John Emily E, Nekouei Omid, McClure J T, Cameron Marguerite, Keefe Greg, Stryhn Henrik
Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Ave, Charlottetown, PE, C1A 4P3, Canada.
Prev Vet Med. 2018 Jun 1;154:90-94. doi: 10.1016/j.prevetmed.2018.03.015. Epub 2018 Mar 21.
Bulk tank milk (BTM) samples are used to determine the infection status and estimate dairy herd prevalence for bovine leukaemia virus (BLV) using an antibody ELISA assay. BLV ELISA variability between samples from the same herd or from different herds has not been investigated over long time periods. The main objective of this study was to determine the within-herd and between-herd variability of a BTM BLV ELISA assay over 1-month, 3-month, and 3-year sampling intervals. All of the Canadian Maritime region dairy herds (n = 523) that were active in 2013 and 2016 were included (83.9% and 86.9% of total herds in 2013 and 2016, respectively). BLV antibody levels were measured in three BTM samples collected at 1-month intervals in early 2013 as well as two BTM samples collected over a 3-month interval in early 2016. Random-effects models, with fixed effects for sample replicate and province and random effects for herd, were used to estimate the variability between BTM samples from the same herd and between herds for 1-month, 3-month, and 3-year sampling intervals. The majority of variability of BTM BLV ELISA results was seen between herds (1-month, 6.792 ± 0.533; 3-month, 7.806 ± 0.652; 3-year, 6.222 ± 0.528). Unexplained variance between samples from the same herd, on square-root scale, was greatest for the 3-year (0.976 ± 0.104), followed by the 1-month (0.611 ± 0.035) then the 3-month (0.557 ± 0.071) intervals. Variability of BTM antibody levels within the same herd was present but was much smaller than the variability between herds, and was greatest for the 3-year sampling interval. The 3-month sampling interval resulted in the least variability and is appropriate to use for estimating the baseline level of within-herd prevalence for BLV control programs. Knowledge of the baseline variability and within-herd prevalence can help to determine effectiveness of control programs when BTM sampling is repeated at longer intervals.
使用抗体酶联免疫吸附测定法（ELISA），通过大容量储槽奶（BTM）样本确定感染状态并估计牛白血病病毒（BLV）在奶牛群中的流行率。尚未对来自同一牛群或不同牛群的样本之间的BLV ELISA变异性进行长期调查。本研究的主要目的是确定在1个月、3个月和3年的采样间隔内，BTM BLV ELISA检测在牛群内和牛群间的变异性。纳入了2013年和2016年活跃的加拿大沿海地区所有奶牛群（n = 523）（分别占2013年和2016年总牛群的83.9%和86.9%）。在2013年初每隔1个月采集的3份BTM样本以及2016年初在3个月间隔内采集的2份BTM样本中测量了BLV抗体水平。采用随机效应模型，样本重复和省份为固定效应，牛群为随机效应，以估计在1个月、3个月和3年采样间隔内来自同一牛群和不同牛群的BTM样本之间的变异性。BTM BLV ELISA结果的大部分变异性出现在不同牛群之间（1个月时为6.792±0.533；3个月时为7.806±0.652；3年时为6.222±0.528）。在平方根尺度上，同一牛群样本之间无法解释的方差在3年时最大（0.976±0.104），其次是1个月时（0.611±0.035），然后是3个月时（0.557±0.071）。同一牛群内BTM抗体水平存在变异性，但远小于不同牛群间的变异性，且在3年采样间隔时最大。3个月的采样间隔导致的变异性最小，适用于估计BLV控制计划中牛群内流行率的基线水平。当以较长间隔重复进行BTM采样时，了解基线变异性和牛群内流行率有助于确定控制计划的有效性。
