The farming industry's investment in TB eradication is proving effective, allowing reduced cattle and deer testing requirements in many areas.

From March 1, reductions to Disease Control Areas will affect 2.3 million hectares and nearly 7400 herds, resulting in 289,000 fewer TB tests for herds. That's a lot of time and expense saved.

OSPRI (Operational Solutions for Primary Industries) is a non-profit company established in 2013 when the Animal Health Board and NAIT (National Animal Identification and Tracing) merged.

It administers regional disease control areas (DCAs) throughout New Zealand, each with different TB testing requirements and stock movement restrictions depending on the risk of TB being transferred from infected wildlife (mainly possums) to cattle and deer.

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As OSPRI's Dr Stu Hutchings told the Future Farms conference last month, significant progress has been made in reducing tuberculosis in livestock. In June 2000 there were nearly 700 infected deer and cattle herds spread around most parts of the country; today there are only 41, with clusters in the South Island and a few infected herds in the North Island.

Progress has come more quickly than once anticipated, and this gives confidence the agency's strategy is realistic: to have all cattle and deer free from TB by 2026; to have TB out of possums by 2040; and biological eradication of the disease by 2055.

When tuberculosis is found in a farmer's cattle or deer herd, the economic and social impact can be significant, Dr Hutchings said.

"They're put into a quarantine, they can't trade any more, it impacts directly on their ability to sell livestock to other farms.

"In the communities where they live and work, questions are asked along the lines of 'what's gone wrong here? What have they done? Often it's nothing they have done at all. They may have brought in animals with undetected disease, or their farm happens to be in a location where there are possums with TB."

The tuberculosis bacteria that threatens livestock is in the same family as human TB. It can cause significant infection in lungs, lymph nodes and body cavities of any mammal but OSPRI concentrates on deer, cattle and possums.

Transmission to farmed animals is from possums; they're the disease maintenance hosts or vectors.

"Often when they're sick, they stagger out from the bush into paddocks. Cattle and deer are really inquisitive and will sniff them [taking in the bacteria]. Deer will actually pick them up and toss them around. The TB is then spread cattle to cattle, deer to deer, on the farm."

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Two-thirds of OSPRI's revenue is spent on possum control, which has major crossover benefits for native birdlife.

If the disease is found on a farm during testing, a quarantine and continual test/slaughter programme is maintained.

"We need two clear herd tests at least six months apart before we call that farm clear," Dr Hutchings said. "We also have movement restrictions in some regions where there is high TB prevalence. Any farms in those areas have to do TB testing prior to moving any livestock out of that locality."

The new focus will be grounded in risk. The testing requirements will be based on three things: the farm's location, the herds' TB history, and whether the farm has brought in animals from risk areas.

The focus is on getting rid of the disease from possums, we're not going to be able to eradicate all the possums - a key point.

"All this means fewer tests for low risk herds, and post-movement testing for those with the greatest risk of infection," he said.

Future possum control work will be based on proximity to livestock, the extent of possum infection and how difficult it will be to stamp out the disease.

"The focus is on getting rid of the disease from possums, we're not going to be able to eradicate all the possums - a key point. We need to get their numbers down until the TB disappears."

Dr Hutchings said "strong buy-in" was required from farmers to keep NAIT and herd movement records up to date. A lot of work is going into monitoring where there has been infection.

"We trace back for any cattle or deer that have come into the herd or gone out again. Movement is one of the biggest factors in transmission of the disease, and [our work is] more around individual animals rather than geographical areas.

"It's important we have good buying decisions, so people understand the risk of buying animals [from disease control areas], not just chasing the cheapest dollar."

Asked how traceability improved returns, Dr Hutchings said NAIT and TB testing was used to work out where the disease had come from, "so we can tailor our efforts to manage and get rid of it in a lot quicker time".

"The whole area of traceability from a farm management, food safety and biosecurity perspective is a much bigger story, one fundamental to us as a country and one where we have a lot more work to do."