Mastitis is an inflammation of the udder caused by microorganisms that enter the gland through the teat canal. Once inside the gland, these organisms find ideal conditions in which to multiply and, in turn damage the lining of the milk ducts, cistern, and alveoli. Contagious bacteria are spread from a cow with an infected udder to a healthy cow.
Transfer of pathogenic bacteria between cows usually occurs at milking time. Milker hands, towels, or the milking machine can all act as reservoirs for contagious bacteria. The major contagious pathogens are Streptococcus agalactiae, Staphylococcus aureus, and Mycoplasma spp.
The most important approach to minimize the transmission is to address potential sources of contagion at milking time. Cleaning the cluster between milkings has been used in commercial farms for quite some time. However, submerging the cluster in hot water (85°C) has been found not very effective in reducing the number of new intramammary infections.
Similarly, flushing has not achieved the complete eradication of new infections. Flushing with just cold water is frequently used in commercial farms since it is less costly, does not damage the equipment that much, and reduces the risk of residues in milk. Adding disinfectants to the water has also been explored as an alternative solution.
Using an iodine solution has been demonstrated to reduce intramammary infections by Corynebacterium bovis and coagulase-positive staphylococci. Given these results it seems that teat cleanliness, teat dipping, and an adequate milking routine are more effective in reducing the spread of infections than the attempts at washing or disinfecting the unit.