"They are only a small group of farmers but it only takes a handful and then they will not get on top of this," he said.
MPI's policy on compensation for farmers who have their herds culled as a result of M. bovis is that they should be no better or worse off as a result.
Walling said compensation can be slow "but if you do the paperwork properly, then it's not too much of a problem".
Dealing with M. bovis, and herd culling, will not be easy for farmers, he said.
"It's hard for everyone. It's not something, when you go farming, that you expect to go through," he said.
No country has yet successfully eradicated the disease.
ASB Bank economists said the revenue impact of the cull is not yet clear cut as the potential loss in dairy production could be partly or completely offset by higher dairy prices.
The cull will involve 152,000 animals over 1-2 years - or an extra 126,000 on top of the planned cull to date.
The Government will cover 68 per cent costs and the dairy and beef industry bodies the remainder.
The estimated costs of attempting to eradicate Mycoplasma Bovis are $886 million over 10 years, against an estimated cost of $1.2 billion to manage the disease over the long term and an estimated $1.3 billion in lost production from doing nothing.
At this point the Government believes that 37 farms have infected livestock and 192 farms in total will face stock culling - 142 in the first year.
But high-risk animal movements have been traced to 3000 farms and 858 are under surveillance.