The 3Rs of Animal Research are Reduction, Refinement, and Replacement.

The 3Rs were conceptualized by William Russell and Rex Burch in The Principles of Humane Experimental Technique, first published in 1959. Since then, the principles of Reduction, Refinement, and Replacement (the 3Rs)* have guided thinking, practice, and regulation of humane research animal use.

While they have been a helpful framework for the past 70 years, the 3Rs represent the beginning, not the end, of humane laboratory animal science. Though we firmly believe that the 3Rs continue to serve an essential role, we aim to expand upon these principles. Modern research presents innovative opportunities to go Beyond3Rs, which can improve the welfare and validity of animals as research subjects.

Below, we take a closer look at each "R" and how we can go Beyond.

"Reduction means reduction in the numbers of animals used to obtain information of a given amount and precision."

— Russell and Burch, The Principles of Humane Experimental Technique (1959)

What is Reduction?

In other words, Reduction means using the least amount of animals needed to conduct an experiment that is robust, reproducible, and truly adds to the knowledge base.

How can we go Beyond?

Going Beyond Reduction involves viewing animals as patients and prioritizing scientific rigor in conduct and reporting of animal studies. We can go Beyond Reduction by:

Applying principles of human clinical experimental design and analysis (e.g., use of randomization, heterogenization, and blinding).
Using appropriate modern statistical analyses to reduce the number of animals needed to find meaningful results.
Including and accounting for individual differences, so that we can see a wider range of phenotypes and responses to treatment.

This has far-reaching implications for human health — one major reason why animal experiments fail to translate to humans is because they do not account for natural variation within the population. Improving generalizability of results can increase the likelihood that animal use will yield benefits which translate to humans.

"Refinement means any decrease in the incidence or severity of inhumane procedures applied to those animals which still have to be used."

— Russell and Burch, The Principles of Humane Experimental Technique (1959)

What is Refinement?

In other words, Refinement refers to any methods which minimize the pain, suffering, distress or lasting harm that research animals might experience.

How can we go Beyond?

Many refinement techniques focus on pain management and minimizing negative physical experiences during experiments. Going Beyond Refinement acknowledges that animal welfare science is an evolving discipline, and we now have more evidence-based strategies to make positive impacts on animal health and psychological well-being. These strategies can be applied throughout an animal's entire life in research, rather than only within an experiment. We can go Beyond Refinement by:

Devoting resources to implementation of Refinement strategies (e.g., having dedicated staff for animal welfare and behavior who stay informed on current research).
Providing species-appropriate environmental enrichment that meets an animal's needs and provides opportunities for them to make choices and have positive experiences.
Promoting a culture where we always strive to improve (e.g., performing ongoing assessments of programs, and changing practices when a better way to do something is discovered).
Recognizing that in addition to improving animal experiences, implementing Refinements to housing and husbandry can improve research quality.

"Replacement means the substitution for conscious living higher animals of insentient material."

— Russell and Burch, The Principles of Humane Experimental Technique (1959)

What is Replacement?

In other words, Replacement means avoiding the use of animals in an experiment where possible and using a non-animal method instead. Many non-animal methods, such as cell cultures and computer modeling, are under development around the world.

How can we go Beyond?

Going Beyond Replacement involves reconsidering two key concepts in Russell & Burch’s original discussion: relative vs absolute Replacement, and higher vs lower organisms.

Russell and Burch discussed “relative” and “absolute” Replacement as two distinct categories. Going Beyond3Rs involves a more nuanced view which considers Replacement as a spectrum.

Thinking of Replacement as a spectrum from "soft" to "hard" emphasizes that any relative movement towards absolute Replacement is beneficial, even if absolute Replacement is not possible (e.g., in behavioral studies). In fields of research that continue to require animal models, hard replacement methods can be useful to identify research targets before soft replacement methods are employed to test the most promising candidates.

Additionally, the original 3Rs concept of replacing “higher” with “lower” organisms relies on the assumption that there is a “ladder of life” from “lower” to “higher” organisms, and that this is somehow meaningful for well-being (i.e., "lower" organisms are often assumed to have lower propensity to feel pain or distress). Modern biology now views life as a tree, not a ladder. A perceived lower level of sentience is not a valid justification for model choice. Going Beyond Replacement requires matching the best model species to the research question, and adopting the same level of rigor and care for all species.

*We present the 3Rs in the order of Reduction, Refinement, and Replacement, rather than the original order proposed by Russell and Burch (Replacement, Reduction, and Refinement). This is not to minimize the importance of implementing Replacement; rather, moving Beyond3Rs acknowledges that developing innovative Replacement techniques or implementing Soft Replacement requires an understanding of modern Reduction and Refinement methods, so we introduce these concepts first as a foundation.