The Ministry for Primary Industries says its Mycoplasma bovis programme, in consultation with industry, will continue screening bulk tank milk, with a few modifications to the regime that will improve its ability to identify infected farms and support the eradication of Mycoplasma bovis.

National screening will be conducted monthly, kicking off on July 1, and will continue indefinitely.

MPI said the Spring Surveillance Programme proved extremely valuable as it provided assurance that infection was not widespread outside already identified farms.

It also identified a small, additional number of infected farms not found through animal movement tracing, as well as highlighting the ability of the ELISA test to produce a very low rate of false positive results.

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It said ongoing screening of bulk tank milk samples nationally might identify infected herds otherwise undetected due to incomplete and inaccurate movement records, and might identify infected herds faster than the tracing of animal movements, as those movements could only be traced once the source Confirmed Property was found.

A summary of what's changing:

• Going forward only the ELISA testing method will be used – it has proven to be a much better screening tool than the PCR test. Farmers will be notified of all ELISA-positive test results within 2 weeks of testing.

• Farms with an ELISA-positive test result will be placed under a Notice of Direction (a NOD) restricting cattle movements (a NOD) while sampling and testing of the herd is carried out to determine the disease status of the farm.

• ELISA-negative test results will be regularly reported to farmers. The programme is working with industry to explore automated ways to report negative results. An update on the format and frequency of this reporting will be provided before July 2019.

It was important to emphasise that bulk tank milk ELISA-negative test results did not prove absence of infection, nor did a positive test result prove that a herd was infected. It was an indication only, and further testing needed to be carried out.

"Unfortunately, there isn't a single 'yes or no' bulk tank milk test for M. bovis, so it's important that we continue regular screening for at least the next 12 months," said Geoff Gwyn, director of the M. bovis Programme.

"The true M. bovis infection status can only be determined by on-farm testing of the herd."

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Previously the programme had not used the bulk tank milk ELISA to screen autumn calving herds in early lactation. Testing this milk was a valuable opportunity to possibly identify additional infected herds prior to the 2019-2020 milking season. Bulk tank milk samples had been stored fortnightly since April 15, and testing of these stored samples was now under way.