Mycoplasma bovis can result in several different syndromes in dairy cattle as well as in beef cattle. Mycoplasma can cause mastitis, pneumonia, polyarthritis (multiple joint infections), and middle ear infections. It also has the ability to cause keratoconjunctivitis (inflammation of the cornea and conjunctiva), infertility, endometritis (inflammation of the lining of the uterus), and abortions.

Unfortunately, control is difficult because it can evade the immune system and has developed resistance to a number of antibiotics. This limits our options of controlling Mycoplasma infections and (without severe culling) the chances of eliminating it are few.

Mastitis caused by M. bovis can be seen in several forms. One is acute mastitis associated with herd expansion, but this is infrequent. Recurrent mastitis can be seen in herds that have recovered from the acute mycoplasmal mastitis. Herds with this tend to undergo three or more episodes a year. The cows usually have an abnormal quantity of flecks in the milk. Often, these are freshening cows. Infection may not be detected from bulk tank sampling. However, these herds often have increasing somatic cell count (commonly referred to as SCC) and many cows with environmental mastitis.

Heifers with mycoplasmal mastitis usually come from commercial sources. They present with mastitis at freshening that is resistant to treatment and can be a source of infection for the herd.

Cows or heifers that are suspected need to be cultured and kept separate from the herd to decrease transmission. Positive cows need to be culled.

In dairy calves, pneumonia and polyarthritis are usually seen on dairies that are feeding discard milk that is contaminated. Calves fed contaminated milk will present with pneumonia within two weeks of birth, and may also have swollen joints starting at three weeks of age. Larger dairies have gone to pasteurizing the milk to eliminate the Mycoplasma in the milk. Middle ear infections are seen in dairy animals of all ages but particularly in bucket-fed or bottle-fed calves..

Clinical signs in calves will appear around two weeks of age. Appetite and attitude are usually normal except during end stages of the disease. The first sign is slight tearing of the eye. In several days, one or both ears start to droop at rest and eventually stay in the drooped position. The calf may also have a slight cough and nasal discharge. If left untreated, the condition will persist for several weeks and can progress to chronic pneumonia and/or arthritis.

Incidence is high in calves fed non-pasteurized waste milk or contaminated colostrum. It can also be spread from calf to calf. High moisture in the environment will increase incidence and severity. It is seen more frequently in late winter and early spring due to more frequent precipitation when barns are not open enough to allow sufficient air exchange.

Treatment of individual cases can be successful if detection is made early. Micotil and long acting oxytetracyclines have been the drugs of choice for some practitioners. Draxxin, a new drug for pneumonia, has also been shown to have a positive effect on treating Mycoplasma and has become my drug of choice. Success also depends on the duration of treatment; it is recommended to keep the infected animal on antibiotics for seven to ten days.