"We looked into this carefully and determined the beef stock at greatest risk were those that were raised in feed lots - not that common in New Zealand."
With the support of industry good organisation Beef+Lamb, MPI had carried out some surveillance of cattle in feed lots, mostly in the South Island, the epicentre of the M. bovis outbreak.
"The animals were tested at slaughter in order to take samples ... there were no positive results," the spokeswoman said.
"We also consider that many dairy beef animals were tested in the response as part of our tests on neighbouring farms to infected properties. Again, no positives were found."
Meanwhile, newly released MPI reports on M. bovis investigations since the first outbreak last July said "confluence of multiple rare events" could have allowed the bacterial disease into New Zealand, possibly as long ago as 2015.
One of the three released reports identifies seven potential pathways for the disease but finds all "improbable – yet one of them resulted in entry".
"This is a common feature of past disease incursions which have occurred despite strong border protection, in that the confluence of multiple rare events precipitates establishment of infection," said one report.
The risk pathways investigated were imported embyros, imported frozen bull semen, imported live cattle, imported feed, imported used farm equipment, and other imported live animals. A seventh pathway was redacted from the reports along with all discussion about it, but the Herald can confirm it was imported veterinary medicines and biological products.
MPI has opted to try to contain the disease with a mass cull of cattle on 28 quarantined properties, all but one in the South Island, because it believes it is not yet well established in New Zealand. The first outbreak of the disease was on a large-scale dairying business in the South Island. However, the MPI reports suggest it may have been introduced in mid-2016 or even earlier.
M. bovis is established in the herds of New Zealand's trading partners and other countries where authorities have chosen to try to manage it.
Given the economic importance of dairying and the beef industries, MPI wants to first try to get rid of M. bovis, with the cull to be completed before June 1, the start of the new dairy season when thousands of dairy herds are moved around the country to new milking jobs.
Mbovis is described by experts as a major, but often overlooked, pathogen causing respiratory disease, mastitis and arthritis in cattle. In recent years it has spread into new countries including Ireland and parts of South America. It is the smallest of all bacterias, and has no cell wall, which makes it challenging to treat with antibiotics. Experts say evidence is accumulating that strains of M.bovis are becoming resistant to antibiotics.
Mbovis is spread by contact between animals. It does not pose a food safety risk, according to MPI.
It said its investigations revealed major deficiencies in the practical operation of NAIT, the National Animal Identification and Tracing System.
The reports said there was also a need to resolve major shortcomings in information systems available to MPI for managing disease incursions and control activities.
