Procedures where 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 well-being or general condition of the animals are classified as ‘severe’. Examples include:

  • any test where death is the end-point or fatalities are expected
  • testing a device that could cause pain/death if it were to fail
  • inescapable electric shocks
  • 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


In 2016, 153,558 procedures (experimental and breeding) in Great Britain were reported as severe (3.9% of all procedures). 133,240 (86.8%) of these procedures were in mice, 9,859 (6.4%) were in fish, and 5,740 (3.7%) were in rats. The remaining 3.1% of severe procedure took place in other species including guinea-pigs, rabbits, dogs, ferrets, pigs, birds, primates, and amphibians.

Induction of liver failure in mice

Liver failure is an extremely serious condition and remains a major problem across the world. Alcohol, diet, and drugs are major influences of liver injury, and damage to the liver tissue can provoke the body’s immune system into a response. This response may exacerbate the injury, worsening liver problems. Patients with severe forms of liver damage also show defects in their immune system that make them particularly susceptible to contracting infections. Research is needed to help advance our understanding of how the immune system reacts to liver injury and how to prevent the rapid deterioration of the organ due to an excessive immune response. Despite great advances using liver disease patients and techniques that do not require live animals, the use of animal models is still essential to look at the complicated interactions between liver disease and the immune system. Therefore, mice models of acute liver injury are often used in this area of research.

Acute liver failure in mice can be induced in different ways. Mice may be fasted (with free access to water) to ensure that glutathione levels are depleted, and then administrated with Paracetamol via intraperitoneal or oral gavage. Another way consists of administrating mice with D-galactosamine (Gal) and LPS - the animals reach the acute stage of liver failure by 8-12 hours. During these procedures, anaesthesia and techniques to reduce harm are used wherever possible to minimising suffering.

Inducing Parkinson's disease in a marmoset (species of monkey)

"The marmoset is injected in the stomach with a substance called MPTP, which is known to cause symptoms like those of Parkinson's disease. After a series of injections, the marmoset becomes increasingly less able to move and experiences 'tremors' that are typical of Parkinson's. In the end he is unable to balance on a perch, loses body weight and has to be hand fed, given extra fluids and kept warm. He then slowly begins to recover and over several weeks regains movement until he is almost physically fit, although still with a slight tremor. The marmoset is then used to test the effectiveness of a potential drug for Parkinson's, which is given by injection into the stomach either once or several times."

Example taken from Openness in Animal Research Dialogue.

This video shows Geoff Butcher, a patient with Parkinson’s Disease,  interviewing a scientist who uses Marmosets as an animal model to  investigate Parkinson's disease. The scientist does this by using MPTP to destroy the substantia nigra in the Marmosets. This is the part of the brain that is associated with the fine control of movement. Damage to the substantia nigra that causes the symptoms of Parkinson's disease.

In 2016, 20 experimental procedures in primates were reported as severe.

Last edited: 19 February 2018 13:18