Mycoplasma bovis (M. bovis) is a bacterial disease that causes pneumonia, arthritis and conjunctivitis in calves, and mastitis and arthritis in adult cattle. Calves can contract the disease through direct contact with infected cattle, or consuming milk from cows that have M. bovis.

Testing herds for M. bovis is complex, which means negative results are a good sign – but not definitive proof that a herd is completely free of the disease. Furthermore, M. bovis can lay dormant for years and then show itself in times of stress.

That’s why it’s vital that we, as a sector, take every precaution possible to prevent it from spreading. This includes buying calves or milk, when it’s vital to take biosecurity practices and animal health history into account.

When buying calves

1. Purchase from as few sources as possible.
2. Deal directly with the source farm or via an agent.
   • Ask about any M. bovis test results available for the farm.
   • Ask about cow and calf health on the farm for the past two seasons, and use the pre-purchase checklist available at dairynz.co.nz/mbovis
3. Avoid buying from saleyards because of the cattle mixing that occurs there.
4. Purchase only calves with NAIT tags and promptly record all movements.
5. Insist your transporter avoids mixing calves with other cattle in holding yards or on the truck.
6. Keep purchased calves isolated from your main group for seven days and monitor them for signs of disease.
7. Find a buyer now for your future weaned calves, if possible, and tell the buyer about your efforts to reduce risk of M. bovis exposure.

When buying feeding milk

1. Milk that has the lowest risk of containing M. bovis bacteria comes in three forms: calf milk replacer powder, pasteurised milk, or acidified milk.
2. If you’re using milk replacer powder, order now to avoid problems with supply.
3. If you’re feeding whole milk, consider the following:
   • If the milk you’re feeding is discard milk from cows under treatment for illness, remember these cows are more likely to shed M. bovis into their milk than healthy cows.
   • M. bovis is not killed by the addition of potassium sorbate preservative (colostrum keeper) or yoghurt.
   • Pasteurisation will kill M. bovis if the machine is working well and the proper procedures are followed.
   • Acidification with citric acid or propionic acid to a pH below 4.3 will kill M. bovis but below a pH of 4 the milk will be unpalatable and calves will refuse to drink it. If you are interested in this option, it’s best to discuss acidification with your vet.

For more information see dairynz.co.nz/mbovis including:

• our Biosecurity WOF
• our Protecting your farm checklist
• the latest news on M. bovis

This article was originally published in Inside Dairy June 2018