Source: National Farm Animal Care Council

Code of Practice for the care and handling of farm animals – Dairy Cattle, Section 3.6

Mastitis is an inflammation of the mammary gland caused by bacterial infection. Most bacteria enter the udder through the teat orifices.

Mastitis is a production, food quality, and safety issue. From an animal welfare perspective, it can be a local painful infection for the cow that can, depending on the type of infection and the resistance of the cow, also cause systemic illness resulting in fever, dehydration, depression and even death.

Mastitis is recognized as a clinical infection when flakes or clots are seen in a milk sample, the infected quarter is swollen and/or hot to the touch, the milk appears thin, discolored or watery and/or the cow has a rapid pulse and loss of appetite. More often however, mastitis is subclinical. This means that infection, tissue damage, milk damage, and production loss occurs without causing visible changes in the milk, the affected quarter or the cow. Somatic cell counts are used to monitor the prevalence of subclinical mastitis.

For the development of strategic prevention programs for particular herd mastitis, infections are classified as arising from either cow or environmental sources. Mastitis caused by infections whose sources are the cows themselves is called contagious mastitis. Contagious mastitis spreads from infected cow’s udders and teat skin to uninfected cows at milking time (46). Staphylococcus aureus and Streptococcus agalactiae are the most common bacterial causes of contagious mastitis (47). Environmental mastitis occurs when bacteria from manure contaminating the cow’s environment enters the teat ends. Cows are at risk of environmental infections at all times during the day and year; hence new infections are not just associated with milking practices (46).

Mastitis prevention programs are developed for a herd using knowledge of the mastitis infections the herd is most at risk of, the milk quality objectives, the facility design, current management practices, concurrent diseases, environmental conditions, and labor availability. Prevention of new infections and elimination of existing infections are the main objectives of a mastitis prevention program.

Goals are developed by a producer in conjunction with their herd veterinarian, often in a stepwise fashion, to develop an approach to improvements in animal health and milk quality.

Overall goals to strive for are:

  • maintenance of a bulk tank milk SCC below 200,000 cells per ml (62)
  • reduction in the occurrence of clinical mastitis to two or fewer clinical cases per 100 cows per month (<24% of cows affected per year) (50)
  • eradication of Streptococcus agalactiae from the herd
  • maintenance of a low culling rate due to mastitis.

Mastitis infections can be prevented by reducing exposure of the teat ends to bacteria. Appropriate practices should be implemented depending on the source of the bacteria identified in herd culture programs.


  1. consult with the herd veterinarian to develop a mastitis diagnostic, monitoring and control program.

To prevent contagious mastitis infections:

  1. dip each teat of all cows after every milking with an approved (DIN) teat dip
  2. ensure dip covers the area of the teat skin that had contact with the teat cup liner (51)
  3. ensure infected cows are milked last or separately from uninfected cows
  4. implement a monitoring system using individual cow somatic cell counting and strategic milk culturing as recommended.

To prevent environmental mastitis infections:

  1. clean and dry teats before milking
  2. implement a bedding routine to keep stall beds clean and dry
  3. use adequate amounts of bedding to keep cows clean, dry, and comfortable (46)
  4. add new, clean, dry bedding to stall backs frequently
  5. keep alleyways, crossovers and walkways free of manure and mud
  6. design stalls to give cows 12 hours of rest time (37)
  7. use a stocking density of at least one stall per cow
  8. have all cows calve in a clean, dry maternity pen
  9. protect the teat orifices of dry cows during the dry period
  10. feed a ration that prevents stress on the immune system of fresh cows
  11. record clinical cases of mastitis and treatment as they occur
  12. assess clinical records of mastitis cases to detect herd-specific risk factors for environmental mastitis (65).

To eliminate existing contagious and environmental infections (reducing prevalence):

  1. treat cows at the end of lactation with an approved intramammary dry cow preparation, as recommended by your herd veterinarian
  2. treat cows shown to have antibiotic susceptible infections during lactation, as recommended by your herd veterinarian
  3. cull cows with incurable cases of mastitis.