Guest blog by Lauren Mason, MultiSci PhD candidate at Imperial College London

As part of my PhD programme, I had the opportunity to pause my research and intern with an organisation outside my university. As someone who cares about both science and animals, I was drawn to Replacing Animal Research as soon as I came across their work and mission. I care about good science, but I also believe scientific progress doesn’t have to happen at the expense of animal suffering, especially not at the scale we currently see in the UK and around the world.

I was also curious about the relationship between science and policy. In conversations with other PhD students, I’d noticed a recurring concern about “researching into the void”, which refers to a worry that our research might never have any real-world impact. Most of my time in my PhD is spent generating and analysing data, but I wanted to understand how evidence can be used to shape decisions beyond the lab. So, I was thrilled when I reached out to Policy Officer Jessie and received such an enthusiastic response about the possibility of an internship project.

Where could replacing animal ‘models’ have the greatest impact?

Luckily, it’s a very exciting time to be exploring the policy landscape of animal use in science! Following the release of the UK Government’s strategy to replace animals in science, there is growing attention on how the ambition to replace animals in science can actually be achieved. Given the current scale of animal use in research, replacing every model at once isn’t realistic. In many research areas, further research, funding, and a willingness to overcome cultural norms will be needed before animal ‘models’ can be fully phased out.

This raises an important question: how do we decide which models should be prioritised to accelerate their phasing out?

One way to approach this is to look for animal ‘models’ that meet three criteria:

• First, they cause severe suffering to animals.

• Second, they involve a substantial number of animals.

• Third, there is evidence that the model has limited translation to humans.

If a model meets all three criteria, then the expected benefits are less likely to outweigh the harms caused to animals, and the case for prioritising replacement becomes particularly strong.

Where is severe animal use concentrated in biomedical research?

We decided to focus on biomedical research because, although the Government’s strategy emphasises regulatory testing, most experimental procedures are conducted for basic or translational and applied research (Home Office, 2026). I wanted to understand where severe animal suffering is concentrated in this landscape, and whether the burden of suffering associated with some animal ‘models’ meant that they should be prioritised for replacement funding, or phase-out planning.

To do this, I mapped how animals are used in UK biomedical research by analysing publicly available non-technical summaries of project licences. These summaries are intended to provide a plain English overview of the aims, expected harms and benefits, animal numbers, and how researchers plan to apply the 3Rs. I focused particularly on project licences where animals were expected to experience “severe” procedures, and tried to identify which diseases, species, procedures, and models were responsible for that burden.

One of the clearest findings was that severe animal suffering is not evenly distributed. Instead, it is concentrated within a relatively small number of disease areas and animal ‘models’. The specific disease areas that stood out as major contributors to expected severe animal use were:

• myocardial infarction and ischaemic cardiac injury,

• tuberculosis, and

• multiple sclerosis.

Mice were used across many disease areas, while zebrafish also contributed substantially to the burden in some high-volume project licences.

 

This figure shows where expected severe animal suffering is concentrated across different areas of biomedical research, where each bar represents a disease area. The larger number at the end of each bar is the estimated number of animals expected to experience severe procedures, while the smaller number shows how many project licences they appeared across. Some species were used in such small numbers that their sections of bars aren’t visible at this scale.

Looking more closely at three animal ‘models’

I then looked in more detail at three disease-model pairings:

• middle cerebral artery occlusion as a model of ischaemic stroke,

• experimental autoimmune encephalomyelitis as a model of multiple sclerosis,

• coronary artery occlusion as a model of myocardial infarction and ischaemic cardiac injury.

These models were selected because they combined substantial severe animal burden, repeated use across multiple project licences, and were sufficiently well-defined and researched model families to allow closer assessment in the scientific literature.

Across all three disease-model pairings, we saw a similar pattern. While each model has contributed to scientific understanding, each also has serious limitations when used to predict whether treatments will work in humans. This suggests that supporting research to develop human-relevant alternatives to these animal ‘models’ could save many animals from severe suffering and improve the likelihood of developing treatments that benefit patients.

Where transparency is lacking and why it matters

The project also revealed important problems with transparency. Although there have been improvements in the information available about the use of animals in science in the UK, public-facing information remains limited.

Beyond the annual Home Office statistics, non-technical summaries are one of the only publicly available sources that describe what animals are being used for at a project licence level. Yet in practice, it was often difficult to determine which specific models were responsible for severe suffering, how many animals were affected, or which species were expected to experience which harms. This lack of clarity undermines one of the central purposes of non-technical summaries, which is to make information about animal research accessible to the public and improve transparency.

This matters for several reasons:

• Patients and the public should be able to understand what animals are experiencing in research carried out on their behalf, often using public funding.

• Researchers, funders, and policymakers need clear information to identify where replacement efforts would have the greatest impact.

• Organisations such as Replacing Animal Research need transparent data to scrutinise the research landscape and hold government commitments to account.

If severe harms cannot be linked to specific models, procedures, and species, it becomes much harder to make evidence-based decisions about replacement priorities.

What I’m taking away from my internship experience

As I’m coming towards the end of my internship, I can honestly say I’d wholeheartedly recommend an internship with Replacing Animal Research to other PhD students. I was initially a little bit worried that an online internship might feel isolating, but instead I have felt so genuinely welcomed by a group of kind, compassionate, and very cool people who are doing such important work to make science better for both humans and animals.

If you’re a PhD student with an interest in understanding how you can use your scientific background to make a difference for animals, this is a wonderful place to be. I’m leaving feeling optimistic, inspired, and excited about how I can use my experience as a researcher to contribute to a kinder and more effective research system.