV and BCV antibodies. PostPFree was calculated for herds that were negative in 2013/2014, and updated periodically with new probabilities every three months. Input variables were test sensitivity, the probability of introduction through animal purchase and local transmission. Probability of introduction through animal purchase was calculated by using real animal movement data and herd prevalence in the region of the source herd. The PostPFree from the final three months in 2015 was compared to BTM test results from March 2016 using a Wilcoxon Rank Sum Test. The probability of freedom was generally high for test-negative herds immediately after testing, reflecting the high sensitivity of the tests. It did however, decrease with time since testing, and was greatly affected by purchase of livestock. When comparing the median PostPFree for the final three months to the test results in 2016, it was significantly lower (p < 0.01) for test positive herds. Furthermore, there was a large difference in the proportion of test positive herds between the first and fourth quartile of PostPFree. The results show that PostPFree provides a better estimate of herd-level BTM status for both BRSV and BCV than what can be achieved by relying solely on the previous test-result.

中文翻译：

---

在挪威控制计划中，牛呼吸道合胞病毒和牛冠状病毒的疾病自由可能性的畜群水平估计。

2016年在挪威启动了一项针对牛呼吸道合胞病毒（BRSV）和牛冠状病毒（BCV）的国家控制计划。该计划的关键策略是测试抗体的存在并保护测试阴性人群免受感染。由于这些病毒是地方性病毒，因此重新引入的速度可能很高，并且随着测试时间的流逝，无病状态将变得更加不确定。这项研究的目的是通过使用大罐牛奶（BTM）抗体测试，地理信息和动物运动数据来估计BRSV和BCV抗体随时间的自由概率（PostPFree），并验证牛群水平的估计反对随后的BTM测试。在2013年和2016年从西挪威的1148个研究人群中收集了BTM样本，并对它们进行了BRSV和BCV抗体分析。PostPFree是针对2013/2014年阴性的牛群计算的，并每三个月定期更新一次新概率。输入变量是测试敏感性，通过动物购买和局部传播引入的可能性。通过使用真实的动物运动数据和源畜群区域中的畜群流行率，计算了通过购买动物引入的概率。使用Wilcoxon Rank Sum Test将2015年最后三个月的PostPFree与2016年3月以来的BTM测试结果进行了比较。测试后立即呈阴性的牛群的自由可能性通常很高，这反映了测试的高度敏感性。但是，自测试以来，它确实随着时间而减少，并且受牲畜购买的影响很大。将最后三个月的PostPFree中位数与2016年的测试结果进行比较时，测试阳性人群的中位数PostPFree显着较低（p <0.01）。此外，PostPFree的第一个和第四个四分位数之间的测试阳性人群比例存在很大差异。结果表明，与仅依靠先前的测试结果无法实现的结果相比，PostPFree对BRSV和BCV的畜群级BTM状态提供了更好的估计。