The ultimate measure of the effect of machine milking on udder health is the influence on the rate of new infection. However, the frequency of new infections under field conditions is generally low and heavily influenced by other factors. Controlled experiments are often carried out as challenge experiments to accelerate the rate of new infections, which obviously is not practical or possible in commercial dairy herds, Consequently, the effect of machine milking on udder health has mainly been evaluated indirectly through observations of the effects on teat condition.
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