Definition and examples of the 3Rs

Reducing animal experiments and reducing the distress caused to animals – these are the objectives of the 3Rs strategy. It was proposed by the two scientists William Moy Stratton Russell and Rex Leonard, who, in the 1950s, were looking for ways to achieve these goals. In their book Principles of Humane Experimental Technique, they established the three guiding principles for responsible research involving animals. These principles are aimed at reducing the number of animal experiments as well as preventing, or at the least lessening, the suffering caused to laboratory animals.

Today, the 3Rs are an important component of Swiss and international legislation governing the use of animals in animal testing. The 3Rs stand for a strategy that is intended to reduce the number of animals used in experiments and to reduce animal experimentation overall; it also aims to mitigate the suffering and distress caused to the animals. At the same time, it improves the scientific quality and relevance of experiments.

Reduce: Reducing the number of animals used in the experiment

Statistical significance must be ensured with a sufficient number of animals. Reduce means e.g. the use of imaging procedures, with which animals can be examined without an invasive procedure, and with which data can be gathered multiple times with only a single animal. Examples include:

• Magnetic resonance imaging (MRI)
• Positron emission tomography (PET)
• Computer tomography (CT).

These imaging procedures for instance enable us to visualise pathological alterations of an organ and thus to study the effect of investigational substances or procedures. Animals can be examined repeatedly, rather than being euthanised every time an experiment is conducted. In addition, improved statistical methods and investigative procedures make it possible for fewer animals to be euthanised in experiments.

Refine: Lowering the level of distress caused to the animals by reducing pain and stress, thereby improving the significance of the experiments

Examples include:

• Designing test conditions that lower the level of distress for laboratory animals, e.g. by introducing new methods that reduce the stress on the animals, such as a gradual adaptation to the test conditions or a less stressful administration of drugs: allowing animals to consume drugs mixed with their feed, rather than applying them orally with a syringe. For example, pigs will eat drugs concealed in mango yoghurt voluntarily, hence without experiencing any stress. Conditioning animals for the intended procedure (e.g. by way of clicker training, an educational method).
• Making available improved, more attractive husbandry conditions (toys, tunnels for rodents).
• Refining methods, e.g. introducing new blood collection techniques that cause the animal less stress.

Replace: Replacing animal studies

Examples include:

• Using cell, tissue and organ cultures:

Analysing the biological activity in cell cultures rather than in live animals. However, not all questions can be answered in this fashion, as a biological organism is complex and many interactions and effects can be explored only in a complete system.

• Using organisms in developmental stages when, based on the current state of knowledge, they do not experience pain, suffering or stress (e.g. incubated chicken eggs in early stages, roe)
• Using microorganisms or animals with "lower sentience" (invertebrates, such as the nematode caenorhabditis elegans or insects, such as the fruit fly drosophila melanogaster)
• Using human tissue or cells, e.g. human blood

Pyrogen testing: Pyrogens are substances that are capable of inducing fever in human beings, such as bacterial residues known as endotoxins, or substances of non-biological origin, like rubber abrasion particles. New drugs therefore need to be tested for these substances. In the past, these tests were conducted with rabbits, by injecting them with the substance and then measuring their body temperature. The alternative methods used today are based on human blood cells.

• Using computer simulations: These require the prior use of animal experiments to collect data. Computer simulations must be based on information that allows reliable conclusions to be drawn for the live animal. This means that the simulations cannot be programmed without previous animal experimentation.
• Multi-organ chips: Products designed to simulate the interaction between two or more organs of a body are now available. The chips aim to simulate processes inside the body, but they are not capable of satisfactorily replicating the complete complex interaction of cells, organs, hormones and enzymes.
• Induced pluripotent stem cells.

Alternative methods are also increasingly being used to train people involved in animal experiments. In Switzerland, the training required for the conduct of animal experiments is stipulated by law. Rodents (mice and rats) and rabbits are used for this training, to practice the different forms of application. For several years now, an artificial ear has been used initially to practice drawing blood from a rabbit’s ear, before the blood is collected from a live animal. This helps reduce the stress on the rabbits.

Further, whenever possible, film clips or computer simulations are used for training purposes. For example, euthanasia is taught using film or computer animation that illustrates the cardiac function of a frog – rather than with the euthanasia and dissection of a live frog, which used to be common for biologists and veterinarians during their studies.

Alternative methods are limited

However, completely forgoing animal experimentation is not a viable option today, either for basic research or for the development of medicinal products. Tests involving cell, tissue and organ cultures are not capable of simulating the complex phenomena taking place within a body. Examples here include neurodegenerative disorders, such as Parkinson’s and Alzheimer’s disease, or mental illnesses, including schizophrenia and depression. Multiple sclerosis is a prominent example of a complex immunological disorder; the nerve cells in the central nervous system (brain and bone marrow) are attacked by the immune system, causing local inflammation and interference with different bodily functions, which may include visual disturbances and loss of balance.

When new medicinal products are developed, it should be noted that alternative methods must be approved as official test guidelines by the competent regulatory authority, Swissmedic in Switzerland. For this purpose, substitution and supplementary methods must demonstrate, on the basis of international validation studies, that their significance is adequate to replace existing, legally prescribed methods involving animal experiments.