Why is animal research necessary?

Research using animals is essential for understanding the biology that underpins health and disease in both humans and other animals. Without such research, we would have few of the modern medicines, antibiotics, vaccines and surgical techniques that we take for granted in both human and veterinary medicine.

Animals are used to investigate fundamental biology, to model disease and to test potential new treatments before they are tested in humans. Animal research is only undertaken where there is no alternative.

What types of animal do you use at Cambridge?

The majority of the animals we use are mice and zebrafish – they make up 97% of all procedures at Cambridge. Where these species are not suitable, we use a small number of other animals, such as xenopus frogs, rats and sheep, as well as non-human primates, namely marmosets and macaques. 

What types of animal research do you carry out?

Some of the work carried out is fundamental research, aimed at understanding how humans and animals develop and how our immune systems and brains work, for example. This knowledge is essential for underpinning our understanding of health and disease for both medical and veterinary purposes. 

Other work is aimed at tackling specific diseases, for example in helping us understand how Parkinson’s disease affects the brain and motor system and how it might be tackled, or in developing new treatments for autoimmune diseases such as type 1 diabetes and multiple sclerosis.

How many procedures are undertaken on animals at the University of Cambridge each year?

The Home Office collects data on the number of procedures carried out, rather than the number of animals used. The following numbers of procedures based on Home Office Returns were carried out on animals for research at the University of Cambridge:


2018 2017 2016 2015
Mouse  107,140 134,118 133,456 151,101
Rat 3,202 3,511 3,523  3,567 
Zebra fish  30,589 18,747 17,431  24,768 
Other fish  0 0 85 145
Primate  53 39  52   59
Sheep  130 62 148  170 
Guinea pig  144 76 56 95
Other rodents 21 21 12 3
Rabbits 0 0 7 16
Chicken 30 48 0 218 
Other birds 0 0 5 7
Xenopus 659 1,353  619   931 
Total 141,968 157,975  155,394  181,080 

A ‘procedure’ is regulated and counts towards our Home Office Returns if it is carried out on a protected animal (such as those species listed above) for a scientific or educational purpose and may cause that animal a level of pain, suffering, distress or lasting harm equivalent to, or higher than, that caused by inserting a hypodermic needle according to good veterinary practice.

Procedures that are regulated include modifying the genes of a protected animal if this has the potential to cause the animal pain, suffering, distress or lasting harm; for example, breeding mice with harmful genetic defects is a regulated procedure if the intention is to keep the animals produced beyond two-thirds of the way through their gestation period. This helps explain why the numbers of mice and zebrafish are so high: each offspring born is counted as a procedure.

Why has the number of procedures in the UK increased year upon year?

Whilst every attempt is made to minimise the number of procedures undertaken in research, there has been an overall increase over the last decade due to the use of genetically-modified (GM) mice. If these breeding figures were to be excluded, the total number of procedures carried out year upon year would decrease slightly.

How severe were these procedures?

When applying to use animals for research purposes, researchers must assign a severity classification to the procedures they plan to undertake before authority to do the work is authorised by the Home Office.  Once their licence has been granted they must also record the actual level of suffering, i.e. severity experienced by each animal during the course of a procedure.

The prospective severity classification of a procedure is determined by the degree of pain, suffering, distress or lasting harm expected to be experienced by an individual animal during the course of the procedure.  After an experiment has been completed the researcher must record the actual level of suffering experienced by each animal.  The prospective severity classifications are defined by the EU Directive as Non-recovery, Mild, Moderate and Severe, examples of which are provided below.


Procedures, which are performed entirely under general anaesthesia from which the animal shall not recover consciousness.


Procedures on animals as a result of which the animals are likely to experience short term mild pain, suffering or distress, as well as procedures with no significant impairment of the wellbeing or general condition of the animals.

Mild procedures include:

  • anaesthesia
  • non-invasive imaging, like and MRI scan
  • short-term social isolation
  • taking a blood sample
  • superficial non-surgical procedures e.g. ear biopsies in mice and non-surgical implantation of recording devices and minipumps


Procedures on animals as a result of which the animals are likely to experience short term moderate pain, suffering or distress, or long-lasting mild pain, suffering or distress as well as procedures that are likely to cause moderate impairment of the wellbeing or general condition of the animals.

Moderate procedures include:

  • invasive surgery under general anaesthetic e.g. surgical implantation of a catheter into a blood vessel for long term drug delivery
  • causing cancer in an animal where the tumour growth impairs normal behaviour
  • feeding a modified diet which is deficient in an essential nutrient such that it affects the health of the animal
  • exposing the animal to something that they would normally run away from, without enabling them to run away
  • the breeding of genetically altered animals where the animals health is affected, e.g. genetic models of diabetes.


Procedures on animals as a result of which the animals are likely to experience severe pain, suffering or distress, or long-lasting moderate pain, suffering or distress as well as procedures, that are likely to cause severe impairment of the wellbeing or general condition of the animals.

  • any test where death is the end-point or where deaths are expected and it is not easy to determine when an animal is likely to die, e.g. models of aortic aneurysm
  • testing a device that could cause pain/death if it were to fail, e.g. testing devices designed to support patients at risk of heart disease
  • inescapable electric shock treatments, e.g. to induce a model of learned helplessness
  • breeding animals with genetic disorders that are expected to experience severe and persistent impairment of general condition, for example Huntington’s disease, and muscular dystrophy

Actual severity:
The above definitions and examples also provide a good insight into what animals could have experienced when undergoing procedures and so reflect how actual severity is determined.  The only difference is that in the UK the Home Office introduced a further actual severity classification known as sub-threshold.  This classification therefore appears when UK annual returns of procedures are published.


This is for procedures which were originally assigned an above-threshold pain or suffering classification, but when the work was undertaken the actual level of suffering was below that which would exceed the threshold at which procedures are licenced under the Act.

Sub-threshold procedures include:

  • breeding of genetically altered animals under project licence authority but without a harmful phenotype
  • dosing with a compound in feed where the animals ate normally and suffered no consequences of being dosed

Finally, any animals that are undergoing experimental procedures that are found dead and death could have been procedure related will be automatically classified as Severe unless the researcher can proved that the death was not procedure related.

Example procedures courtesy of Understanding Animal Research

  Sum of no. of procedures (2018) Sum of no. of procedures (2017)
Mice 107,140 134,118
Non-recovery 1,393 2,004
Mild 38,614 42,857
Moderate 15,677 18,179
Severe 1,675 2,451
Sub-threshold 49,781 68,627
Rats  3,202 3,511
Non-recovery 164 331
Mild 859 623
Moderate 1,868 2,172
Severe 64 43
Sub-threshold 247 342
Zebra fish 30,589 18,747
Mild 17,462 10,697
Moderate 2 144
Severe 2 12
Sub-threshold 13,123 7,894​
Primates 53 39
Mild 16 12
Moderate 37 27
Sheep 130 62
Non-recovery 5 0
Mild 4 4
Moderate 119 58
Sub-threshold 2 0
Guinea-Pigs 144 76
Non-recovery 0 6
Moderate 144 69
Severe 0 1
Other Rodents 21 21
Mild 21 21
Domestic Fowl 30 48
Mild 30 48
Xenopus 659 1,353
Mild 658 1,350
Moderate 1 1
Severe 0 2
Total 141,968 157,975

2017 Additional Data

Directive 2010/63/EU mandates that every five years (starting with data from 2017) every EU member state must submit details of the animals that are killed in research facilities without being used in any regulated procedure.

Additional data for 2017 (PDF)

How do you ensure high standards of animal welfare?

We believe that good science and good animal welfare go hand in hand.  The UK has the most rigorous animal welfare regulations in the world, and we consider adherence to these regulations as a minimum and will continue to aim for the highest possible standards of animal care.

We strongly agree with, and rigidly follow, the guiding principles emphasised by the Home Office on the need to refine protocols, keep the numbers of animals used to a minimum and replace the use of animals with other methods where possible. To this end, we encourage all staff involved in animal research and husbandry to continuously develop and improve on existing welfare standards, offering incentives to those that contribute, and rewarding those that are recognised by the laboratory animal welfare organisations.

Are you looking for alternatives to animal use?

We are committed to refining, reducing and replacing the use of animals in research - known as the 3Rs. Animals are only used where no alternatives are viable. Cambridge scientists are also leading research looking at finding viable alternatives. For example, in 2014, Dr Meritxell Huch from the Gurdon Institute won the UK’s international prize for the scientific and technological advance with the most potential to achieve the 3Rs for work to grow “mini-livers” from adult mouse stem cells.

Do you test cosmetics and household products on animals?

No. It is not permitted anywhere within the UK or the European Union to test cosmetics or household products on animals.