Fact Sheet: Mycoplasma Mastitis

The Disease

Mastitis caused by an organism called mycoplasma is being diagnosed more commonly in New York State dairy herds. The most dangerous feature of this infection is it’s resistance to antibiotics. This highly contagious organism may be spread from infected cow to uninfected cow by milkers hands, milking equipment or aerosol spray of milk from infected cows. Also poor technique in the use of intramammary infusions can spread the infection. The disease may be brought onto a farm by a purchased cow or heifer or one returning from other housing. Also the disease can crop up as mastitis after originating as a respiratory problem, usually in calves. Mycoplasma is a common respiratory resident in cattle. The disease can only be diagnosed by using special culture techniques on bulk tank milk or milk from an individual cow. Once a cow is infected she may shed the organism for the rest of her life. Also a cow may shed many organisms in her milk before she appears sick, making control more difficult.

The Consequences

In the early stages of mycoplasma infection, before the cow shows signs of illness or abnormal milk she my shed the organism in her milk. This makes her a unrecognized threat. The first clinical sign of infection may be a sudden drop in milk production in any or all quarters, sometimes to near zero. This may be followed
by a thicker appearing milk that with time shifts color through yellow and tan and changes consistency to watery with clots and fibrin. The cow should appear recovered in two weeks but will continue to shed organisms and produce below expectations. As there is no truly effective treatment the increase in incidence of sever mastitis cases that don’t respond to treatment may indicate the presence of mycoplasma. The association of a respiratory disease problem on the farm with mastitis increases the suspicion of mycoplasma as the cause. The only way to determine if there is mycoplasma in a herd is culturing individual mastitis cases or repeated culturing of bulk tank milk using special techniques required to grow mycoplasma. With strict adherence to proper control procedures mycoplasma can be eliminated from a herd.


  • Culture all incoming replacements, cows and heifers, for mycoplasma as well as other more common contagious udder pathogens.
  • When buying a herd, culture bulk tank milk as well as all mastitic cows for mycoplasma.
  • Segregate young stock from milking animals as heifers are prone to mycoplasmal respiratory disease.


  • Suspect cows and bulk tank milk are cultured repeatedly for mycoplasma.


  • Culture bulk tank samples repeatedly.
  • Culture all newly lactating animals.
  • Culture all cows with clinical mastitis or long term high scc.
  • Cull or isolate all positive cows.
  • Infected cows are milked last or with separate equipment.
  • Strict sanitation when treating cows with intramammary infusions, disinfect and glove hands prior to treatment.