Mastitis infection from abrupt loss of milking vacuum

During a single reversal trial of two 2-wk experimental periods, teats of all glands of 12 Holstein cows were subjected to a milking routine conducive to large vacuum fluctuations and flooded teat cups. High pathogen contamination was produced by continuous infusion into the long milk tube of 10(10) colony-forming units of Streptococcus agalactiae per min. At each milking, teat cups of control glands (two per cow) were clamped at the short milk tube and removed after milk ceased flowing. As inflations were opening, we subjected teats of the remaining (treated) pair of glands to abrupt vacuum drop by venting the long milk tube at its connection to the bucket of the milking machine. Excluding glands infected at starts of periods, 10 (22%) of 45 treated glands versus 2 (5%) of 43 control glands became infected with Streptococcus agalactiae (criterion: Wisconsin mastitis test rise plus positive culture at two consecutive milkings). We concluded that the rapid airflow toward teats which resulted from sudden vacuum loss characterizes vacuum abnormalities associated with increased risk of mastitis infection.