Here are the reasons you seriously need to start caring about Mycoplasma bovis

Our cows are suffering, our farmers are suffering, and whether or not we can eradicate the disease, it's going to cost us many, many millions.

Here's why you need to care about Mycoplasma bovis.

It's a horrific disease for the animals

At its core, Mycoplasma bovis is an animal welfare issue. The bacterial infection doesn't affect the meat or milk produced by animals but it makes their lives painful and miserable.

In cows, it causes severe arthritis, late-term still births and untreatable mastitis. Any woman who has had this infection will know how painful it is. It's inflammation of the breast tissue, and is accompanied by tiredness and chills.

Calves have little defence against the disease. Farmers have described shooting their own calves on the spot because they were suffering so much.

It can cause a hacking cough leading to severe pneumonia, as well as ear infections and conjunctivitis.

"MPI did a cull on the property or we shot [them] just because of animal welfare reasons. They were just so poorly they couldn't carry on as they were," Southland farmer Ben Walling told RNZ. He had unwittingly bought the calves from an infected farm.

It's tough on farmers

Many of the cows being culled won't appear to be in poor condition because it's not until their body becomes stressed that the disease can take hold. For those ordered to cull their herd, that will make it even harder.

It's not just the act of culling. Farmers work hard at building up the ideal herd. Some herds have been worked at by generations - both the land and the cows are passed on from parent to child.

"The emotional part is when a person's lost their lifetime of breeding those cows," Forward Farming's managing director David Law told The AM Show this morning.

Federated Farmers dairy industry chair Chris Lewis had a similar message for Newshub.

"The human toll, the mental toll, the stress toll is massive."

"[Farmers] take the calves from the first day they are born and feed them and turn them into a beautiful calf. 

"You get quite close to your animals. [The cow is] with her parents, grandparents, great grandparents, which you've bred for the past 20 or 30 years."

Tens of thousands of cattle will be culled

All cattle on properties infected with the disease will be culled.

That's at least 22,000 cattle.

While 38 farms are currently infected, that could rise to 70 after cattle are shifted for the winter, Minister of Agriculture Damien O'Connor says.

That will mean the number culled could also rise, if MPI and the Government still think eradication is the best option.

It could cost a lot of money 

Not only is the disease horrible for animals to suffer through, it of course affects their productivity. Decreased milk production, late-term abortion and struggling calves cause an obvious slow down on the farm.

"The cost of culling and the cost of productivity have to be weighed up", the Prime Minister says.

In other words, the cost of killing thousands of cows in the hope of wiping out the disease has to be weighed up against the future cost of lost productivity if we accept the disease will stay. 

Even if it stays, the Government will likely still need to pay on-going costs controlling the spread. 

In the meantime, the Government is paying millions to supply feed to farmers who are not allowed to move their herds to greener pastures.

The Budget allocated $85 million toward fighting M bovis. That could rise.

Because New Zealand lacks a land border, we've been sheltered from the disease.

It's found all over the world, including in Australia, so if it does take hold here, it's unlikely to immediately affect trade. But it costs those infected countries in lost production and controlling the existing outbreak.

The cost of milk and butter could rise

If the outbreak of Mycoplasma bovis continues to cost farmers thousands, and if it creates a dent in milk production, it follows that the price of dairy products will rise.

It can be difficult to detect

"One of the issues we have is that unlike some other animal health issues, you can't necessarily establish in one simple test that an animal has bovis," the Prime Minister said this morning.

"You could be moving an animal that seems perfectly healthy and then discover at some point down the track when they are under some stress and strain, like a winter period, that they actually have the disease."

Thousands of animals are about to shift around the country

Every year as winter approaches, there's a huge migration. When grass stops growing in areas of the South Island, for example, cattle are shifted to where they can feed over winter.

That will happen June 1 - in about a week.

Farmers are being asked to check they are not moving infected animals but so far there's no plan to stop the movement.

But, as we outlined above, farmers could be moving cattle that look fine but are harbouring the disease.