Measurement of machine-induced changes in thickness of the bovine teat.

Machine milking induced repeatable, short-term changes in thickness of the teat apex. These changes were measured with a spring-loaded caliper instrument under milking conditions that imposed differing forces on the teat apex. The mean percentage changes in teat end thickness (relative to the premilking values for individual teats) varied from 10% decrease up to 20% or more increase depending on the particular milking system used. The overall decrease in teat end thickness associated with cannula milking, milking at very low vacuum levels or milking with positive pressure pulsation may result from: (i) decrease in the intramammary pressure; and/or (ii) small changes in tone of teat musculature; and/or (iii) changes in the distribution of interstitial fluids in the teat apex. The overall increase in teat thickness caused by conventional or PKME milking systems results mainly from oedema (the extravascular accumulation of fluid). It is likely that milking equipment can, and should, be designed to minimize circulatory impairment resulting in oedema of the teat.