Department of Animal Biosciences, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
Department of Population Medicine, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
J Dairy Sci. 2019 Sep;102(9):8417-8422. doi: 10.3168/jds.2018-16070. Epub 2019 Jul 10.
The objective of this study was to evaluate the accuracy of inline milk fat-to-protein (F:P) data to detect hyperketonemia (HYK) in herds with automated milking systems (AMS). The F:P ratio has been investigated as a tool for detecting HYK with moderate accuracy in past studies, but inline F:P data in AMS may also be useful for HYK screening. To assess the accuracy of these data in commercial settings, we monitored 484 cows from 9 AMS herds for their first 3 wk of lactation, taking blood samples once per week (n = 1,427). Positive cases of HYK were defined by whole-blood β-hydroxybutyrate (BHB) concentrations ≥1.2 or ≥1.4 mmol/L. Milk data were collected from the AMS software on each farm for each cow and converted into 4 different F:P values: (1) value from the same day as the BHB test; (2) 5-d centered-moving average (CMA); (3) 5-d backward-moving average (BMA); (4) 5-d forward-moving average (FMA). In linear regression models, all 4 values were associated with BHB, but slope estimates varied and R were low: same day (slope = 0.95, R = 0.07), CMA (slope = 1.05, R = 0.07), BMA (slope = 0.65, R = 0.04), and FMA (slope = 1.23, R = 0.09). In logistic regression models, the odds of having HYK (BHB ≥1.2 mmol/L) increased with every 0.1-unit increase from the mean F:P ratio (1.16) using same-day values (odds ratio = 1.35, 95% confidence interval = 1.25-1.47) and CMA (odds ratio = 1.39, 95% confidence interval = 1.27-1.51). The same increase in F:P from mean BMA (1.14) and FMA (1.17) was associated with 1.22 and 1.49 times the odds of HYK, respectively. For all 4 F:P variations, we evaluated the sensitivity, specificity, positive predictive value, and negative predictive value of different F:P thresholds with HYK status. As the F:P threshold increased from 1.17 to 1.50, sensitivity decreased (range: 77 to 9%) but specificity increased (range: 58 to 96%). Same-day and CMA F:P cutoffs at which a balance was reached between sensitivity and specificity ranged from 1.18 to 1.22; however, even at these values we found high rates of false positives and negatives (range: 31-39%). These results suggest that inline milk F:P data from inconsistently calibrated sensors should not be used alone to detect HYK in AMS herds.
本研究旨在评估在线乳脂-蛋白（F:P）数据在具有自动化挤奶系统（AMS）的牛群中检测酮血症（HYK）的准确性。过去的研究已经将 F:P 比值作为一种检测 HYK 的工具进行了研究，但其在 AMS 中的在线 F:P 数据也可能有助于 HYK 筛查。为了评估这些数据在商业环境中的准确性，我们在 9 个 AMS 牛群中监测了 484 头奶牛的前 3 周泌乳期，每周采集一次血样（n = 1427）。HYK 的阳性病例定义为全血 β-羟丁酸（BHB）浓度≥1.2 或≥1.4mmol/L。每头奶牛在每个农场的 AMS 软件上收集牛奶数据，并将其转换为 4 种不同的 F:P 值：（1）与 BHB 测试同一天的值；（2）5d 中心移动平均值（CMA）；（3）5d 后向移动平均值（BMA）；（4）5d 前向移动平均值（FMA）。在线性回归模型中，所有 4 个值都与 BHB 相关，但斜率估计值不同，R 值较低：同一天（斜率=0.95，R=0.07），CMA（斜率=1.05，R=0.07），BMA（斜率=0.65，R=0.04），和 FMA（斜率=1.23，R=0.09）。在逻辑回归模型中，每增加 0.1 个单位，F:P 比值（1.16）的均值（使用当天的值），HYK（BHB≥1.2mmol/L）的发生几率就会增加（比值比=1.35，95%置信区间=1.25-1.47）和 CMA（比值比=1.39，95%置信区间=1.27-1.51）。从均值 BMA（1.14）和 FMA（1.17）的 F:P 相同增加与 HYK 的几率分别增加了 1.22 和 1.49 倍。对于所有 4 种 F:P 变化，我们评估了不同 F:P 阈值与 HYK 状态相关的灵敏度、特异性、阳性预测值和阴性预测值。随着 F:P 阈值从 1.17 增加到 1.50，灵敏度降低（范围：77%至 9%），但特异性增加（范围：58%至 96%）。同一天和 CMA F:P 截止值在敏感性和特异性之间达到平衡，范围在 1.18 到 1.22 之间；然而，即使在这些值上，我们也发现了很高的假阳性和假阴性率（范围：31%-39%）。这些结果表明，来自不一致校准传感器的在线乳脂-蛋白数据不应单独用于检测 AMS 牛群中的 HYK。
