Bovine tuberculosis (bTB) remains one of the most persistent animal health challenges in Great Britain. At the heart of national surveillance is the Single Intradermal Comparative Cervical Tuberculin (SICCT) skin test, in use for almost a century and still the cornerstone of detecting infection in cattle and other mammals, worldwide. But while the science behind the test is robust, the tools used to carry it out have changed remarkably little; the callipers and approach we use today would have been recognised by veterinarians and farmers working almost 100 years ago.
This year, a unique collaboration between the Animal and Plant Health Agency (APHA), the Roslin Institute and the UK Agri‑Tech Centre, set out to explore whether innovation in a single piece of equipment, the humble handheld calliper, could deliver a significant positive impact for bTB control.
The Roslin Institute delivered a rigorous literature review, identifying where improved measurement could enhance diagnostic consistency and where constant‑pressure devices may offer most benefit. The UK Agri‑Tech Centre led market analysis and stakeholder engagement activities, identifying promising technologies from other industries and feasibility considerations for adaptation into veterinary use. APHA teams brought their expertise in managing bTB, ensuring the work aligned with regulatory requirements and practical realities on the ground.The collaboration has resulted in a compelling, evidence‑based blueprint for next‑generation testing tools that could significantly improve national bTB surveillance.
Why focus on callipers?The SICCT test relies on precisely measuring the pre-injection skin thickness at two injection sites on the neck and then measuring any increase in skin thickness after a 72-hour period. Although the current protocol is clear and trusted, both scientific literature review and stakeholder engagement activity show that:
Skin‑fold measurements are vulnerable to human variability. Testing conditions are highly variable with visibility, weather, handling facilities and cattle behaviour all influencing measurement accuracy. Manual callipers introduce opportunities for error and require transcription into software systems. As new tuberculin reagents are being developed, future skin reactions may be smaller, demanding even greater precision.Research from Roslin highlighted the potential value of more accurate and consistent measurements, especially if callipers could apply constant pressure, reducing operator‑related variation. Meanwhile, the market analysis demonstrated that other sectors (such as forestry and manufacturing) already use digital, memory‑enabled instruments that could inspire veterinary adaptations.
Together, this pointed toward a clear opportunity: a purpose‑built, digitally integrated, pressure‑controlled calliper fit for use under farm conditions.
Listening to the people who test cattle every dayA defining feature of this project was its commitment to co‑design. Through in‑depth interviews and a sector‑wide workshop, vets, Approved Tuberculin Testers (ATTs), auditors, farm consultants and industry bodies shared frank, detailed insights into the realities of using handheld callipers on farm. Key insights included:
1. Accuracy comes firstStakeholders across the industry stressed that any new device must demonstrably match or exceed the accuracy of current tools and be considered fit-for-purpose by APHA.
2. Current calliper models can be difficult to use
Challenges identified included: difficulty reading calliper measurement scales in poor visibility, requiring both hands to operate the calliper which may present a safety risk with fractious cattle, fatigue and strain during high‑throughput testing and calliper wear‑and‑tear, affecting readability and calibration.
3. Data handling needs to improveManual recording, often on paper, potentially in the rain, was universally seen as a risk to data quality. Stakeholders repeatedly called for automated data capture, improved integration with herd management software and better access for farmers to their own results.
4. There is strong appetite for innovationStakeholders expressed high interest in piloting new tools, including digital callipers, constant‑pressure mechanisms, EID integration and real‑time data transfer. They also highlighted that some existing calliper models (e.g. linear scale callipers) already exist which may address some of the concerns and issues raised in terms of accuracy.
5. Adoption depends on trust, training and costStakeholders agreed a new device must be affordable, robust, easy to clean and disinfect, and rolled out with clear communication and practical training.
A shared vision for a next‑generation calliperFrom the workshop’s co‑design activities, a future-ready calliper began to take shape.
Photo from the stakeholder workshop showcasing some of the different callipers used already, along with other equipment and forms that are required for TB skin testing.Stakeholders prioritised:
Better design and ergonomics: Single‑handed operation, ambidextrous, compact and rugged, clear digital display visible in sunlight and rain, easy to disinfect, waterproof and shock‑resistant Improved measurement capability: Pressure‑sensitive or constant‑pressure mechanism, improved reading consistency between operators, accuracy suitable for cattle and other species, compatibility with potential future skin test reagents Integrated data capture: Onboard memory or Bluetooth connectivity, automatic pairing with animal ID, seamless export to commercial software and APHA systems, local data storage for low‑signal areas Improved data sharing and transparency: Automated reporting to APHA, farmer‑friendly summaries or dashboards, support for risk‑based herd health planningWhat emerged was a shared ambition, not just for a new calliper, but for a modernised bTB testing ecosystem with secure, standardised digital reporting and reduced administrative burden for testers.
Laying the foundations for future testing innovationWhile the project did not set out to select a preferred device, it has established:
What calliper features frontline testers value most Where the current calliper models fall short How improved consistency could reduce operator variability What would be required to ensure bTB tester buy‑in How data integration could transform efficiency and accuracy in reportingImportantly, it also confirmed that any transition to a new technology must be carefully validated, well‑communicated and sensitive to real‑world constraints.
The next steps may include prototype development and piloting, in addition to exploring how data from digital callipers could feed directly into existing bTB reporting systems.
"The collaborative nature of this project enabled us to examine skin test measurements holistically, without narrowing the problem to a single dimension. It was particularly encouraging to see consistent insights emerging across the different streams of work, giving us confidence in how we will support the next steps to improve the practicality of skin testing."
Dr. Camille Harrison and Susanne Frost, APHA
"This study provides a clear roadmap for modernising the bTB skin test, but success will depend on coordinated action. Aligning technology development with policy, funding and national implementation will be essential to ensure consistency and build long‑term confidence in surveillance outcomes. With the right support, we can deliver a more accurate, transparent and future‑ready testing system."
Dr Bethan John, Animal Health Specialist, UK Agri‑Tech Centre
"The recent update to the bovine TB eradication strategy emphasizes the importance of improving diagnostics and removal of hidden infection in cattle. While much of the attention is focussed on development of new technologies, the simple improvements to manual callipers considered in this project could reduce inter-operator variability, improve the sensitivity of the test and facilitate the use of test measurements to improve herd management. However, it must also overcome potential issues of device robustness and variability in readings that may be due to differences in immune response or cattle skin thickness between breeds. These challenges are worth overcoming; the SICCT remains central to bTB control, and any improvement in the precision of skin measurements and reduction in the potential for human error are important steps towards more effective disease control and greater trust in the testing system."
Prof Rowland Kao and Prof Fiona Houston, Royal (Dick) School of Veterinary Studies, Roslin Institute & School of Physics and Astronomy
seen at 09:53, 13 May in APHA Science Blog.