Interruption of machine milking in dairy cows: effects on intramammary pressure and milking characteristics

Experiments were designed to test the hypothesis that milk ejection rate decreases during milking, thereby causing insufficient refill of the cistern and decreasing milk flow rate towards the end of milking. In a first series of experiments machine milking of the left front quarters of 11 cows was interrupted for 2 min after removal of 25, 50 or 75% of expected total milk yield, while milking was continued in the other three quarters. Milk flow was recorded during machine-on times. Intramammary pressure (IMP) was recorded during premilking teat stimulation and during interruption of milking. IMP during interruption of milking decreased with decreasing amounts of milk remaining in the udder. The IMP did not change during these interruptions when they occurred after 25 and 50% of expected total milk yield was removed. Thus, the ejection rate could keep up with the milk flow or removal rate. However, IMP increased during interruption of milking following removal of 75% of total yield, although significantly so only in cows with a high milk flow rate. Obviously, more milk was removed than was transported to the cisternal cavity. It is likely that a reduced ejection rate caused the decreased milk flow rate. In a second series of experiments the pulsation ratio of the milking machine was changed from the usual 70:30 to 50:50 with the aim of reducing the milk flow rate and thus adapting to the ejection rate at the end of milking. The changed pulsation ratio caused a reduced peak flow rate and a prolonged high milk flow period, whereas the main flow rate did not change significantly.