Another case of the cattle disease has been found - taking the total up to 25 infected farms.
First found in South Canterbury in July last year the disease is now spread from Southland to Hawke's Bay.
The Ministry for Primary Industries confirmed the latest case through a "stakeholder update".
It said 28 properties were infected, but of this number there were four farm blocks owned by the same farmer that had been grouped into a single site of infection.
The ministry said because of that change the total number of infected properties was officially 25.
However, it said because cattle from two farms had been removed and legal restrictions lifted, the number of 'active' infected properties was actually 23.
A new study from Norway suggests mycoplasma bovis can be transmitted through frozen straws of semen.
The researchers said that to their knowledge it was the first study which described how mycoplasma bovis could be introduced to a herd through processed semen.
The study found the disease was introduced into two dairy herds through contaminated semen used for artificial insemination.
In New Zealand there's been speculation that the disease might have got in via imported semen, but to date there's been no answer as to how the disease made its way here.
Livestock Improvement (LIC) provides 80 percent of New Zealand's cattle breeding semen, and chief executive Wayne McNee says the new research from Norway is significant.
"This is the first time that I've seen a study which suggests that m.bovis could be carried in semen, so I'm sure it's something that MPI will be looking very closely at."
Mr McNee said LIC took its biosecurity very seriously and was confident that none of their bulls were infected with mycoplasma bovis.
"We've been testing all of the bulls that we have, testing every bull that we bring in ... all the young bulls are brought in and put in quarantine.
"We're also making sure that our staff, when they visit farms, are using wash stations and carrying disinfectant with them."
The new study from Norway would not change anything at LIC, he said.
"We've already put all the precautions in place that we possibly could to ensure that the bulls we collect from don't have m. bovis.
"But I'm sure this study is something that MPI and others will be looking at very closely."