The effect of milking machine liner slip on new intramammary infections.

New IMI of cows milked with high and low slip rate milking machine liners were compared. High slip liners used in this study averaged 6.1 initial slips and 7.6 major vacuum fluctuations per cow milking, and low slip liners averaged 3.6 initial slips and 3.1 major vacuum fluctuations per cow milking. Least squares means for new IMI rates per 100 cow days were .49 in the high slip group and .27 in the low slip group. Rates of clinical cases per 100 cow days were .35 in the high slip group and .20 in the low slip group. New IMI rates for cows entering the trial with an existing infection were .81 in the high slip group and .39 in the low slip group. More new IMI tended to occur with cows milked with the high slip liners than with low slip liners.