Comparison of 2 types of milk flow meters for detecting bimodality in dairy cows

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.