Bovine Tuberculosis (bTB) – a wicked problem

Ireland has seen a renewed and worrying rise in the number of bovine Tuberculosis (bTB) cases in recent years. From a low point of approximately 3% of the national herd being affected in 2015, numbers have steadily risen to over 6% in 2025 – a level not seen since the early 2000s.

“IT’S LIKE SOMEONE JUST HIT YOU HARD IN THE STOMACH”

DAIRY FARMER ON DEALING WITH bTB

Why is it so complicated to solve?

Eradication of bTB in Ireland is exceptionally difficult due to a complex, multi-host infection cycle, high-density cattle farming, and increasingly a resurgence in infections.

The key issues are:

• Wildlife reservoir: bTB is endemic in the wildlife in the country, with badgers identified as a major reservoir and vector of the disease.
• Diagnostic issues: current diagnostic tests (the skin test) do not identify all infected animals, allowing undetected spreaders to remain in herds. The skin test also can’t distinguish between animals that are vaccinated from those who are infected. So most international laws (including EU directives) explicitly prohibit the vaccination of cattle because it causes them to fail the standard skin test used to certify beef and dairy as safe.
• Environmental Survival: The bacterium which causes bTB, Mycobacterium bovis (M. bovis), can survive, in the right conditions, for 6 months or longer, leading to infection risks from contaminated pasture and water. It particularly likes damp, cold and dark conditions, meaning it can remain viable in the environment for several months, particularly in soil, faeces, or slurry.
• Cattle Density and Movement: Since milk quotas were removed in 2015 the number of dairy cows has increased by over 30%. It’s worth noting that some reports indicate over 1,000 dairy farmers actually exited, but the remaining farms have become much larger, more intensive, and more productive. Infections are mainly caused by infection remaining in the herd from a previous bTB episode, purchased infected animals, infection from wildlife and direct or non-direct contact with neighbouring cattle. So increased cattle density will increase the likelihood of outbreaks.

Badgers – A Resevoir For Tuberculosis

I love badgers. There are a couple of them that shuffle around the green areas here at night. They eat everything, including many pests. So I don’t want to turn anyone against badgers. They are also a protected species in Ireland.

That said, badgers can carry and transmit M. bovis. They are part of the multi‑host system that sustains bTB in some areas. Control of wildlife reservoirs, preventing the spread of Tuberculosis from cattle to badgers, badger to badgers and from badgers to cattle, is the focus of the national strategy.

This strategy uses a combination of culling and vaccination to restrict the spread. In areas of high incidence of bTB badgers are removed and culled. In other areas, healthy badgers are vaccinated in hopes of building up herd immunity within the species and ending the need for culling.

The vaccination programme is more of a long term solution. It is controversial as some farmers feel that culling is a more effective strategy. But research has found that 80% of culled badgers are healthy and free of Mycobacterium bovis. And if herd immunity for TB can be achieved for badgers here, which only a vaccination programme can achieve, then that would seriously help reduce the problem of bTB.

Sika deer are also affected – and this can be an issue in Wicklow. When necessary deer in high incidence areas have been culled. Currently deer are not part of a vaccination strategy.

Why Not Vaccinate The Cattle?

There is a vaccine for bovine Tuberculosis which uses a weakened version of the BCG strain of the bacterium. A cow injected with this safe attenuated strain, produces the antibodies needed to fight the disease. So if they do get infected with M. bovis their immune system is ready to stop it. Their immune system now recognises and reacts to bTB antigens.

The common test for TB, the skin test, involves injecting a Purified Protein Derivative, a tuberculin antigen, just under the top layer of skin. If the disease is present in the animal, its immune system will recognise the bTB antigens producing antibodies that react leaving a visible sign on the skin at the injection site.

There are two problems with this test for cattle. It misses between 20 – 25% of cases. And … it cannot distinguish between a vaccinated cow and an infected one.

IS A DIVA (DIFFERENTIATING INFECTED FROM VACCINATED ANIMALS) TEST ON THE WAY?

There are a number of initiatives around the world trying to find a solution to this problem. One of the most promising is happening right on our doorstep.

The UK is currently running Phase 3 testing (the final phase of on-farm field trials) of a bovine BCG vaccine with a DIVA companion test. Phase 3 testing is expected to complete this year.

For the DIVA test to be accepted by the WOAH, the World Organisation for Animal Health, it must demonstrate extremely high specificity, generally exceeding 99.85% to 99.9%. This ensures that less than 3 in 1,000 uninfected animals test falsely positive, maintaining the integrity of TB-free status.

HOW DOES THE DIVA TEST THEY’RE TRIALING WORK?

It uses a skin test that checks for specific antigens that are present in wild bovine TB but are missing from the BCG vacccine; ESAT-6, CFP-10, and Rv3615c. The BCG vaccine lacks the genetic information needed to create these proteins. So the immune system of a vaccinated cow won’t react to the test, whereas the immune system of an infected cow will recognise these antigens and give a positive result to the test.

This DIVA DST-F (Defined Antigen Skin Test) has shown very promising results so far. So there is reason to be cautiously optimistic.

CAUTIOUSLY OPTIMISTIC?

One thing researching this topic has taught me is that TB is one tricky wee demon. So maybe expect the worst and hope for the best? But honestly, this does seem very promising. WOAH recognised the significant progress made and supports the current UK trials as a major breakthrough toward international validation.

But even if the final stage of testing is successful, a bTB vaccine rollout is still a few years off because it’s going to require acceptance by a number of international organisations, including the WOAH. And there will need to be legislative changes to allow for such a vaccination programme in the EU.

The Weather’s Role

It has been a brutal start to the year for Irish farmers. If rising bTB rates hasn’t been a cause of concern, the relentless rain certainly has. Saturated ground can make the daily job of farming feel like an uphill battle.

Although not the main cause of the recent spike, weather impacts bTB in specific ways:

• Damp, dark, cold weather creates the perfect environment for M. bovis: As I mentioned above, cool, moist, and dark conditions allow the bTB-causing bacteria to survive for months longer in the environment, in soil or slurry, compared to the weeks it can survive in warm, dry and sunny conditions.
• Research shows that areas experiencing high rainfall are strongly associated with higher bTB rates. It has been suggested this may be because harsh weather drives cattle to seek shelter together, increasing animal-to-animal contact.
• Wet weather can increase the prevalence of liver fluke. The liver fluke parasite can suppress its host’s immune system, making the cow more suspectible to infections, like bTB. And a suppressed immune system also makes the results of the skin test less reliable.

How Agroforestry Can Help

Agroforestry is the intentional, sustainable integration of trees and shrubs into crop and animal farming systems to create environmental, economic, and social benefits. It enhances biodiversity, improves soil health, provides shade for livestock, and boosts carbon sequestration.

Using trees and fencing to create riparian buffers with vegetated strips along watercourses, is one of the most effective ways to break the transmission cycle of bovine TB while simultaneously managing flood risks.

Specifically agroforestry and riparian buffers can help prevent the spread of bTB in the following ways:

1. BREAKS THE BADGER-CATTLE LINK

   Waterways are wildlife highways – badgers use riverbanks and streams to travel and mark their territory.

   In a standard field, cattle often graze right up to the edge of a stream or hedge. This is where they are most likely to come into contact with badger urine or faeces, which carry the M. bovis bacteria.

   By sacrificing a 5 – 10 metre strip along the water and planting it with dense vegetation and/or trees, a physical barrier is created.

   A robust riparian buffer usually involves double fences. The two fences prevent nose-to-nose contact between livestock and wildlife, significantly lowering the risk of a TB breakdown.

2. TREES MAKE FOR DRIER GROUND WHICH MEANS LESS BACTERIA SURVIVAL

   Trees effectively dry out the soil in adjacent grazing fields. The soil under trees acts more sponge-like. Tree roots create channels or pores in the soil that allow water to drain deeper into the ground rather than pooling on the surface. Also, fallen leaves and root exudates build soil organic matter, improving the soil’s texture and its sponge-like abilities. This also improves the nutrient profile of the soil. Tree canopies can also act like a sort of “umbrella with benefits”, intercepting and evaporating a portion of rainfall before it ever reaches the ground. And trees drink up groundwater, drawing it up from the soil, and releasing it as water vapour into the atmosphere through their leaves.

   In a waterlogged muddy open field or in the muddy bank of a stream, M. bovis bacteria can easily survive. Trees create conditions for drier, well-drained pastures that are much less hospitable to the bacteria.

3. REDUCES IMMUNE STRESS

   A cow’s immune system is its primary defense against TB. High stress levels make cattle more susceptible to infection.

   Trees planted as part of a riparian buffer act as windbreaks. In the harsh Irish wind and rain, cattle behind a shelter belt have lower cortisol levels and maintain their body temperature more easily.

   Drier land supports more nutritious grass ensuring the herd is in peak physical condition to fight off potential infections.

AGROFORESTRY CAN ALSO HELP WITH FLOODING

The same strip of land, the riparian buffer with dense vegetation, used for TB protection acts as a flood attenuation zone.

Tree roots, and the roots of other vegetation, can effectively knit the riverbank together, preventing slumping or erosion during periods of high water.

When a river bursts its banks, surrounding trees and thick vegetation can slow the flooding water down. Slower water has less energy and causes less damage to downstream infrastructure.

Another benefit is that trees help manage dairy runoff by acting as natural filters and buffers, significantly reducing nutrient pollution (nitrogen, phosphorus) and fecal bacteria entering waterways.

Supports For Agroforestry And Riparian Buffers

There are a range of EU and national supports to establish silvopasture (agroforestry that intentionally integrates trees, forage and livestock) and riparian buffers that reduce runoff and flooding while improving landscape connectivity and biosecurity, helping to limit the spread of bTB. The Agri‑Climate Rural Environment Scheme (ACRES) offers payments and non‑productive investment options for tree‑planting, riparian actions and habitat measures. The Forestry Programme 2023–2027 and specific agroforestry grants provide establishment grants, annual premiums and technical supports for on‑farm tree integration and shelterbelts, while Teagasc and the Irish Agroforestry Forum supply practical guidance, design templates and advisory services to help farmers combine grazing with tree planting in ways that protect watercourses and create wildlife corridors.

WHERE TO GET MORE INFORMATION AND APPLY

• ACRES (Agri‑Climate Rural Environment Scheme) — official scheme details, measures and application guidance.
• Forestry Grants and Schemes (DAFM) — Forestry Programme 2023–2027, afforestation and agroforestry grant rates.
• Teagasc Agroforestry — practical guidance, case studies and technical notes on silvopasture and riparian planting.
• Irish Agroforestry Forum — funding summaries, business models and farmer resources for agroforestry projects.

Bovine Tuberculosis – A Wicked Problem – But A Solution May Be On The Way

The increased incidence of bTB in recent years is a source of concern for farmers. It is encouraging that a vaccine and DIVA test is in the final stage of testing. Hopefully that will go well. But it likely will still take years to rollout.

Wet weather and mild winters are a perfect breeding ground for M. bovis. Experts say climate change is going to make Ireland even wetter…  Strategic use of land management with agroforestry could help prevent the rise and spread of bTB. It also can mitigate flooding. There are supports to help farmers adopt agroforestry – and perhaps more needs to be done to help farmers avail of these supports.

I stumbled on this topic over the weekend and I found it really interesting. So I just thought I’d share what I found. Here’s hoping our farmers get a break – and the weather seriously improves!