The Ministry for Primary Industries is going back and taking a fresh look at some farms formerly infected with the cattle disease Mycoplasma Bovis, to double check that all risk of infection has been found.
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M Bovis can cause lameness, mastitis and abortions in cows and was first detected in New Zealand by MPI in 2017, after a large number of cattle on a South Canterbury dairy herd began displaying symptoms.
Since then 262 farms have been confirmed as having M Bovis.
The latest figures from MPI show 11 farms are classed as being actively infected, while the rest have been cleared of their stock and declared safe to repopulate.
MPI Mycoplasma Bovis programme director Stuart Anderson said the ministry would over the coming weeks be looking at all the information concerning 132 of the previously infected properties.
It would be applying new tracing tools and a greater knowledge of the disease, he said.
"We do have that confidence that we're getting towards this tail end of the process of finding infection out there. We know a lot more now about the disease and our ability to trace and fill in gaps, particularly through the likes of NAIT (National Animal Identification and Tracing) records, is so much better now than it was at the early stages of the programme.
"So, we're going back through and applying all those new tools and knowledge of the disease, just to make sure that there aren't any risks that are still remaining from those previously infected properties and, if there are, that we can address them and close them off and be sure that we have identified infection out there," Anderson said.
The farms being considered are based on farm type, the original lab testing data, and how infectious they were, he said.
Anderson said the work would be largely a desk-based exercise and he expected very few farmers would need to be contacted for follow up. He said while he realised the work may cause some anxiety, it was an important and common part of any big disease eradication programme.
M Bovis cluster in Canterbury grows by one
On Friday, MPI confirmed a new farm had tested positive for Mycoplasma Bovis - it is linked to a cluster in Canterbury and brings the number of actively infected farms to 11.
Anderson said the latest infected farm was a grazing block connected to the existing Canterbury cluster through animal movements.
"There are connections between all the properties in this cluster. What gives us confidence about it is that we are able to identify those connections, so far there haven't been any new properties that have emerged outside of that cluster that we can't explain. So, those things all give us confidence that we are working this cluster through," Anderson said.