Environmental sampling is an effective method for estimating regional dairy herd-level prevalence of infection with Mycobacterium avium ssp. paratuberculosis (MAP). However, factors affecting prevalence estimates based on environmental samples are not known. The objective was to determine whether odds of environmental samples collected on farm changed culture status over 2 sampling times and if changes were specific for location and type of housing (freestall, tiestall, or loose housing), the sample collected (i.e., manure of lactating, dry, or sick cows; namely, cow group), and effects of herd size. In 2012–2013 [sampling 1 (S1)] and 2015–2017 [sampling 2 (S2)], 6 environmental samples were collected and cultured for MAP from all 167 (99%) and 160 (95%) farms, respectively, in the province of Saskatchewan, Canada. Only the 148 dairy farms sampled at both sampling periods were included in the analysis. A mixed effects logistic regression was used to determine whether differences between sampling periods were associated with herd size and sample characteristics (cow group contributing to environmental sample, type of housing, and location). In S1 and S2, 55 and 34%, respectively, of farms had at least 1 MAP-positive environmental sample. Correcting for sensitivity of environmental sampling, estimated true prevalence in S1 and S2 was 79 and 48%, respectively. Herds with >200 cows were more often MAP-positive than herds with <51 cows in both S1 and S2. The percentage of positive samples was lower in S2 compared with S1 for all sampled areas, cow groups contributing to samples, types of housing where samples were collected, and herd size categories. However, samples collected from dry cow areas had the largest decrease in MAP-positive samples in S2 compared with all other cow group samples. Herds that were MAP-negative in S1 with a herd size 51 to 100 or 101 to 150 were more likely to stay MAP-negative, whereas MAP-positive herds with >200 cows more frequently stayed MAP-positive. No difference was observed in the odds of a sample being MAP-positive among housing types or location of sample collection in both sample periods. Of all farms sampled, 104 (70%) did not change status from S1 to S2. In conclusion, when herd-level MAP prevalence decreased over the 3-yr interval, the change in prevalence differed among herd size categories and was larger in samples from dry cow areas. It was, however, not specific to other characteristics of environmental samples collected.

环境采样是估算禽鸟分枝杆菌ssp感染的区域奶牛群水平患病率的有效方法。副结核病（地图）。但是，尚不清楚影响基于环境样本的流行度估计的因素。目的是确定农场中采集的环境样品的几率是否在2个采样时间内改变了养殖状况，以及是否特定于住房的位置和类型（速冻，平摊或散装住房）的变化，所采集的样品（即泌乳粪便） ，干燥或患病的母牛；即母牛群），以及牛群大小的影响。在2012–2013 [采样1（S1）]和2015–2017 [采样2（S2）]中，分别从167个（99％）和160（95％）个农场的6个环境样品中进行了MAP培养。加拿大萨斯喀彻温省。分析中仅包括在两个采样期间采样的148个奶牛场。使用混合效应逻辑回归来确定采样期间之间的差异是否与牛群的大小和样本特征（牛群对环境样本，房屋类型和位置的影响）有关。在S1和S2中，分别有55％和34％的农场至少有1个MAP阳性环境样品。校正环境采样的敏感性，估计的S1和S2的真实患病率分别为79％和48％。在S1和S2中，> 200头母牛的牛群比<51头母牛的牛群MAP阳性率更高。在S2中，在所有采样区域中，S2中阳性样本的百分比均低于S1，构成样本的奶牛群体，收集样本的房屋类型以及畜群大小类别均低于S1。然而，与所有其他奶牛组样品相比，从干旱奶牛地区收集的样品在S2中的MAP阳性样品下降幅度最大。在S1中MAP阴性的牛群，其牛群大小为51至100或101至150，更可能保持MAP阴性，而具有200多头母牛的MAP阳性牛群则更常保持MAP阳性。在两个样本期间内，住房类型或样本收集地点之间样本MAP阳性的几率均未观察到差异。在所有采样农场中，有104个（70％）没有将状态从S1更改为S2。总之，当牧群水平MAP患病率在3年间隔内下降时，患病率变化在不同的牧群规模类别中会有所不同，而在来自干旱奶牛地区的样本中则更大。但是，它并非特定于所收集环境样品的其他特征。