Effect of overmilking on udder health.

This study evaluated the effect on udder health of extending the milking period with or without vacuum fluctuation. Eighty cows were allotted into treatment groups consisting of 1) Control milked with normal milking equipment and the milker removed as soon as milk flow ceases; 2) milked for 12 min with normal equipment; 3) milked 12 min with induced vacuum fluctuations; and 4) normal milking time with induced fluctuations. Groups 2 and 3 had more newly infected quarters than groups 1 and 4. However, there was no difference in the number of cows becoming infected. The increase in new infections is due to more quarters of already infected cows becoming infected rather than more new cows becoming infected. Extending the machine-on time appeared to increase the rate of cross infection presumably by lengthening the time of highest risk. Cows in groups 2 and 3 required more therapy of clinical mastitis which was a reflection of the higher new infection rate rather than of a change in trauma to the udder. Increasing the unit-on time had no apparent effect on external teat end condition.