Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Ave., Charlottetown, C1A 4P3, Canada.
J Dairy Sci. 2013 Mar;96(3):1568-80. doi: 10.3168/jds.2012-5902. Epub 2013 Jan 16.
The objective of the study was to evaluate the ability of an estimate of the herd intramammary infection (IMI) incidence rate computed using repeated somatic cell count (SCC) measurements (quarter- and composite-SCC; hereafter, the SCC-derived herd IMI incidence, SCCI)to predict the incidence rate computed using repeated quarter-milk bacteriological culture (hereafter, bacteriological culture incidence, BCI) during the lactating period. A cohort of 91 Canadian dairy herds was followed in 2007 and 2008. In each herd and at each of 4 sampling periods, a series of 3 to 7 quarter-milk samples was collected from a sample of 15 cows. Routine milk bacteriological culture was conducted to identify IMI, SCC was measured on the quarter-milk samples, and composite-SCC of the preceding and following dairy herd improvement (DHI) tests were obtained. Mastitis pathogens were grouped in 3 categories: major, minor, and any pathogens. For each herd and for each period, BCI was computed for each group of organisms. Similarly, SCCI were computed using quarter- and DHI composite-SCC and using a threshold of 200,000 cells/mL to define infected quarters or cows. A linear regression model taking into account the structure of the data was used to compare the SCCI to the BCI. A similar model was used to compare fluctuations (i.e., changes from one sampling period to the next) over time of the SCCI and BCI. Measures of correlation between observed and predicted rates were computed and limits of agreement plots sketched to better explore the predictive ability of the SCCI. The quarter-milk SCC measurements that could be obtained-for instance, using on-line milking system measurements-appeared to be particularly valuable. Quarter-SCCI showed a positive and significant association with the BCI. However, limits of agreement plots indicated important disagreement for the small proportion of observations with very high BCI. Quarter-level SCCI and BCI fluctuations were also significantly associated, and a substantial correlation (Spearman rho ranging from 0.54 to 0.58) could be seen between observed and predicted rates. Conversely, the predictive value of composite-DHI SCC for monitoring IMI incidence during the lactation seemed to be quite limited. Composite SCCI was strictly associated with major IMI BCI, showed a relatively low correlation with the observed rate (Spearman rho: 0.14), and was of little help for longitudinal monitoring of the IMI incidence.
本研究旨在评估使用重复体细胞计数（SCC）测量值（ quarters 和 composite-SCC；以下简称 SCC 估算的 herd IMI 发病率，SCCI）估算 herd IMI 发病率的能力，以预测在泌乳期内使用重复 quarter 乳细菌培养（以下简称 bacteriological culture incidence，BCI）估算的 herd IMI 发病率。2007 年和 2008 年，对 91 个加拿大奶牛场进行了队列研究。在每个牛场的 4 个采样期间，从 15 头奶牛中采集了一系列 3 到 7 份 quarter 牛奶样本。对 quarter 牛奶样本进行常规 milk bacteriological culture 以鉴定 IMI，测量 quarter-SCC，并获得前一次和下一次 dairy herd improvement (DHI) 测试的 composite-SCC。乳腺炎病原体分为 3 类：主要病原体、次要病原体和任何病原体。对于每个牛场和每个时期，为每个生物体组计算 BCI。同样，使用 quarter 和 DHI composite-SCC 计算 SCCI，并使用 200,000 个细胞/mL 的阈值来定义感染的 quarters 或奶牛。考虑到数据结构的线性回归模型用于比较 SCCI 和 BCI。使用类似的模型比较 SCCI 和 BCI 随时间的波动（即从一个采样期到下一个采样期的变化）。计算了观察到的和预测到的速率之间的相关性度量，并绘制了协议限图以更好地探索 SCCI 的预测能力。可以获得的 quarter 牛奶 SCC 测量值（例如，使用在线挤奶系统测量值）似乎特别有价值。Quarter-SCCI 与 BCI 呈正相关且具有统计学意义。然而，协议限图表明，对于 BCI 非常高的少数观察值，存在重要的差异。Quarter 水平的 SCCI 和 BCI 波动也呈显著相关，观察到的和预测到的速率之间存在很强的相关性（Spearman rho 范围为 0.54 到 0.58）。相反，复合 DHI SCC 用于监测泌乳期 herd IMI 发病率的预测值似乎相当有限。Composite SCCI 与主要 herd IMI BCI 严格相关，与观察到的速率相关性较低（Spearman rho：0.14），对 herd IMI 发病率的纵向监测几乎没有帮助。
