Mycoplasma: An Emerging Problem in Dairy Herds

Mycoplasmas were first isolated in dairy cattle in the 1960’s. They probably were around for centuries prior to that, but were undetected due to stringent culture requirements. Today hardly anyone in the dairy industry hasn’t heard of or feared introduction of mycoplasma into a herd. As herds expand and animals are moved from area to area, there appears to be an increase in the incidence of mycoplasma infections in dairy herds. Mycoplasmas are the smallest free-living organisms. They have a widespread distribution and can be present in mammals, reptiles, plants, and humans. Under proper conditions (moderate temperatures and moisture) many strains can remain infective and outside the host, free in the environment for weeks to months. Disease may be clinical and severe although the disease signs associated with mycoplasma are more frequently subtle to subclinical. In young animals, disease is most frequently observed as pneumonia or joint/middle ear disease.

Treatment can be very prolonged and difficult. The vast majority of antibiotics are ineffective for therapy. Many animals once infected either develop chronic disease with micro abscesses or joint damage and most become carriers for life. Such carriers can be essentially normal for months or years but may actively shed the organism in the future when stressed. During these subclinical periods the organism can be difficult or impossible to isolate via routine culture techniques.

Mastitis due to mycoplasma can be very difficult to prevent, control, or eradicate. Mycoplasmas are frequent residents of the respiratory tract of normal animals. When stressed these organisms spread in many secretions or via the blood stream. Bedding and the environment can be contaminated. The udder can become potentially be contaminated from the bloodstream, contaminated bedding, milking equipment or from caretakers hands.

This scenario is often played out during herd expansions. Producers purchase apparently normal healthy heifers. When these heifers are added to the larger herd, especially if air quality or nutrition place excessive stress on the heifer, it is not unusual for subclinical animals to begin to shed organisms into the environment or develop clinical signs. Cows of all stages of lactation are susceptible to infection. Cows during the transition phase or at peak lactation have the greatest susceptibility.

Classic signs of mycoplasma mastitis are: failure of response to treatment, multiple quarter infections, and udder edema often without fever, variable milk yield depressions and udder secretions that can range from watery to very thick and clotted. The organism is a contagious mastitis pathogen and once one animal is shedding the organism in her milk, it is easy to spread from cow to cow. Well trained milkers can be very helpful in identifying early infections. It is important that milker crews be trained to consistently follow established protocols for contagious pathogens. (e.g., clean latex gloves, individual towels, careful and complete post milk dipping with an effective germicide, and segregate-milk last known infected animals).

Most antibiotics approved for use in dairy animals are β lactams (penicillin like) and therefore are ineffective against mycoplasma. Much cost and lost time is consumed when producers attempt to treat mastitis due to mycoplasma. Known infected animals should be segregated immediately and as economic conditions dictate perhaps designated for early culling. Vaccines for mycoplasma are commercially available. Mycoplasma bovis is the most prevalent species isolated in diagnostic laboratories (>50%). However, there are approximately eleven other species of mycoplasma that have been isolated in cattle. It is important that the vaccine strain be similar to the strain isolated on the farm. This type of testing must be accomplished at a veterinary diagnostic laboratory. Immunization appears to be most effective if properly administered to heifers prior to their first infection.

Mycoplasmas are difficult to culture. A positive culture is very meaningful, a negative culture in a suspicious animal, indicates the need to repeat the cultures. PCR technology is available to detect mycoplasma. This technique is very sensitive and specific and shows great promise as both a screening tool for bulk tanks and in some individual cow cases.

For additional information on mycoplasma in herds or assistance in diagnostics please contact any of these members of the Department of Veterinary Science at PSU:

Dr. Brenda Love-Animal Diagnostic Laboratory 814-863-0838
Drs. Bhushan Jayarao, Ernest Hovingh, David Wolfgang 814-863-2160

Good review article and used in the development of this short discussion:

Gonzalez, RN and DJ Wilson, Mycoplasma mastitis in dairy herds, Vet Clin Food Animal 19 (2003) pgs. 199-221

David R. Wolfgang, Extension Veterinarian & Field Investigations