# Evaluation of Two Practical Field Methods for Estimating Operational Overmilking Duration Using Standard Milking-System Sensors

## TL;DR

This study compares two methods for measuring overmilking in dairy cows and finds that they capture different aspects of the milking process.

## Contribution

The study identifies cow- and milking-level factors influencing method-to-method variation in operational overmilking duration estimates.

## Key findings

- Rear quarters showed the smallest method-to-method differences in overmilking duration estimates.
- VaDia™ estimates indicated longer overmilking durations compared to milk flow curve estimates.
- Factors like teat diameter, teat length, and parity influence method-to-method variation in overmilking measurements.

## Abstract

The objective of this study was to evaluate the method-to-method variation between the use of mouthpiece chamber (MPC) vacuum data from VaDia™ recorders and estimates based on simulated automatic cluster remover thresholds using milk flow data to quantify the end-of-milking vacuum-exposure period (i.e., operational overmilking duration) in dairy cows. Overmilking was defined using MPC vacuum fluctuations and milk flow curves at thresholds of 0.2 to 0.8 kg/min. Seven quarter combinations were analyzed, with rear quarters showing the smallest method-to-method differences. These findings demonstrate that vacuum-based and flow-based indicators of operational overmilking capture different aspects of the end-of-milking process and should be clearly specified when measuring or reporting overmilking in research or commercial milking evaluations.

The objective of this study was to quantify the method-to-method variation between two widely used field indicators of the end-of-milking vacuum-exposure period (i.e., operational overmilking duration), and to identify cow- and milking-level factors associated with this variation. Operational overmilking was defined using two approaches: (i) MPC vacuum fluctuation patterns collected via VaDia™ recording devices, and (ii) milk flow curves generated from milking system data, with simulated ACR take-off thresholds ranging from 0.2 to 0.8 kg/min. Seven quarter combinations were analyzed to determine their effect on method-to-method variation. Multivariable modelling was used to investigate the factors which influenced the absolute difference in operational overmilking duration (ADOD) between methods, with larger ADOD indicating greater method-to-method variation. All quarter combinations showed large method-to-method variations. VaDiaTM-derived estimates indicated longer overmilking durations and higher milk flow at the onset of overmilking compared with the milk flow curve approach. Our findings showed that a combination of the rear quarters was significantly associated with the lowest ADOD, and that a combination of the front quarters was significantly associated with the highest ADOD. All other combinations did not differ from each other, indicating that combinations including one front and one rear quarter performed similarly, and that recording all four quarters did not improve agreement between methods within this dataset. Milk flow factors associated with increased ADOD included longer low flow times, longer high flow times, longer machine-on times, and increased yield. Vacuum values associated with increased ADOD included high short milk tube vacuum during the full milking, and high mouthpiece chamber vacuum levels during both the full milking and overmilking periods. High short milk tube vacuum during overmilking was associated with decreased ADOD. Wider teat diameters, longer teat lengths, and increased parity were associated with increased ADOD. These findings indicated that vacuum-based and flow-based indicators of operational overmilking capture different aspects of the end-milking process and should be clearly specified when measuring or reporting overmilking in research or commercial milking systems.