Mycoplasmal mastitis is potentially a highly contagious disease that can cause severe economic problems in affected herds. Mycoplasma bovis has also been associated with abortion, infertility, arthritis, pinkeye, ear infections, pneumonia and abscesses. The organism is very small, lacks a cell wall and requires special testing in the laboratory that is usually more expensive and time consuming than other bacterial cultures. Cows diagnosed as positive for Mycoplasma should be considered positive for life.
Cows of all ages and at any stage of lactation as well as dry cows are susceptible. In lactating cows, the “classic” signs include:
- Severe mastitis that doesn’t respond to treatment
- More than one quarter is affected (sometimes all four)
- Marked drop in milk production
- Abnormal milk (varies from watery milk with a few clots to very thick) although some do not show abnormal color or pus.
- Cow often continues to eat and drink normally
- Chronic cow’s milk is tan colored with “sandy” or flaky sediment
- May see lameness/swollen joints due to arthritis. Occasional pneumonia.
- Some cows go dry due to the mastitis but those that continue their lactation have less milk, high cell counts, and can shed the Mycoplasma organism intermittently throughout her lifetime
It is important to remember regardless of what is described in textbooks, mastitis will have a unique presentation on each farm independent of the microorganism causing it. Therefore diagnosis cannot be based on clinical signs alone.
Most mycoplamal infections are considered contagious and are spread from cow to cow during the milking process. This spread can occur at milking due to faulty milking machines, teat cups, contaminated intramammary treatments and milker’s hands. Many herd infections come from the introduction of replacements with infected udders. Large numbers of Mycoplasma organisms may be shed in the milk before the onset of clinical mastitis so rapid spread within the herd is possible. The organism is normally present in the respiratory and urogenital tract of healthy cattle but stresses such as calving, extreme temperatures, transportation, comingling, or adaptation to a new parlor may allow the organism to enter the body then travel to the udder via the bloodstream. Mycoplasma organisms can survive in wet environments and are less sensitive to freezing and thawing than true bacteria. For these reasons, bedding, shady areas, and ponds can also be areas of concern as sources of infection. It is important to realize that even though a dairy is not experiencing mycoplasmal mastitis, the organism may be present so the possibility of an outbreak always exists.
Diagnosis is based on culturing the organism from the milk. Culture of bulk milk tank samples is valuable for screening and surveillance although cases can be missed due to dilution and also the “hit or miss” nature of shedding. If positive on the bulk tank then individual testing is necessary. All fresh cows and all clinical cases of mastitis should be tested as well.