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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

Mastitis, an inflammation of the mammary gland, is almost always the result of bacterial infection.

Dairy Pipeline: February 1997

by Tom Bailey
Dairy Production Medicine
Virginia-Maryland Regional College of Vet Medicine
Virginia Tech

The origin of the major species of mastitis-causing bacteria is often considered as being either Contagious or Environmental. This distinction, contagious or environmental, is also very helpful in understanding mastitis control strategies. Contagious mastitis pathogens are often associated with problems in the milking parlor. Therefore, if bacteria causing mastitis are isolated to be of the contagious type, the primary focus or strategy should be aimed toward events occurring in the parlor. Environmental pathogens are as the name implies, bacteria that gains entry to the udder while cattle are away from the parlor or in their environment. This does not mean that environmental pathogens cannot be spread during milking procedure, it implies that our primary focus would be aimed toward evaluation of the area where cows spend time from the parlor. Milking equipment can act as a fomite, or an instrument to spread mastitis organisms from cow to cow, or it can damage or irritate the teat end and allow entry of organisms into the udder. Since the route of infection of the mammary gland is through the teat end, numbers of bacteria on the skin and teat openings are important. If no bacteria get through the teat opening, no new mastitis infections will occur. The most obvious source of contamination by the milking machine is the teatcup liners. It has been demonstrated that bacteria placed on the liners at the milking of one infected cow persisted on that same liner for 6 additional milkings. Milking equipment maintenance is of vital importance to decrease the incidence of new infections and decrease the spread of mastitis in the parlor. Most problems with milking equipment is due to inadequate maintenance, which leads to malfunction. The following are recommendations for maintaining a functional milking system:


  1. Wash outside of milk line, receiver jar and trap, claws, and hoses.


  1. Remove pulsators and clean
  2. Replace filters and/or clean vacuum controllers
  3. Wash trap inside and out (inspect float)
  4. Flush pulsator line and vacuum lines
Every 4 months:
  1. Evaluate the pulsators

Every 6 months:

  1. Replace all pulsator rubber parts
  2. Replace pulsator hoses, air tubes
  3. Replace receiver jar gasket
  4. Replace all milk hoses
  5. Replace rubber hoses and rubber hose nozzles used to wash udders
  6. Check belts and oiler on vacuum pump

Evaluate the entire milking system every 6 months

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