Farmers, vets and scientists have been working with Mycoplasma bovis infections for many years. Despite this, we are still learning about exactly how and when it causes disease, and how best to prevent and treat it. Tim Geraghty, veterinary investigation officer at SAC Consulting explains more.
Mycoplasma are small bacteria. There are more than 125 different types and several which are found on cattle. They are different to most other bacteria because they do not have a cell wall around them. Mycoplasma bovis is the most common type which can be associated with disease in cattle in the UK.
Mycoplasma can be present in cows without causing any disease at all. When they do cause disease, it can be because the animal’s immune system is not working well, its environment is poor or because the type of mycoplasma is particularly aggressive.
In cattle, the major diseases mycoplasma can contribute to are pneumonia and mastitis and occasionally other problems including ear, eye and joint infections.
There are many other bacteria and viruses which also contribute to all of these problems and it is difficult to diagnose when exactly mycoplasma are involved. When they are involved they can also be difficult to treat.
The first problem is the diseases which mycoplasma typically contribute to are not only caused by mycoplasma. This means a farmer or vet cannot just examine a sick animal and tell whether mycoplasma are involved. A laboratory test is needed.
Mycoplasma are difficult to grow in the laboratory. Most bacteria will grow in about 24 hours but mycoplasma can take up to a week. They can also be masked by other bacteria which grow more quickly.These challenges mean they are difficult to study and learn about in the laboratory too.
Modern methods, like polymerase chain reaction (PCR) tests, can help as they do not need to wait for bacteria to grow. However, as mycoplasma do not always cause disease, when you find them you cannot always be sure they are causing a problem.
With regard to treatment, lots of antibiotics work by attacking the cell wall around bacteria. However, as mycoplasma do not have a cell wall, these type of antibiotics do not work. Even when an effective antibiotic is used, animals can still respond poorly. This may be because there is too much tissue damage already done or there is another infection with other bugs, such as like viruses. In some instances, mycoplasma can evade even effective antibiotics.
Mycoplasma do not live for long away from carrier animals so most spread between herds occurs by moving stock. In simple terms, the more animals you bring into your herd, the more likely you are to bring mycoplasma in with them.
Try to minimise stock buying and movement to only those which are absolutely essential. If you do need to buy-in animals, ask your vet to help with planning to reduce risk. There is no legal requirement, but blood tests are available which can help to identify potential carrier animals. For testing to reduce the risk, you need to be able to turn away animals which test positive, so planning where and when they are tested is essential.
Other basic biosecurity measures, like maintaining fencing which prevents nose-to-nose contact at farm boundaries, will also help to reduce risk.
Most dairy farms probably do not need a specific mycoplasma control plan. Instead, focus on reducing the major disease problems wihch mycoplasma can contribute to; pneumonia and mastitis. For both of these diseases, the environment and management of the farm can have as much influence as the specific bacteria, viruses or mycoplasma which contribute to them.
All farms are different, so regular discussions and reviews with your own herd-health vet are essential. Your vet can advise on both environment and management, and any appropriate diagnostic testing needed for monitoring. There are no commercial cattle vaccines for mycoplasma in the UK, so husbandry is even more important in prevention.
For pneumonia, focus on improving air quality and reducing stress from mixing, handling and uncomfortable accommodation. Include youngstock diets when planning nutrition to make sure they have the nutrients to grow and maintain immune function. Working on these will help control all causes of pneumonia, not just mycoplasma.
For mastitis, mycoplasma are generally considered a ‘contagious’ type of bacteria which will spread from cow to cow in the parlour.
Creating a milking routine to minimise cow-to-cow spread is the aim and again this will control much more than just mycoplasma. In some cases, if mycoplasma become established as a major cause of mastitis, more specific controls, such as segregation or culling of carrier cows, can be required.
The milk from affected cows should not be fed to calves as this may allow spread of infection