Q & As
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What does TB freedom mean?
In the context of the TB Plan review, ‘TB freedom’ means confidence that there are no TB infected farmed cattle or deer herds in New Zealand, and there are no infected possum populations likely to cause re-infection of livestock. Currently for possums disease freedom is defined as achieving at least 95% confidence, through a structured ‘Proof of Freedom’ process, that TB is no longer present in an area.
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What does eradication mean?
In the context of the TB Plan review, ‘eradication’ of TB is defined as having a very high level of confidence, based on modelling of data collected through programme activities over time, that TB is no longer present in any livestock, possums, pigs or deer.
Eradication is a step beyond TB freedom because it’s about a high level of confidence that TB is gone from all species of interest (livestock, possums, pigs and deer), over a longer period of time.
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Does eradication mean eradication of possums?
No – it means the eradication of TB disease, by suppressing TB vectors (possums) to low-enough density for the time required to ensure disease dies out of the possum population. Once the TB disease is gone, the possum population may recover unless control is undertaken by others.
OSPRI will still need to consider how to maintain good operational relationships with regional councils and others undertaking pest control work nationally.
What does elimination mean?
In the context of the TB Plan review, ‘elimination’ is the act of removing infection from the target population, that is, the process rather than the end result.
What happened to the objective of achieving TB freedom in livestock by 2026? That’s what it says on OSPRI’s website?
The milestone of TB freedom in livestock by 2026 was set in 2015, the last time the TB Plan was reviewed. New Zealand has come very close to that, with around 0.01 percent of herds infected (15 out of about 75,000 at 30 June 2025). However, as has been seen in recent years, there will continue to be outbreaks while reservoirs of disease remain in the possum population. It is not practically possible to achieve or maintain absolute zero herd infections until the disease is no longer present in possums.
OSPRI will update its operations, including its website, once final decisions are made following the review.
Where does the figure of 75,000 herds come from?
For the purposes of TB management, OSPRI defines a herd as ‘all cattle or deer under the day-to-day management of a single Person in Charge of Animals (PICA). This includes a single animal or a large group’.
This definition aligns with international definitions used in monitoring TB prevalence.
Using this definition, there are 75,107 herds in New Zealand, as stated in the OSPRI 2023-24 annual report.
Will ‘prioritising possum hot spots’ take the focus away from herd freedom from TB?
On the contrary, the intent is to eliminate TB from possums so that they don’t keep reinfecting herds. This will help us achieve herd freedom. Alongside this priority, OSPRI will continue management of infected herds and surveillance testing to limit the spread of infection.
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What will prioritising hot spots mean for other areas where there are still infected possums?
The programmes in other areas will continue until those areas are cleared.
Is the use of aerial 1080 necessary?
Yes. The review confirms that aerial 1080 is the optimal, most cost-effective tool for larger, ‘landscape scale’ possum control operations, such as difficult-to-access steep and remote back country and extensive areas of South Island pastoral land.
The alternative, greater use of ground control (trapping and toxins), is significantly more expensive and cannot achieve the level of coverage necessary to knock down possums in steep and difficult to access areas, potentially allowing the disease to persist in reservoirs of infected possums, from where the infection will spread again.
Are there any new technologies that could reduce the reliance on aerial 1080 and/or improve the cost effectiveness of the programme?
There is a lot of research and development underway, with a number of emerging technologies that may be useful for disease diagnosis, wildlife vector surveillance, and control practices over the next decade.
This includes pest surveillance options such as drones and thermal imaging to estimate possum numbers in less-forested areas, and advances in testing for infection.
However aerial 1080 remains the best possum control tool available to deliver rapid, effective and large-scale control over landscapes where the terrain or vegetation cover prevent reasonable access for workers on the ground.
Will the targeted testing approach come with greater risk of more infected herds?
While there would be less frequent testing, OSPRI is confident it can target higher-risk herds for testing, reducing the chances of missing an infection. Over time, as funds saved from targeting testing are used to eliminate the disease from possums, then the risk of re-infection from possums will drop.
What will happen with possum control in areas where TB has been eradicated?
Pest control carried out under the National TB Plan does deliver significant biodiversity benefits. However, the control of possums and other pests is only carried out under the Plan where control contributes to the achievement of the Plan’s TB-related objectives. As is already the case in many TB free areas, agencies with pest control roles (e.g., regional councils and the Department of Conservation) and individual landowners will develop and fund their own possum control plans and programmes.
​What’s DOC’s role in possum control?
The Department of Conservation (DOC) commits resources to possum control at priority sites to ensure the long-term survival of species and the ecosystems that support them https://www.doc.govt.nz/nature/pests-and-threats/animal-pests-and-threats/possums/
DOC also has a role in administering conservation land and in some areas works closely with OSPRI on possum control on land it administers.
There are benefits to the TBfree programme from DOC’s possum control activities, and DOC was an observer on the TB Plan review. However, TB control and eradication is not DOC’s primary focus.
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Why is there a projected shortfall after 2031?
Primarily because the previous budget forecast back in 2015 did not account for inflation.
The intent was that the amount farmers (and the Government) have to contribute would start to decline from 2031. However the impact of inflation means that there has been less money available for possum control, so the risks and infection levels have not fallen as quickly as anticipated in 2015.
What will happen to farmer levies after 2031?
It’s too soon to say. The projected shortfall is based on the modelled annual cost, including accounting for inflation going forward, but over the next few years more work will be done to confirm what the costs beyond 2031 will actually be.
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Do feral deer get infected with TB in NZ?
Yes, feral deer can become infected with TB by interaction with Infected possums in the bush. At the start of the programme (1993) when infected possums were widespread and disease levels within those populations were high, disease was found in feral deer. However, since possum control has driven the disease out of possums, there has been a corresponding drop in infected feral deer. This has been achieved without purposefully controlling deer populations as they are considered a spillover host for bovine TB.
What is the difference between a maintenance host and a spillover host for TB ?
A spillover host is an animal species that gets infected with bovine TB but cannot keep the disease going within its own population, so it dies out over time. Feral deer fall into this category along with pigs.
On the other hand, a maintenance host is a species of animal that once it has become infected with bovine TB can keep the disease cycling within its own species, without the need for re-introduction. Possums, cattle and domestic deer fall into this category.
How is disease monitored in feral deer?
All feral deer shot by hunters being sold for human consumption must have a post-mortem inspection. The meat inspectors inform OSPRI whenever a lesion suspicious of bovine TB is found and these lesions are processed in the same way as any domestic stock. There have been no reported feral deer bovine TB cases since 2022.
OSPRI is also very open to all reports from hunters of any suspicions of TB. A concerned hunter from the South Island even went so far as to produce an educational video to highlight what to look for when shooting pigs and deer.
Do feral deer maintain TB within their population in NZ?
Feral deer are considered a “spillover” hosts in NZ. Individual deer are infected by contact with TB infected possums, but don’t then spread the infection onto other deer in the feral population.
What does OSPRI do about feral deer in the NZ TB Eradication programme?
OSPRI has never actively controlled deer populations. All the research over the years has shown that by controlling TB in possum populations, then the disease would drop out of the deer population in that area as well.
Is the increasing feral deer population, a concern to OSPRI?
It is disappointing to see large numbers of feral deer in the NZ bush due to the damage that they are doing both to the bush and to farmers’ crops.
Whilst OSPRI was aware of deer coming onto farms in the Hawke’s Bay during the TB outbreak there in 2020, only possum control was instigated, and the situation was brought under control.
Why is feral deer infection a problem in other countries?
There is a longstanding recognised problem of transmission of disease from feral whitetail deer to cattle in Michigan in the USA. The problem is basically driven by hunters feeding deer to draw them to a certain area which increases the contact between the feral deer which in turn increases disease transmission within the population. It also habituates the deer to seeking out feed and so they enter cattle farms and eat out of their feed bins. The problem has been managed in recent years by fencing deer out of cattle herds.
What concerns does OSPRI have with TB infected feral deer?
The fact that deer are a much longer-lived species than possums (up to 20 years for a hind), the concern that OSPRI does have about feral deer is the low but non-zero potential for an old TB infected deer dying in the bush and being scavenged by a possum, potentially infecting that possum and restarting possum population infection in areas no longer controlled by OSPRI.
Reinfecting possum populations after control is completed has not been shown to have occurred to date but is a theoretical possibility. It is why OSPRI keeps possum populations reduced for long enough so that this risk is reduced.
Would OSPRI ever control feral deer populations?
OSPRI is funded to eradicate bovine TB from cattle and deer herds and possums. There is no evidence that feral deer directly infect domestic herds and so there are no plans for any national deer population control.
Why do domestic deer herds get infected with TB, but OSPRI are not concerned about feral deer?
Deer are farmed in domestic herds in NZ at much higher densities than feral deer are found in the NZ bush.
The higher density of stock, also held in close proximity with each other in handling sheds, enables the transmission of infection from one animal to another in domestic herds. Evidence of feral deer to feral deer transmission has not been seen in NZ.
Why are feral pigs and deer considered a spillover host in New Zealand?
It is known that wild pigs and deer become infected in the wild by contact with infected possums. Pigs by eating possum carcases of animals that have died of TB and deer with interaction with live TB possums. Both species are considered spillover hosts in NZ. Research over many years has shown that prolonged possum control driving the prevalence of disease down in possums, results in the reduction of disease in wild pigs and deer.
Why when TB in pigs and feral deer are a problem to domestic herds in other countries is it not an issue in New Zealand?
Three reasons:
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The density of the pigs and feral deer in NZ is low when compared against other countries,
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Many years of possum control has resulted in a low TB disease prevalence within those species in NZ and,
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the opportunity for the wild pigs and deer to interact with domestic stock in NZ farms is much lower than overseas.
In Michigan, deer hunters feed the wild deer to encourage them into areas where they want to hunt. This habituates the deer to eat feed that they would not usually encounter. They then seek out this food on cattle farms in the area. Because they are now eating out of feed bins used by cattle there is a direct connection between the wild deer and cattle. By fencing deer off the properties and away from feed bins the problem has been managed.
In Spain, it is hypothesised that the congregation of wild pigs and cattle at watering holes appears to be the mechanism of spread.