Dynamics of teat-end vacuum during machine milking: types, causes and impacts on teat condition and udder health – a literature review

Figures & data

Figure 1. Overview on the different types of vacuum changes which can occur during machine milking. A general drop of the vacuum level during the milking process occurs as soon as the milk flow rate increases. It depends of the milk flow rate, and of characteristics of the milking system (capacity; line height). An accumulation of milk in the claw and milk tubes, which needs to be transported through the system by the milk line vacuum, affects the free airflow and leads to the decrease of the vacuum beneath the teat. Changes have been defined as either vacuum drops or vacuum fluctuations.

Figure 2. Cyclic vacuum fluctuations of teat-end vacuum during milk flow. The figure shows the course of the vacuum level at the teat end of a milking system with alternating pulsation (left-right alternating). Only one of the two pulsation curves is shown whereas both pulsation curves cause similar vacuum fluctuations at all four teats, i.e., cyclic teat-end vacuum fluctuations occur twice per pulsation cycle. The liner opening and closure in the absence of milk flow causes only minimal vacuum fluctuations, i.e., the main cause of the fluctuations is the dynamic movement of the milk within the short milk tubes and claw. The liner opening causes a short increase of vacuum due to the enlargement of the volume inside the liner, followed by a decline of vacuum when milk flow starts. In systems with simultaneous pulsation, a cyclic vacuum fluctuation occurs only once per pulsation cycle, but fluctuations have a higher amplitude at a given milk flow level.

Figure 3. Pulsation curve and liner opening and closing without milk flow and during a milk flow dependent vacuum drop. Vacuum in the pulsation chamber causes liner opening, whereas the liner closure and pressure of the liner on the teat is determined by the teat-end vacuum (at atmospheric pressure in pulsation chamber). Therefore, the opening and closure of the liner occurs at a lower level of PCV. The additional vacuum for full closure of the liner, additional massage effect and the vacuum reserve defined as overpressure is reduced during vacuum drops and can theoretically be insufficient. The vacuum difference at start of stop of milk flow is usually close to the TPPD; it depends on not only the liner movement but also the characteristics of the teat.