M. bovis: Are your calves affected?

Having first arrived in the UK in the 1970s Mycoplasma bovis (M. bovis) is now considered endemic in UK herds. Blood samples from 156 farms taken in 2023 found evidence of infection in 65% of herds and a recent survey of 181 Scottish dairy herds found 86% were positive on bulk milk antibody testing. The ability of M. bovis to evade treatment and its highly contagious nature poses a challenge to both dairy and beef herds.

Clinical signs

M. bovis infections in cattle can present with a range of clinical signs. Affected animals may show signs of coughing, nasal discharge, fever, ear and joint infections or mastitis. Respiratory disease is the most common manifestation in calves and can range from mild symptoms to severe disease, with calves affected by M. bovis often developing a chronic cough and failing to thrive.

Key signs to look out for:

• Chronic, ‘poor doing’, coughing calves
• Drooped ears, a head tilt, head shaking, ear rubbing or discharge from the ear canal, which are all symptoms of ear infection
• Swollen joints and lameness, which can be symptoms of arthritis.

In adult cows, severe non-responsive clinical mastitis or sub-clinical mastitis.

Diagnosis

The clinical picture of respiratory disease diagnosed as M. bovis is often not characteristic and can be similar to the clinical signs caused by infections with other bovine respiratory tract pathogens. If faced with an outbreak of respiratory disease, diagnostic testing is a key step in identifying the underlying challenge and developing an effective control programme.

Testing specifically for M. bovis can either look for active infection or evidence of exposure. Active infection is confirmed by identifying bacteria in samples either by culture or using polymerase chain reaction (PCR). Screening for evidence of exposure is carried out by testing for antibodies in either milk or blood.

In dairy herds, bulk milk PCR testing and bulk milk serology can be useful methods for screening the herd for the disease. Alternatively, blood samples collected from a group of calves can provide useful information on whether or not there is M. bovis circulating in your youngstock.

Treatment

Mycoplasmas have no cell wall and are therefore naturally resistant to some commonly used antibiotics. It is therefore important to review your treatment protocols for respiratory disease with your vet to ensure you are using the correct products.

As for most diseases, early identification and intervention will increase the likelihood of treatment success. It is essential that everyone looking after calves on your farm can rapidly identify the signs of disease and implement the correct treatment. Supportive care is also an important component of treatment; your vet will be able to advise on how best to treat cases of M. bovis.

Control and prevention

The control of M. bovis in infected herds can be challenging – outbreaks are often part of a multifactorial infection picture, so it is essential to have a holistic approach to calf health to minimise the impact of this disease.

M. bovis can be transmitted directly from calf-to-calf through nose-to-nose contact or aerosols, or indirectly through contaminated feeding utensils and equipment. Calves may also become infected through the ingestion of contaminated milk or colostrum.

Control measures include:

• Ensuring optimum colostrum feeding
• Reducing transmission between groups by operating an all-in-all-out policy and disinfecting between batches
• Limiting routes of transmission from adult cows to calves by removing calves from the dam as soon as possible after calving
• Minimising shared airspace between groups and having good ventilation
• Not feeding waste milk or pooled colostrum and feeding only pasteurised colostrum
• Disinfection of feeding equipment.

Concurrent infections from other pneumonia pathogens like RSV and Pi3 viruses are often observed, and when combined with M. bovis, may increase the severity of disease. It is therefore important to consider routine vaccination against the common viral pneumonia agents to reduce the overall bovine respiratory disease risk.

If testing reveals M. bovis is not present on your farm, attention should be placed on prevention by maintaining a closed herd and robust biosecurity. 

Vaccination against M. bovis is also effective in reducing the severity of infections in calves. The UK now has one licensed vaccine for M. bovis: Protivity. It is the first modified-live M. bovis vaccine which can be used in calves from one week of age to reduce clinical signs and lung lesions caused by M. bovis infection.

In challenge studies, animals vaccinated with Protivity showed a 74% relative reduction in lung lesions, compared to control animals, and unvaccinated animals had significantly longer duration of fever and clinical signs versus vaccinated animals. In field studies, the use of Protivity in beef animals has been associated with an increase in average daily liveweight gain of 100g, and a significant reduction in antibiotic use.

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