DairyNZ say farmers need to "do their homework," this year when it comes to using AI or bulls this mating season, due to cattle disease Mycoplasma bovis.

"Unfortunately there isn't a silver bullet – there are pros and cons associated with both AI and bulls," says DairyNZ response manager Hamish Hodgson.

Dairy farmers are using a range of tactics including due diligence, quarantine, and virgin bulls, to keep their cows and farms safe from the cattle disease this mating season.

Mycoplasma bovis, which is mainly spread through close physical contact with infected animals, makes using bulls which have been exposed to other stock an added risk.

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This has made some farmers think twice about continuing to use a combination of artificial insemination (AI) and bulls, and consider extending AI to remove bulls from the equation altogether, or reduce the number required.

DairyNZ says they have received a number of enquiries from farmers over recent weeks wanting more information to weigh-up the risks and benefits associated with each approach.

Hodgson says the best thing farmers can do to protect their herd and farm is "do their homework".

While a lot of farmers have been considering adapting their usual approach, most aren't making drastic changes, Hodgson says.

The majority appear to be sticking with a combination of AI and bulls, despite reports some farmers were shying away from using bulls this season.

"There's been some murmurs that farmers were going to avoid using bulls and just use artificial breeding, however after considering the risk and the cost to their businesses few have elected to proceed with a full AI system due to the likely lowering of overall fertility stats, perceived costs, and increased labour for accurate heat detection".

"Those using bulls should still do their due diligence, check where they've come from and if they've been in herds with a history of disease. This is extremely important, especially if they're older bulls that have done a few mating seasons on other farms" says Hodgson.

He understood there had also been a spike in demand for virgin bulls which have had minimal exposure to other animals, reducing the biosecurity risk of bringing bulls on farm.

Farmers have also been asking about M. bovis tests for bulls, Hodgson says.

"There is a PCR (polymerase chain reaction) test that is highly sensitive and will detect if M. bovis is present in a sample, but the complex nature of the disease can make this challenging.

"Because infected animals only shed the bacteria intermittently it is dependent on M. bovis being present where the sample is taken, and on the day the animal is tested. This means a result of 'not detected' doesn't necessarily mean it's disease-free. That's why we're recommending farmers gather as much information as possible about the source of any bulls and don't rely on PCR results," he says.

It's recommended farmers using bulls keep them separate from their main herd for at least seven days to allow time for the disease to present itself if they're infected, Hodgson says

Any farmers concerned about the health of bulls should contact their veterinarian before introducing them to their herd.

For more information on mitigating the risks of M. bovis this mating season, visit dairynz.co.nz/mbovis.