Bacteria are propelled into the teat canal and teat cistern when there is admission of undesired air into the milking unit. Also after milking the sphincter muscle in the teat canal remains dilated for 1-2 hours and bacteria present during this time can enter the teat canal. Liner slips, created by vacuum fluctuations, can propel bacteria through healthy teat ends. Trauma to the teat renders it more susceptible to bacterial invasion, colonization, and infection because of damage to keratin or mucous membranes lining the teat sinus. The canal of a damaged teat may remain partially open.
Invasion is easy because the offensive line has left a gap.
Try to minimize conditions that are associated with high impact force against the teat end, including liner slips, excessive temporary vacuum losses, low vacuum reserve or level, inefficient vacuum regulation, blocked air vents, restrictions in the short milk tube, poor cluster alignment, abrupt milking unit removal without shutting off vacuum, or poor liner condition. If the offensive line is doing its job, it becomes easier for somatic cells to clean up.