So long as these coatings are undisturbed there may be little trouble but if the lines are disturbed for some reason, such as construction or whatever, they may be released in large quantities and can lead to problems. Species of Pseudomonas are also capable of causing a difficult to treat form of mastitis. Fortunately Pseudomonas mastitis occurs relatively infrequently. There is ample food and the temperatures are perfect. As a result there is a gradual increase in bacteria counts as milking times are extended.
Filters are a location that can cause problems.
Switching to new filters every 4-5 hours is recommended for systems with long milking times. L ong milking times cause the bacteria count to gradually rise as the milking proceeds. Occasionally on farms there is a need to divert milk from the latter part of the milking into a separate tank because the main tank is full. In this instance the overflow milk, placed in the alternate tank, would have the highest concentration of bacteria of all the milk harvested during that milking. It would consist only of milk that had passed over surfaces that would have been in use for many hours and likely experienced bacterial buildup.