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FAQ about research with animals

On this page, we address the most frequently asked questions about research involving laboratory animals.

What is a laboratory animal?

A laboratory animal is an animal bred and/or used for experiments. This category also includes bred animals that ultimately are not used in experiments.

In the Netherlands, four types of laboratory animals are distinguished. In 2019, the distribution was as follows:

  1. Ordinary vertebrate animals, specially bred (70.9%)
  2. Genetically modified animals (19%)
  3. Animals living in the wild and studied in their natural environment (8.7%)
  4. Animals living in the wild but studied in the laboratory (1.4%)

What is an animal experiment?

An animal experiment encompasses all actions involving an animal in the context of an experiment or training where the animals experience discomfort. Discomfort is the legal term for the degree of distress animals undergo during an experiment. This includes pain, stress, loneliness, fear, and illness.

Why are animal experiments necessary?

We conduct animal experiments to gain more knowledge about the health of humans and animals. They help us answer scientific questions about:

  • The functioning and development of the body
  • The behaviour of animals and humans
  • The development of diseases
  • The functioning, dosage, and safety of medications

Laboratory animals are only used when there is no other way to obtain this information.

For what purposes does Leiden University use laboratory animals?

At Leiden University, we use laboratory animals to answer scientific questions in the fields of biomedical and biological research. There are two central research lines where we employ laboratory animals:

Read more about research involving laboratory animals under the Research with Laboratory Animals tab.

How does Leiden University ensure that animal experiments are conducted as animal-friendly as possible?

At Leiden University, animal caretakers and researchers with specialized knowledge of laboratory animals work diligently to care for the animals every day, closely monitoring their well-being. The animals are housed according to specific guidelines. Where possible, investments are made in providing more space, such as large aviaries for zebra finches to fly and cages where mice and rats have ample space for their nests.

Animals involved in experiments are subject to even stricter monitoring. Agreements, for example, are in place regarding the maximum level of discomfort. This ensures that animals do not suffer more than necessary. If an animal falls ill, a veterinarian is available to examine the animal and provide advice on treatments.

Read more about how we take care of our animals responsibly: Responsible research with animals.

How is it determined which animal is needed for a particular study?

The selection of the most suitable animal to answer a scientific question is based on what best mimics the situation under investigation. This may involve choosing a zebrafish or a mouse, depending on the experiment and the specific characteristics required. Importantly, the chosen animal should closely represent the conditions being studied, such as a human disease or a situation in the wild.

When is it permissible to conduct an animal experiment?

Animal experiments are not undertaken lightly; there are stringent regulations in place. Leiden University holds a license for conducting animal experiments. Additionally, the scientist must obtain a personal certificate to design an animal experiment. The experiment is part of a specific project license, which is applied for from the licensing authority: the Central Committee on Animal Testing (CCD).

All technicians and researchers involved in animal procedures must undergo training, and their competences must be verified by an education and training staff member. The experiment can only begin when it is fully outlined and approved by the Animal Welfare Body Leiden (AWB Leiden). The process of applying for an animal experiment typically takes around four weeks.

Can everyone work with laboratory animals?

No, not everyone is permitted to work with laboratory animals. This is regulated by the Animals Experiments Act. There are essentially three levels for working with laboratory animals.

  1. For the care of laboratory animals, there is the MBO (Intermediate Vocational Education) programme in Animal Care.
  2. Additionally, there is the bachelor’s degree in Laboratory Research, with a specialisation in laboratory animal science. These individuals specialise in performing complex procedures with animals, such as surgeries and injections.
  3. After obtaining a specific master's degree with a focus on physiology and anatomy, you can take the Laboratory Animal Science course, where you learn to design experiments. Upon completion, you receive the Article 9 certificate. With the master's degree and this certificate, you can apply for a project license for animal experiments.

Explore the Education and Training section for more information on education and training for working with laboratory animals.

Are there alternatives to animal experiments?

There are various alternatives to animal experiments; here are some examples:

  • In vitro tests: These are tests conducted outside the body, in test tubes or petri dishes, using cells, tissues, or organs from animals or humans. In the Netherlands, killing animals for organs is considered an animal experiment, so some in vitro experiments still fall under this category.
  • In silico modeling: This involves using computer simulations and mathematical models to predict interactions between chemicals and biological systems. Leiden has extensive expertise in this area.

For example, read about Professor Gerard van Westen's research: ‘Our model predicts what candidate drugs do in your body.’ Or about the research of pharmacologists professor Liesbeth Lange and postdoc Frédérique Kok: Mathematical model predicts drug concentration in the brain.

  • Use of human volunteers or cultured human cells

Micro-dosing is an example where healthy volunteers are administered very small amounts of new drugs to determine their effects.

Professor Christine Mummery's group at LUMC uses human stem cells to mimic organs and diseases for testing potential treatments.

  • Epidemiological studies: These studies use data from large groups of people to assess the effects of exposure to substances.
  • Reuse of existing data: This involves using data from previous studies to gain new insights.
  • Organ-on-a-chip technology: This utilises microengineering and biotechnology to develop advanced microsystems that mimic human organs.

For instance, Alireza Mashaghi's group conducts research on bioprinting human tissues to test drugs.

What does TPI stand for?

The Netherlands wants to be a global leader in innovations that render animal experiments unnecessary. Therefore, the Dutch government encourages the development and application of methods for research without laboratory animals through the Transition to Animal-Free Innovation (TPI) programme. Read more about alternatives on the TPI website.

How does Leiden University promote the use of alternatives?

The Leiden Animal Welfare Body (AWB Leiden) discusses whether research questions can be answered without laboratory animals before the start of each project. They actively communicate alternatives or bring together individuals with similar inquiries to explore alternatives collaboratively. Additionally, there are experiments involving animals where the animals do not experience pain or distress. In behavioural biology, this is an alternative that is frequently employed. Researchers observe animals in their natural environment or design experiments where animals engage in activities without pain or stress. For example, they might observe how fish voluntarily explore a new environment.

Do I have to use laboratory animals during my studies as a student?

No, at Leiden University, you can pursue all programs without using animals. However, if you engage in an internship that involves the use of laboratory animals, as a student, you will first receive education about working with them. This is important to ensure that you not only learn how to handle animals practically but also do so in a responsible manner.

Are laboratory animals used for educational and training purposes?

In principle, laboratory animals are not used during our bachelor's and master's programmes. However, they are used in training sessions for students and staff who may encounter laboratory animals during internships, research, or work. Proper training is essential for anyone working with laboratory animals. For training, we preferably use animals that are born in our own breeding programmes and were not used for experiments (breeding surplus). This way, these animals can be put to useful training purposes without the need for breeding additional animals.

Which types of laboratory animals are used at Leiden University?

The primary species used at Leiden University are fish and mice. Additionally, rats, birds, and cephalopods (such as squids) are also used.

See the page Facts & figures.

How many animals are used at Leiden University?

The number and types of animals used depend on the research questions being addressed at a given time. Therefore, an average figure may not be very meaningful for Leiden University. The numbers vary significantly each year. Under the Facts & Figures tab, you can find information about the number and types of animals used for research in the past few years.

Where do laboratory animals come from?

Most of the animals used are specifically bred for this purpose. Some laboratories breed the animals themselves, while others purchase them from specialised breeding companies or obtain them from fellow researchers. In some cases at Leiden, non-specially bred animals, that are caught in the wild, may be used. This is only allowed when conducting specific research on wild animals, for example, studying the migration behaviour of fish.

When is an experiment considered a laboratory animal experiment?

An experiment is considered a laboratory animal experiment when there is a scientific question (for research or education) answered with the help of an animal. The animal experiences discomfort equivalent to or greater than that caused by inserting a needle. Animals used in animal experiments are protected by animal experimentation laws. This applies to all vertebrate animals from a certain life stage, as specified in the law.

What happens during an animal experiment?

That depends on the research question. It can range from an injection or surgery to participating in a behavioural test. Most laboratory animals are euthanised at the end of an experiment.

Read also the stories about the research we conduct with laboratory animals.

What is the culture of care?

The culture of care is an environment in which we collectively take responsibility for the best possible care and treatment of our laboratory animals. We strive to care for all animals used in a laboratory experiment as well as possible and aim to minimise any discomfort they may experience. Within this culture, there is room for all colleagues to discuss their work, express concerns, and continually contemplate how we can further improve our research involving animals. More information can be found on the page: Responsible research with animals.

What happens to an animal after an experiment?

Most animals are euthanised after an experiment. This depends on the researcher’s question and the specific needs of the experiment. If organs are required, the animal often cannot remain alive. This is different if, for example, only blood is needed. In such cases, the animals are not euthanised and are reused in another study or, in rare cases, may be considered for adoption.

Deceased animals can often still be used for educational purposes. Students use them, for instance, to study anatomy.

Is it possible to adopt a (former) laboratory animal?

In some cases, our animals are available for adoption because they are no longer needed after an experiment or for use in a subsequent experiment. In Leiden, this opportunity may apply to zebra finches. However, most rodents and fish are genetically modified and cannot be adopted. When animals are adopted, they are examined by the veterinarian, and we ensure that the new owner has sufficient knowledge and attention to care for these former laboratory animals properly.

For inquiries about adopting laboratory animals, you can contact AWB Leiden.

What is a breeding surplus?

A breeding surplus includes all animals that were bred for scientific purposes but ultimately were not used in a laboratory experiment. Not all bred animals are suitable for research, for example, because they may lack the necessary genetic characteristics or have the wrong gender to address the research question.

How large is the breeding surplus at Leiden University?

This varies each year. You can find this information on the page Facts & figures.

What happens to the breeding surplus at Leiden University?

A portion of the breeding surplus is used for education and training. The remaining animals are euthanised. Many of our animals are genetically modified, for example, to simulate a specific disease. Consequently, reintroduction into nature or adoption is not possible.

What does genetically modified mean?

In genetic modification, the characteristics of a plant, animal, or micro-organism are altered. This can be achieved, for instance, by inserting a piece of DNA from one organism into another. Animals that undergo this process are referred to as genetically modified organisms (GMOs).

What is a donor animal?

To answer a scientific question, it is sometimes necessary to transfer an organ or cells from one animal to another. Donor animals are animals that are euthanised so that we can use their cells in other animals. We investigate whether this can influence the course of the disease. For example, consider bone marrow transplants in research on the immune system. In the Netherlands, euthanising a donor animal is considered an animal experiment. In the rest of Europe, killing animals for cells or organs is not classified as an animal experiment.


Still have a question?

Would you like to learn more about animal experiments or laboratory animals? Please, contact the Animal Welfare Body Leiden.

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