Research that uses animals follows the internationally recognized 3 Rs principles: replacement, reduction, and refinement. For replacement, U.K. and E.U. law states that protected animals must not be used in science unless alternatives are unavailable. This principle is further backed by institutions such as U.K. Research and Innovation, the largest investor of public money in research and innovation, whose policy is to fund animal research only when no “scientifically acceptable non-animal alternatives” exist. Moreover, replacement is built into the U.K.’s three-tier licensing system for animal experimentation. Each tier, including the research project itself, the location where it takes place, and the person who conducts it, requires a license. The replacement principle is a condition of these licenses.

Replacement Isn’t Working Right Now

Despite the emphasis on replacement, it’s generally acknowledged by U.K. institutions and researchers that this principle isn’t well applied. Reasons include a lack of knowledge and confidence, inadequate guidance and training, and barriers within existing processes.

The problem is compounded by the fact that research projects are reviewed only after funding has already been given and the use of animals has already been decided. Alternatives such as cells and tissues, computer-based models, and human volunteers are therefore likely to be missed. Not only does this cause unnecessary harm to animals, it also damages public trust in science.

Although the license guidance in the U.K. (and E.U.) requires researchers to explain how they’ve applied the replacement principle, there’s no minimum requirement for what information must be provided. Researchers are asked to conduct systematic reviews using animal-based literature. While these reviews can offer some insights, there are many limitations to this approach. They require considerable time and resources, and because they’re based on research that uses animals, they’re unlikely to identify alternatives. This suggests that, on its own, a systematic review is impractical for finding replacements.

Helping Replacement Work Better

The authors of this paper, who work for the U.K.-based charity Replacing Animal Research, suggest that the replacement principle be applied at the start of the research planning process instead. They propose a simple checklist (and accompanying guidance) to be integrated into existing procedures. This “replacement checklist” was created in consultation with researchers, animal ethics committees, and animal protection organizations.

The checklist consists of the following six questions to guide researchers in their search for non-animal alternatives:

1. What? Studies that use non-animal methods won’t necessarily be tagged with terms like “replacement” or “alternative.” Instead, researchers should search for combinations of subject-specific terms and keywords focusing on specific techniques that avoid animal use (e.g., “in vitro,” “model,” “assay”).
2. Where? Researchers shouldn’t rely on a single data source. They should search different databases as well as non-traditional sources of information such as gray literature (e.g., preprints, government documents, policy papers).
3. When? Given how rapidly non-animal technologies are developing, it’s important for searches to be conducted regularly. Researchers should track the dates of their searches as well as the publication dates of their papers to show that they’re keeping up with the latest developments.
4. Who? Expertise in non-animal alternatives can be found in a variety of places — even in online discussion forums and on social media. Researchers should reach out to peers, networks, and organizations across the world for advice on opportunities for replacement.
5. How? Searches are often iterative — they’re refined as new combinations of search terms and filters produce better results. Researchers should record their search methods, such as the specific search strings they used.
6. Why? Once non-animal methods have been identified, it’s essential to evaluate their suitability for meeting the research goal in question. Researchers should explore the benefits and drawbacks of each method to justify their decision to either adopt or reject it.

Answering these questions will also demonstrate to animal ethics committees and funders that the researchers have done their due diligence in considering alternatives to animal use. This information should therefore be easily understood by non-specialists, and could even be shared with relevant institutions to avoid unnecessary duplication in the future and support an open culture of research practices. The authors also encourage the use of artificial intelligence wherever helpful.

Although the checklist can help researchers better apply the replacement principle, it’s important to acknowledge that it won’t end the use of animals in science. This is because other factors may prevent alternatives from being adopted, such as a lack of funding, training, or equipment to use other techniques.

In sum, the replacement checklist supports institutions, funders, and reviewers (whether specialists or not) to better evaluate whether researchers have thoroughly explored non-animal alternatives. It also identifies any missing information and helps researchers to better understand what’s expected of them and show they’ve met the legal requirements for replacement. By asking researchers to perform an exhaustive search for alternatives, it may also encourage them to avoid using animals altogether. Ultimately, the replacement checklist should provide all stakeholders with greater confidence in the research process.