Comparison of 2 types of milk flow meters for detecting bimodality in dairy cows
Matthias Wieland, Anja Sipka
Abstract
The primary objective of this observational study was to investigate whether incremental milk flow rates (in the 0–15 s, 15–30 s, 30–60 s, and 60–120 s intervals) from electronic on-farm milk flow meters can be used to detect bimodal milk flow curves in dairy cows compared with the use of a portable milk flow meter. Our second objective was to study the concordance between an electronic on-farm milk flow meter and a portable milk flow meter for assessing the 2-min milk yield and total milk yield. In this cross-sectional study, data from 92 milking observations from individual cows were analyzed. We collected data on incremental milk flow rates, the 2-min milk yield, and the total milk yield simultaneously with an on-farm milk flow meter and a portable milk flow meter. Bimodality detected by the on-farm milk flow meter was defined as lower milk flow rates during any of the 15–30 s, 30–60 s, and 60–120 s intervals compared with the previous intervals (0–15 s, 15–30 s, and 30–60 s). Bimodality according to the portable milk flow meter (BIM LC ) was observed through automatic detection. κ statistics indicated good agreement between bimodality detected by the on-farm milk flow meter and BIM LC [κ (95% confidence interval): 0.69 (0.49–0.90)]. Using BIM LC as the gold standard, diagnostic test statistics for bimodality detected by the on-farm milk flow meter indicated moderate performance for sensitivity [0.73 (0.54–0.86)] as well as high performance for positive predictive value [0.83 (0.63–0.93)], specificity [0.94 (0.85–0.98)], and negative predictive value [0.90 (0.81–0.95)]. Receiver operating characteristic curve analyses revealed that the 30–60 s milk flow rate was the variable that best predicted BIM LC, yielding an area under the curve of 0.89. Pearson correlation coefficients (r) revealed a very strong correlation between the 2 devices for both the 2-min milk yield [0.97 (0.96–0.98)] and total milk yield [r (95% confidence interval), 0.97 (0.96–0.98)]. Additionally, intraclass correlation coefficients (ICC) and concordance correlation coefficients (CCC) indicated excellent agreement between the 2 devices for the 2-min milk yield [ICC, 0.97 (0.96–0.98); CCC, 0.94 (0.92–0.96)] and total milk yield [ICC, 0.97 (0.96–0.98); CCC, 0.97 (0.95–0.98)]. Therefore, we concluded that electronic on-farm milk flow meters that measure incremental milk flow rates can be used to detect bimodality in dairy cows and that on-farm milk flow meters facilitate precise measurements of the 2-min milk yield and total milk yield.