Mycoplasma bovis

There are certain key facts that need to be considered when investigating, managing and treating Mycoplasma bovis infections and some of them are discussed below:

• Mycoplasma species differ from many bacteria in that they do not have a cell wall. This is not just of interest to scientists as it means that some of the commonly used antibiotics which act against bacterial cell walls (such as the penicillins) will not work. As with all bacterial diseases, deciding on an appropriate choice of antibiotic, targeting that treatment to the right animals early in the disease process and reviewing treatment outcomes is crucial for success. Veterinary advice here is crucial.

• The main disease presentations seen with Mycoplasma bovis infections are pneumonia, middle ear disease causing an ear droop or head tilt, mastitis and arthritis seen as non-foot lameness with joint swellings. Unfortunately, many of these problems can be chronic with a variable response to treatment. Mycoplasma bovis infection may also occur with no clinical signs at all. Clearly Mycoplasma bovis is not the only potential cause of any of these disease signs. A veterinary assessment of the disease situation on farm, plus taking appropriate samples for diagnostic testing will be required to consider the role Mycoplasma species are playing on farm.

• One of the main risk factors for having Mycoplasma bovis infections in a herd is a large herd size and purchasing cattle. Ideally keeping disease out by having a closed herd is the way to go. If you can’t, consider the potential risks from what you are buying with your vet and how you are going to mitigate the risk. Always consider that there is potential risk from bringing in carrier cows into a herd that is not infected, as well as a risk in bringing disease free non-immune cows into a herd with active infection.

• One of the main ways that infection spreads to calves is through feeding infected / contaminated cows milk and colostrum. Once established in a group of calves then it will spread mainly by aerosol transmission. Clearly we need to feed colostrum to calves and therefore in endemically infected herds pasteurisation of colostrum could be considered. Not feeding cows’ milk or waste milk to heifer or bull calves will also significantly reduce the risk of disease transmission. In addition to ensuring adequate draft free ventilation without chilling calves, keeping calf group size small and the age range within the calf group narrow helps reduce the risk of disease spread from older to younger calves. Getting as close as possible to an ‘all in all out system’ will really help.

• For calf pneumonia, Mycoplasma bovis usually acts in combination with other viruses and bacteria. Therefore taking steps to ensure optimal environmental and feeder hygiene, ensuring calves are well fed with sufficient good quality calf milk replacer and reducing the challenge and effect of other respirator pathogens through vaccination will help for Mycoplasma control.
  
  

Surveillance data shows that Mycoplasma bovis accounts for less than 1% of the diagnosed causes of mastitis with other more common mastitis bacteria such as E coli or Streptococcus uberis being far more important. That said, on an individual herd basis some herds can experience a significant outbreak of Mycoplasma bovis mastitis, sometimes in conjunction with an arthritis at the same time.

Mycoplasma are generally considered a ‘contagious’ type of bacteria, that 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 (like segregation or culling of carrier cows) cows can be required.

Colin Mason – SRUC Veterinary Services Dumfries Centre Manager