Effect of pulsation rest phase duration on teat end congestion

The objective of this study was to quantify the effect of d-phase (rest phase) duration of pulsation on the teat canal cross-sectional area during the period of peak milk flow from bovine teats. A secondary objective was to test if the effect of d-phase duration on teat canal cross-sectional area was influenced by milking system vacuum level, milking phase (b-phase) duration, and liner overpressure. During the d-phase of the pulsation cycle, liner compression facilitates venous flow and removal of fluids accumulated in teat-end tissues. It was hypothesized that a short-duration d-phase would result in congestion of teat-end tissue and a corresponding reduction in the cross-sectional area of the teat canal. A quarter milking device, designed and built at the Milking Research and Instruction Laboratory at the University of Wisconsin-Madison, was used to implement an experiment to test this hypothesis. Pulsator rate and ratios were adjusted to achieve 7 levels of d-phase duration: 50, 100, 150, 175, 200, 250, and 300 ms. These 7 d-phase durations were applied during one milking session and were repeated for 2 vacuum levels (40 and 50 kPa), 2 milking phase durations (575 and 775 ms), and 2 levels of liner overpressure (9.8 and 18 kPa). We observed a significant reduction in the estimated cross-sectional area of the teat canal with d-phase durations of 50 and 100 ms when compared with d-phase durations of 150, 175, 225, 250, and 300 ms. No significant difference was found in the estimated cross-sectional area of the teat canal for d-phase durations from 150 to 300 ms. No significant interaction was observed between the effect of d-phase and b-phase durations, vacuum level, or liner overpressure.