Contagious and Environmental Mastitis Pathogens:

What is the Difference and Why Does it Matter?

Mastitis is caused by many different types of bacteria which invade the udder by gaining access through the teat canal. Once inside the gland, these microorganisms multiply and produce harmful substances that result in inflammation, reduced milk production and altered milk quality. Microorganisms that most frequently cause mastitis can be divided into two broad categories: contagious pathogens and environmental pathogens.

Contagious mastitis pathogens

The mammary gland of infected cows is the main source of contagious pathogens in a dairy herd. Transmission of contagious pathogens to uninfected quarters and cows occurs primarily during the milking process. Milk from infected quarters can contaminate milking machines, hands of milkers, and towels, which act as reservoirs of infection.

The major contagious pathogens are Staphylococcus aureus and Streptococcus agalactiae. These bacteria can be controlled effectively by procedures that prevent spread of bacteria at milking time including good udder hygiene, proper milking procedures, and post milking teat disinfection. Use of dry cow therapy can help eliminate existing infections and prevent new infections during the early dry period.

Mycoplasmas are another important contagious mastitis pathogen. Mycoplasma mastitis may be introduced to the herd by purchased animals and can be spread during milking. There is no effective treatment for mycoplasma mastitis, but the disease can be controlled by identifying infected animals followed by segregating and/or culling the infected animals.

Environmental mastitis pathogens

The primary source of environmental mastitis pathogens is the habitat of the cow (soil, plant material, manure, bedding, and contaminated water). Exposure to environmental pathogens occurs primarily between milkings. The most frequently isolated environmental pathogens are several species of streptococci and gram-negative bacteria such as Escherichia coli and Klebsiella.

Environmental mastitis pathogens cannot be totally eliminated from the cow's surroundings, but it is possible to keep pathogen numbers low by maintaining a clean and dry environment. This is important because the greater the number of bacteria present in the cow's environment, the greater risk of mastitis. Therefore, control measures must rely on limiting the exposure of teats to the various types of environmental bacteria. Proper bedding management and keeping the udders clean and dry at all times helps control environmental mastitis. Dry cow therapy helps control new infections by environmental streptococci in the early dry period.

Take milk samples to determine the pathogens

Since the methods of prevention and control are different for contagious and environmental organisms, it is important to correctly identify the pathogens causing mastitis in a herd. This can be determined by culturing milk samples from individual cows. Once the pathogens are identified, specific control programs can be developed and implemented on a farm.

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Note: This article is also available in Spanish:

pdf file in both English and Spanish, side by side
online article in Espanol
online version in English

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