Skip to main content

On tissue collection from mice and rats

Current research projects at Karolinska Institutet (KI) involving tissue collection from mice and rats have come under scrutiny by Animal Rights Sweden and other organisations, and many people have contacted KI in protest.

We understand the reactions to using mice and rats in medical research, but animal studies are only done when there is no other alternative.

The purpose of medical research is to improve human health and to find treatments and drugs for diseases that cause suffering to many people. Animal experimentation is not conducted for fun - it is an expensive and complex practice, and would be rejected by scientists in favour of test-tube research if it were possible.

The projects in question at KI are designed to identify the genes that either contribute to the development of certain diseases or protect against them. As part of their work, the researchers clip the extremities of the toes of rats and mice to provide tissue samples for genotyping. The samples are taken at an early stage of development - often when the animals are only a few days old - before the toe bones have grown. It is not a case of clipping off entire toes.

This method of tissue collection is standard in Sweden and around the world, and is used because it is considered best for the animal and for the purposes of research. The samples are taken when the animals are young, since doing so causes the least distress to the animals and enables the scientists to identify the strains with the right genes so that they can avoid breeding ones with the wrong genes. This helps to minimise the number of animals used in an experiment, which scientists always endeavour to do. An advantage of toe-clipping is that it also serves to mark the animals used, and thus necessitates only one operation instead of two.

The method of taking tissue samples in this way has been evaluated many times*, and is recommended by European organisations for laboratory animal science as causing the least suffering to the animals. The main alternative methods of extracting the same amount of DNA are tail-clipping and, when the animals are much older, ear-clipping. None of the other methods have been shown to cause less distress to the animals.

Tissue collection using toe-clipping produces a very brief pain reaction of the kind observed on giving an injection (e.g. a sedative), and the animals quickly return to normal behaviour. Anaesthetics are not used since the researchers feel that this extra step in the process could disturb the animal more than just the tissue collection alone.

All animal experiments in Sweden must first be approved by an ethical committee on animal experiments, which weighs the benefits of the study against the potential suffering of the animals. These committees are independent, quasi-court authorities organised by the Swedish Board of Agriculture. A permit to take tissue samples was granted by one such ethical committee.

Using animals in research for the benefit of mankind is an issue that is subject to constant debate, as it should be. Researchers, animal handlers and vets at Karolinska Institutet are aware that animal experimentation can cause suffering, and the option of finding alternative methods is always considered. The procedures for testing and marking are being constantly refined and we are convinced that tissue samples will eventually become minimal (individual cells).

For more information, please contact the Communications and Public Relations Office


Report of the Federation of European Laboratory Animal Science Associations Working Group on animal identification.
Dahlborn K, Bugnon P, Nevalainen T, Raspa M, Verbost P, Spangenberg E
Lab. Anim. 2013 Jan;47(1):2-11