By Jessica Ireland-Hughes,

SRUC Veterinary Services

Mycoplasma bovis is a class of very basic bacteria that lack a cell wall and this unique feature creates significant challenges for scientists developing treatments as some of the most commonly used antimicrobials, such as penicillin, target the cell wall.

Mycoplasmas are the smallest and simplest organisms capable of self-replication, and have the ability to alter their shape and size in different environments. M bovis is one of the many pathogens that causes bovine respiratory disease (BRD). In the UK, BRD is considered the most common form of disease associated with M bovis.

Infected cattle often respond poorly to treatment and are persistently re-infected. Calves are also considered reservoirs of M bovis, meaning that they maintain and multiply the bacteria, and will be a continuous source of disease in contact animals.

Spread of the disease through trading of cattle, particularly calves, can be a significant issue. Middle ear disease is also a symptom of infected calves, presenting as a head tilt or ear droop, often just in one ear. Vets report that this disease presentation is now seen more commonly.

M bovis causes mastitis in adult cattle that is difficult to treat. Infected cattle secrete it in their milk and this is thought to be an important route of spread when feeding whole milk and colostrum to calves.

Less common symptoms include lameness, eye disease, infertility and abortions. Not all animals exposed to the pathogen will show clinical symptoms, as some may become asymptomatic carriers. These animals show no symptoms of disease but are able to infect others.

We do not know the cost of M bovis to the dairy industry, but we know that some farms are significantly affected due to reduced growth, reduced milk production, cattle deaths and veterinary costs. On other farms, the disease may go undetected with no impact.

Farm management and structure are known to influence the risk of herd exposure to M bovis and the rate of spread within the herd. We are lacking an understanding of between- and within-herd spread of it and the risk factors that are associated with the presence and absence of disease.

Operating a closed herd is the most effective way to prevent disease entering the farm, however few herds exist that are truly closed as one bull or a few breeding cows may be purchased.

A recent study in Finland introduced M bovis into two herds via artificial insemination from an M bovis-positive bull, highlighting another route of spread. It can survive for up to eight months in the environment, therefore clothing, feeding equipment, sand bedding and the milking parlour are potential sources of transmission.

There are tests available to diagnose M bovis which can either detect the presence of the pathogen or the levels of antibodies implying the herd has been infected. Treatment options are limited as some antimicrobials are ineffective.

There are many management practices that help reduce the risk of bringing M bovis into your herd and limit spread within, including:

• Pasteurising cow’s milk and colostrum before feeding to calves.

• Regularly cleaning and disinfecting calf feeding equipment and milking parlour.

• Separating cows when they are calving.

• Operating a closed herd.

• Good ventilation of calf housing.

Most of the research on M bovis has been carried out in other countries, so the industry is lacking information on how this disease spreads and manifests in cattle in the UK.

The global prevalence of the disease varies between and within countries. A study in China estimated 53% of dairy herds were infected whereas there's none in Canada and just 3.8% in Japan.

Scotland’s Rural College (SRUC) is currently recruiting Scottish dairy farmers to participate in a national prevalence study which involves submitting four quarterly bulk tank milk samples and completing a short questionnaire on general herd management. By doing this, we hope to gain a better understanding of the nature and spread of this pathogen in Scotland and determine which farms are more or less at risk of disease.

Dairy farmers should by now have received a flyer in the post with details on how to get involved. If you would like to find out more, please email