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The first test results from seven of Van Leeuwen Dairy Group's farms have returned negative for cattle disease Mycoplasma bovis.
The bacterial disease has previously been confirmed on two VLDG properties in the Waimate district, the first time the disease had been detected in New Zealand.
In an update yesterday, response incident controller Eve Pleydell said two further rounds of testing would be required on those seven farms before they could be declared free of the disease. Results were pending for the remaining seven VLDG properties.
Good progress was made during the weekend, as laboratory teams continued to test thousands of milk and blood samples from VLG farms and neighbouring properties, Dr Pleydell said.
To date, 2610 samples had been received. Nine of the 62 neighbouring properties had so far tested negative.
Dr Pleydell said it was important to find out if the disease was already occurring in other parts of the country.
The Ministry for Primary Industries was working with regional veterinary laboratories, Massey University and animal industry bodies to collect and analyse samples, including milk from cows with mastitis, discard milk and routine bulk milk samples.
The first samples from the regional laboratories would be arriving at MPI's animal health laboratory, at Wallaceville, this week.
One of the rumours circulating was the disease had come from imported semen. At a public meeting last week, MPI specialist incursion investigator Tom Rawdon said he personally believed it was a ``red herring''.
Yesterday, World Wide Sires New Zealand general manager Hank Lina said MPI had confirmed there was no evidence that resistance had developed to mycoplasma in imported bovine semen.
``MPI's validation that imported semen was not the cause of the mycoplasma outbreak is bittersweet. We're naturally delighted to have this confirmation of our standards and systems, but our hearts go out to the Van Leeuwen family, who are living through a farmer's worst nightmare,'' he said.
Meanwhile, a new diagnostic test for M. bovis, developed in Australia, is being used in both Denmark and Finland to investigate the prevalence of the disease.
Dr Nadeeka Wawegama, a research fellow at the University of Melbourne who has developed the test that could detect both subclinical and clinically infected cattle, said a few other countries had also shown interest in using the test.
When contacted to ascertain the effect of the disease in Australia, Dr Wawegama said Dairy Australia confirmed in 2006 M. bovis was in some dairy herds and it was considered a ``significant'' pathogen.
Once confirmed, the infected dairy cattle were culled, as there were was no antibiotic treatment.
It was also done to prevent the spread to the herd and milk from the infected cattle could also not be used on calves, so the economic loss was ``very big'', she said.
Until now, the prevalence of M. bovis in Australia, or any other country, was difficult to achieve due to the lack of such a sensitive diagnostic test, she said.
The new diagnostic test could detect the antibodies against M. bovis bacteria produced by the cow's body.
The new test was ideal to use as a diagnostic test to understand the prevalence of the pathogen and could be used to screen cattle before they were sold or transported to new farms. Once established, the test could be used on routine testing to improve the biosecurity and prevent the spread of disease.
It had already been used as a tool to investigate the prevalence of M. bovis in Australian beef cattle in 2015.
Using almost 7500 beef cattle in 14 different beef herds across Australia, it was found 13% of the beef calves were carrying the bacteria before they entered the beef herds.
After six weeks in the herds, the prevalence of the bacteria had increased to almost 70%, showing a very high prevalence of M. bovis in the country's beef herds.
Last year, Dr Wawegama received a Dairy Australia award in the Science and Innovation Awards for Young People in Agriculture, Fisheries and Forestry.
It was to use her new test to detect the prevalence of M. bovis in Australian dairy herds using bulk tank milk samples. Currently, prevalence was estimated at about 3%, using only the PathoProof PCR test.
She has been collecting bulk tank milk from three main dairy companies and planned to estimate the prevalence of the bacteria, while also looking at the seasonal effect of the infection.
Mycoplasma bovis - which does not infect humans and presents no food safety risk - can cause mastitis, abortion, pneumonia and arthritis.
Studies suggested at least 50% of Australian dairy herds were affected by subclinical mastitis, at a cost to industry of more than $60million a year.