Calf rearing: Steps to reduce M. bovis risk

Calf rearing can increase the spread of infectious diseases including Mycoplasma bovis. Calves can become infected through direct contact with infected cattle, or by consuming their milk. Here are some simple steps you can take to reduce the risk of spreading disease.

Stock movements pose the highest risk

Any situation where animals from different farms and groups mix, presents a risk for spreading disease, including M. bovis.

If you can't avoid buying calves

  • Purchase from as few sources as possible.
  • When purchasing and mixing stock, consider the risk of spreading disease by mixing animals from different farms and isolated husbandry groups.
  • Ensure calves get adequate colostrum from healthy cows on their home farm. This is important for the development of the calf's immune system, making them better able to fight disease.
  • Deal directly with a trusted source farm or agent. Ask them:
    • about any M. bovis test results for the farm
    • if the farm has been subject to any M. bovis tracing by MPI, and the outcome
    • about stock management and trading practices on the farm
    • about the farm's biosecurity (such as double fencing or quarantine)
    • if all stock movement records are up to date and recorded in NAIT
    • about cow and calf health on the farm for the past 2 seasons – use the pre-purchase checklist on the DairyNZ website
  • Only purchase cattle with NAIT tags and promptly record all movements.
  • Ask your transporter if they can transport your cattle without mixing with others in holding yards or on the truck.
  • Keep purchased calves isolated from your main group for at least 7 days and monitor them for signs of disease.
  • Find a buyer now for your future weaned calves, if possible, and tell buyers about your efforts to reduce risk of M. bovis exposure.

Milk use for calves

Feeding infected milk to calves is a high risk activity in the spread of M. bovis. To limit the risk, avoid trading colostrum and milk.

If you are trading milk or colostrum for calves

  • Reduce the risk of M. bovis transmission from fresh milk by one of the following:
    • using calf milk replacer (CMR)
    • pasteurising the milk
    • acidifying the milk.
  • Good quality colostrum fed to calves in the first 24 hours of life promotes good calf immunity to infectious diseases.
  • Both pasteurisation and acidification destroy some antibodies in colostrum. This is only significant for colostrum fed to calves less than 24-hours-old as calves only absorb antibodies from colostrum for the first day of life.
  • Colostrum and milk that has been pasteurised or acidified is suitable for feeding to calves.
  • Milk from cows being treated for mastitis or other illnesses should not be fed to calves.
  • The lowest risk for spread of M. bovis is calf milk replacer. Good quality calf milk replacer has similar performance to raw milk.

Milk treatment advice


Pasteurisation will destroy M. bovis bacteria, if done correctly.

  • The recommended treatment is 60°C for 60 minutes.
  • Refer to manufacturer's specifications for operating the pasteuriser.

Acidification with citric acid

To kill M. bovis by acidifying milk, it needs to be at a pH of 4.5 for a minimum of 8 hours.

  • Citric acid is available online and will be available at other suppliers, including farm merchant stores, this spring.
  • Use cool milk (10°C to 24°C) or cold (less than 10°C) to minimise coagulation or clot formation.
  • Always add acid to milk, not milk to acid.
  • Acidification works best when citric acid is added to fresh milk.
  • It's important to accurately measure the weight of citric acid and volume of milk. Use a rate of:
    • 5.5g citric acid per litre of whole milk
    • 550g per 100 litres of whole milk
    • 5.5kg per 1000 litres of whole milk
  • Sprinkle the acid on top of the milk while the milk is being agitated.
  • Milk at pH 4.5 separates, but with gentle mixing goes back into a homogenous solution.
  • Do not acidify below pH 4 – this will result in:
    • thickened milk
    • risk of complete coagulation
    • calves not drinking the milk.
  • Gentle mixing of the milk twice a week is the recommended method. Continuous mixing causes coagulation, as does vigorous mixing.
  • For systems that pipe milk, the milk may coagulate in pipes or tubes with blockage of lines and nipples. This may result in the feeding of whey to calves if the casein coagulates.
Testing pH
  • Test the pH of milk half an hour after the addition of citric acid to the milk.
  • Test again just prior to it being fed to calves.
  • Use pH test strips. You can buy these online and in stores, including farm merchant stores.
  • It can be difficult to keep electronic pH meters clean and calibrated when working with milk – if using one, make sure you clean and calibrate it regularly.

Other treatment options

Acidification with yoghurt

Adding yoghurt to milk is a less reliable way to reduce milk pH.

  • The process takes longer and is temperature dependent to get the culture growing.
  • If the pH doesn't drop below 5 for at least 8 hours, M. bovis will not be killed.
Potassium sorbate preservative

M. bovis is not killed by the addition of potassium sorbate preservative.

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