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Mastitis Case Studies

Types of Mastitis/Modes of Transmission

This resource describes the modes of transmission of mastitis-causing bacteria, including Contagious Mastitis, Environmental Mastitis, Teat Skin to Udder, Mouth to Udder, and Flies

Contagious Mastitis

Contagious mastitis is sometimes referred to as Cow-to-Cow mastitis because it is generally spread from cow to cow. The primary habitat of bacteria causing contagious mastitis is on the udder and in teat lesions. These bacteria have poor survival in the environment when not associated with the skin or in the gland. Contagious mastitis is the type of mastitis in chronic or subclinical mastitis. The infection is transmitted by milk-contaminated fomites at milking, by a sponge used to wash the cow's teats, by the milker's hands, and by the milking machine. The major organisms causing contagious mastitis are Streptococcus agalactiae, Staphylococcus aureus, or Mycoplasma.

Machine stripping a cow with a milking machine.

Environmental Mastitis

Environmental Mastitis is sometimes referred to as Environment-to-Cow mastitis. In this case the bacteria that cause the mastitis are found in the cow's environment. The incidence of environmental mastitis tends to increase as the incidence of contagious mastitis decreases. The primary habitat of bacteria causing environmental mastitis is in the environment (feces, soil, bedding, or water). It can occur during environmental contact of the teats at milking time or between milkings. The major organisms causing environmental mastitis include the coliforms, the environmental Streptococcal species, and Pseudomonas species, but other organisms found in the cow's environment can cause mastitis, too.

Teat Skin to Udder

This is usually cause by Coagulase negative Staphylococci or Corynebacterium bovis. These are considered minor pathogens which cause streak canal infections. Their presence may provide protection against major pathogens, however this is still controversial. Germicidal teat dips and dry cow antibiotic treat are effective control measures.

Mouth to Udder

Calves suckling results in opening the teat canal, predisposing to IMI. Feeding calves with milk from cows that have mastitis may expose the calf (tonsils), although this is controversial; suckling may cause this type of mastitis, again this is controversial. The organisms associated with this mode of transmission are Strep. agalactiae and Staph. aureus, again these are controversial.


Sometimes can transmit what is called summer mastitis which is caused by Actinomyces pyogenes; this is gram positive and an environmental organism. It causes abscesses and purulent mastitis in dry cows and heifers. Also, Staph. aureus mastitis in heifers often occurs before calving and may be transmitted by flies.

Mastitis Case Studies
Mastitis Resources