2024 national statistics on the use of animals in science released

The Home Office has released the annual statistics for scientific procedures on living animals in Great Britain for 2024. According to the data, a total of 2.64 million scientific procedures on living animals were completed, representing a 1.1% decrease compared to 2023, and marking the lowest number reported since 2001. This continues the gradual decline seen from 2022 onwards.

While this decline may reflect advances made in the 3Rs of replacement, reduction and refinement, it is important to note that changes from year to year can also result from a number of other factors, including shifting priorities in scientific and medical research, as well as changes in funding and investment.

Regulation of animal research in the UK

Animal research in the UK is strictly regulated by the Home Office according to the policy and operations of the Animals in Science Regulation Unit. All scientific procedures involving vertebrate animals (other than humans) and cephalopods must be scientifically justified and performed under licence. The use of animals must be recorded, together with an assessment of the severity levels, and published every year in accordance with the Animals (Scientific Procedures) Act 1986 amended 2012.

A procedure is defined as anything that causes pain, suffering, distress or lasting harm equivalent to, or greater than, the insertion of a hypodermic needle in accordance with good veterinary practice (for example a vaccination). It also includes procedures related to the creation and breeding of Genetically Altered (GA) animals; where animals whose genes have mutated or have been modified are bred, but not used themselves in experimental procedures. These include all genetic alterations, even if the genetic modification causes no harm, or the genetic mutation exists in natural populations.

Animals used in scientific research in 2024

Of the total procedures in 2024, 95% involved mice, fish, birds or rats. Specially protected species, which include non-human primates, horses, dogs and cats, accounted for 1% of all procedures. Specially protected species may only be used when no other species is suitable, and applications to work with these animals must undergo additional scrutiny.

Within experimental procedures, 57% involved mice, followed by 16% involving fish, 10% rats, 8% birds, 7% other species and only 1% specially protected species.

For procedures for the creation and breeding of GA animals, 87% involved mice, 13% fish and 0.43% rats and birds.

Purpose of scientific procedures in 2024

Of the total procedures carried out in 2024, 54% (1.43 million) were classified as experimental, while the remaining 46% (1.21 million) involved the generation or breeding of GA animals. The number of procedures is typically higher than the number of animals used, as some animals may be involved in more than one procedure (re-used) under specific conditions.

Experimental procedures were carried out for a range of scientific purposes. Around 732,000 of experimental procedures (52%) were for basic research (the same proportion as in 2023), most commonly focusing on the nervous system, the immune system, and oncology.

Approximately 24% of procedures were for applied research, similar to 2023’s figure of 25%. Applied research aims to address the prevention of disease and the development of treatments, with the most common areas of research in 2024 being animal diseases and disorders (32%), human cancer (24%), and human nervous and mental disorders (14%).

The remaining 22% of experimental procedures were for regulatory purposes, (again similar to 2023). These include procedures for testing safety and efficacy of new drugs and treatments prior to human clinical trials, and the testing of products for veterinary use in animals.

Severity of procedures

All procedures must be licensed and assessed for severity, which is classified as sub-threshold, mild, moderate, severe, or non-recovery. Procedures are classed as “sub-threshold” when they do not cause suffering above the threshold (they cause less suffering than a needle injection). Mild severity is classed as very minor transitory pain, e.g. the equivalent having a blood sample taken. Moderate severity is greater than transient pain (for example surgery under general anaesthesia followed by pain relief during recovery). Severe suffering is when the procedure causes a major departure from an animal’s usual state of health or well-being. This may include long-term disease processes where normal activities such as feeding and drinking require assistance. Animals found dead, but where the level of pre-mortality suffering cannot be determined, are also are commonly classified as severe.

In 2024, approximately, 97% of experimental procedures were sub-threshold, mild, moderate or non-recovery (where the animals does not wake up after anaesthesia). The proportion of experimental procedures classed as severe remains the same as last year at 3%.

For breeding GA animals, 99% were sub-threshold, mild, moderate or non-recovery and only 1% were severe (the same as 2023). 1.05 million (87%) procedures used GA animals with a non-harmful phenotype.

Reaction from the RSB

Dr Doug Brown FRSB, Chief Executive of the Royal Society of Biology, commented: "Animal research continues to play a critical role in biomedical research, advancing our understanding of complex biological systems and disease mechanisms. Scientific research involving the regulated use of animals has been instrumental in progress across areas such as gene and vaccine therapies, cancer screening and treatment, and continues to provide vital insights into the physiological and genetic mechanisms underlying metabolic diseases, and neurodegenerative disorders such as Alzheimer’s.

Significant advances are being made to phase in non-animal alternatives, including organ-on-a-chip technologies, human cell-based approaches and the growing integration of computational and AI-based methods. These alternatives are used across an increasing number of applications, which hold promise to reduce our reliance on animal use within certain contexts.

We welcome the Government’s decision to publish a strategy aimed at accelerating the development, validation and uptake of alternatives to animal use, expected later this year. We hope this will support the ongoing efforts and progress made by the life sciences community. However, we recognise that animal research will remain necessary for the foreseeable future to develop medical treatments for both humans and animals, and to safeguard human, animal, and environmental health.

The UK life sciences community remains committed to achieving the scientific benefits of animal research while minimising harm. This commitment is upheld through adherence to the high standards of animal welfare and the application of the 3Rs principles: Replacement, Reduction, and Refinement.

The UK has a highly robust regulatory framework ensuring that scientists and laboratory staff are qualified and competent before conducting procedures on animals. Every research project is individually assessed and licensed by the regulator, and reviewed by local ethical committees.

The Royal Society of Biology supports the use of animals in research when no alternatives are available, and is committed to promoting openness and transparency in reporting the use of animals for scientific purposes.”

Professor Sarah Bailey, University of Bath and academic co-chair of the UK Bioscience Sector Coalition (UKBSC), convened by the RSB, commented: "Medical progress and the discovery of new medicines for both people and animals depends on the careful and ethical use of animals in research.

The annual statistics on scientific procedures shows the number of procedures involving animals has gone down.

The number of procedures using animals in the UK is now about 77% of what it was in 2019, before COVID.

The number of animals used in research depends on things like how much money is available for research, what kinds of research organisations are focusing on and developments with new non-animal methods that support or replace animal research.

In the UK, animal research is funded by the government through research councils (UKRI), as well as by charities and private companies. Because of the current economic challenges – higher costs and tighter budgets – there has been a reduction in research overall, which may explain the lower number of procedures in 2024.

Every year, the Home Office reports any “techniques of special interest”. This includes checking if animals were used to test ingredients for household products or alcohol and tobacco products. In 2024, there were no such tests.

A new addition this year is the forced swim test, which is now classed as a “technique of special interest”. In this test, an animal is placed in water, out of its depth with no means of escape.

In 2023, the Animals in Science Committee said that the forced swim test can help study antidepressants and stress-related behaviour. For mice, it usually means a 6-minute swim in a cylinder of water, after which they are dried, warmed and returned to their cage.

In 2024, there were 250 procedures involving mice in this test, all rated as either mild or moderate severity.

Non-animal research methods are improving all the time and, alongside animal research, are important in advancing UK bioscience. However, animals are still needed when there are no alternatives. Understanding complex biological systems, studying disease over the lifespan, and testing how new medicines work in the body requires the use of animals."