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Control of Environmental Mastitis

Two management practices, postmilking teat dipping and dry-cow treatment, have been effective in the control of mastitis caused by contagious bacteria. These practices, however, have not proven effective in the control of environmental mastitis. Other contrasts exist between environmental and contagious mastitis as shown in Table 1.

Table 1 Contrasting characteristics of environmental and contagious mastitis.

Characteristic Environmental Contagious
Major bacterial species Streptococcus non-ag Coliform Streptococcus agalactiae Staphylococcus aureus
Primary location of organisms Animal's environment Inside udder
Visual signs Often clinical Often subclinical
Duration of infection Short Long
Bulk tank somatic cell count Often low Often high

Somatic Cell Counts

Individual cows, at the time of an environmental mastitis infection, often have elevated somatic cell counts (SCC) similar to those exhibited by cows with contagious mastitis. However, herds with an increased rate of environmental mastitis, unlike those herds experiencing an increased rate of contagious mastitis, often do not have extremely elevated bulk tank SCC.

Two characteristics of environmental mastitis may be used to explain this observed difference:

  1. Clinical nature of environmental mastitis: Because milk from cows with environmental mastitis is usually visibly abnormal, it is likely to be excluded from the bulk tank. Also, the clinical nature of environmental infections increases the likelihood of antibiotic therapy, therefore, requiring exclusion of the milk from the tank. By contrast, the milk from cows infected with contagious bacteria is usually put in the bulk tank as it often appears normal to the naked eye.
  2. Duration of infection: Because environmental infections are of relatively short duration, the number of infected quarters (or prevalence) in a herd at any given time is usually low (e.g. <10%). Even with a similar rate of new infections, herds with contagious mastitis may have 40 to 60 percent of the quarters infected. This is because contagious infections are typically of longer duration. Furthermore, the relatively short duration of environmental infections is the reason that individual cow DHI-SCC may not be a good indicator of environmental mastitis problems within a herd.

Season, Age and Stage of Lactation

Research at The Ohio Agricultural Research and Development Center (OARDC) indicates that season of the year and parity affected the rate of new environmental mastitis infections. Summer, with hot and wet weather, was the season with the highest infection rate. Older cows (2+ lactations) were shown to be more prone to infection than heifers. Furthermore, cows were more likely to become infected shortly after drying-off and near freshening than at other times.

Control Strategies

While contagious bacteria live primarily in the udder and are usually spread during milking, the cow is exposed to environmental bacteria throughout the entire day. Therefore, specifics of environmental mastitis control may vary somewhat from farm-to-farm; however, a basic overall strategy should address the following areas:

  1. Dry Cow Management: Research has shown that the risk of new environmental mastitis infection is greatest immediately after drying-off and again near freshening. Dry cow medications, as currently marketed, are only partially effective in preventing new environmental infections; however, dry cow therapy is still recommended because it greatly reduces the number of new environmental streptococcal infections that occur at drying-off. Therefore, a key objective in the prevention of new environmental mastitis infections must be the maintenance of a clean, dry and well-ventilated environment for dry cows.
  2. Vitamin E/Selenium: Rations deficient in vitamin E and selenium increase the risk of environmental mastitis. Current OARDC recommendations include supplementation for large breeds as follows:
    • Dry cows: Feed 1000 IU vitamin E per head per day (when not on green pasture) and 3 mg selenium per head per day; also inject 50 mg selenium 21 days prior to parturition.
    • Lactating cows: Feed 400-600 IU vitamin E per head per day and 6 mg selenium per head per day.
  3. Cow Preparation: An overall goal of good cow preparation should be the application of a properly functioning milker-unit to a clean, surface-dry teat. Predipping is a relatively new technique that may be helpful in reducing the number of new environmental mastitis infections in certain circumstances. Predipping consists of the application and removal of a germacide to the teats before milking. A variety of products and techniques have been used. Dairymen are advised to discuss specifics of the procedure with their veterinarian, fieldman or county agent before implementing the practice. The first rule must be to "Avoid Residues in Milk."
  4. Milking Technique and Milking Machine Function: Proper machine function is described in Dairy Guide Leaflet 504. In addition, recent research indicates that liner slippage during milking is definitely associated with new intramammary infections.
  5. Teat Sphincter Closure: A simple technique that may be beneficial in the prevention of environmental mastitis is to encourage cows to remain standing for 1 to 2 hours after milking. This allows time for the teat sphincter to close and is best accomplished by providing cows with fresh feed following milking.
  6. Environment: The number of new mastitis infections is proportional to the number of bacteria to which the teat-end is exposed. Therefore, reduction of bacterial numbers at the teat-end is the goal. Clean, dry, and well-ventilated are key words that describe a proper environment. Proper design and maintenance of free stalls and freshening pens, cleaning of alleys, parlor holding-pens and barn lots, and fencing cows out of muddy areas are several means by which this goal may be accomplished.


Environmental mastitis is usually accompanied by clinical signs. Bacteriologic culturing of milk from cows with clinical mastitis cases or high SCC can be used to determine whether contagious or environmental bacteria are involved and also which areas of management might require adjustment.

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This page was last updated on November 16, 2002