Mycoplasma bovine mastitis is a highly contagious disease that results in milk loss and culling of infected animals. Frequently, this type of mastitis goes unrecognized in dairy herds and is spread in part by the sale of infected cows to unsuspecting buyers. The disease was first reported in the US in 1961 in the state of Connecticut. Since this time, Mycoplasma can be found in most states. It seems that we only need to look for mycoplasmas to find them.
Mycoplasmas and Mastitis
Disease detection at the herd level is usually made by isolation of mycoplasmas from either bulk tank milk or samples from cows with clinical mastitis. According to a study done by Quality Milk Promotion Services at Cornell University, Mycoplasma bovis is the most frequent and pathogenic bovine mycoplasma in the United States. It is been associated with a variety of bovine diseases such as abortion and low fertility, arthritis, keratoconjunctivitis, mastitis, pneumonia, and synovitis. Diseases caused by mycoplasmas are resistant to antimicrobial therapy although they are susceptible in vitro to several antibiotics. Mastitis caused by Mycoplasma spp. may be subclinical, clinical, or chronic. The affected cow lacks systemic signs of disease and continues to eat and drink normally.
Mastitis causing mycoplasmas are commonly found in the mucous membranes of the respiratory and urogenital tracts of healthy cows. However, stresses such as calving, extreme temperature variations, transportation, disease, or external trauma allow the organisms to enter other body tissues or enter directly into the mammary gland resulting in clinical mastitis. Herds with and without mycoplasma mastitis may contain both young and mature asymptomatic carriers. The young are exposed to the various mycoplasmas during calving by direct contact with the urogenital tract, from nasal discharges of the dam, and in the colostrum they receive from shedding animals. Mycoplasma spp. may be shed in nasal discharges of calves and in vaginal discharges of heifers at the time of calving. Thus, it is extremely important to realize that even though a dairy is not currently experiencing mycoplasmal mastitis, the organisms are more than likely present within the herd and the possibility of a mastitis outbreak always exists.
Cows of all ages and at any stage of lactation are susceptible; however, cows in early lactation seem to suffer more severely because of the increased mammary gland edema that occurs. In lactating cows the characteristic signs of mycoplasma mastitis are:
- An increase in severe clinical mastitis cases that resist treatment, but with little other effect on the cow.
- The involvement of more than one mammary quarter, sometimes all four.
- A marked drop in the milk production of affected cows.
- Abnormal udder secretions that may vary from watery milk with a few clots to a colostrum-like material.
Cows which continue lactating produce less milk than expected for the current lactation, usually with normal appearance but with high somatic cell counts. They may shed mycoplasma organisms intermittently for variable period.
Diagnosis of mycoplasma infection in milk depends primarily upon microbiological culture of udder secretions. The method is reliable, but it is time-consuming, as 3 to 7 days of incubation may be necessary before plates receive a final reading. Best recovery rates are achieved when fresh milk samples are plated soon after collection and delivery to the laboratory. Samples may be kept refrigerated for 3 days or frozen for longer periods before culturing on mycoplasma medium. A herd suspected by a veterinarian of having mycoplasma mastitis, based on history and clinical signs, should be cultured in order to establish the nature of the infection. Mycoplasma infections are frequently complicated by common bacterial infections appearing concurrently.
Most transfer of mycoplasma infection within herds occurs at milking time by means of milking machines, teat cups, and hands. Many new herd infections occur from the introduction of replacements with infected udders. Treatment of mastitis provides a good opportunity for spread from cow to cow, and even from herd to herd if rigid sanitary precautions are not followed. However, an outbreak of mycoplasma mastitis may occur in previously clean herds without introduction of animals or history of previous intramammary treatment.
There is no treatment for mycoplasma mastitis. Control of the disease relies on identification of infected cows by culture of composite or quarter milk samples from all milking and dry cows in the herd. All cases of clinical mastitis should also be cultured as well as all animals at freshening, including heifers and infected colostrum should not be fed to calves. In large herds, culture of bulk tank milk samples collected after milking each production group may be used as a method to locate groups in which mycoplasma infected cows exist. Then, individual composite milk samples can be used to identify the infected cows in those production groups.
Weekly monitoring of bulk tank milk to detect the presence of mycoplasmas should be encouraged to monitor the success of control procedures. Arizona DHIA offers weekly bulk tank monitoring for this purpose. Slaughter of all infected cows is recommended when a few animals in the herd are infected. The use of rubber or plastic gloves and disinfection of gloved hands between cows is advised when milking or treating cows in a mycoplasma infected herd. Single treatment devices are recommended if treatment for any other type of mastitis is necessary in herds known or suspected to have mycoplasma mastitis.
Spread of Mycoplasma spp. can be greatly reduced by good milking procedures. Premilking teat disinfection before applying teat cups and postmilking teat dipping should be used. Quality Milk Promotion Services favors the use of iodine products (0.5 to 1%) during mycoplasma bovine mastitis outbreaks. The use of backflushing for disinfection of milking units between cows is emphasized.
Great care should be used when purchasing cows and heifers. Milk from all replacements should be cultured for Mycoplasma spp. as well as for Streptococcus agalactiae and Staphylococcus aureus before allowing replacements to commingle with the herd. When herds are purchased, it is a good policy to culture all suspected mastitic cows as well as the bulk tank. All actions should be based upon the understanding of the highly contagious nature, slow recovery rates, and the ineffectiveness of treatment of mycoplasma infections.
With informed dairy farmers and alert veterinarians, most herd infections can be prevented or diagnosed early.
I hope this helps!