The Federal Food Safety and Veterinary Office FSVO defines the severity levels of animal experiments. The greater the stress, the greater the degree of severity: according to the Ordinance on Animal Experiments (Art. 24), stress on animals caused by interventions or measures during animal experiments is divided into four stress categories. In the end, the burden on the animals must be weighed up against the benefit to justify the experiment. The expected benefit of animal experiments for society must be shown to be greater than the constraint, the suffering and the violation of the animal’s dignity.
Degree of severity 0: No constraint, e.g. observational studies:
“Interventions and handling of animals for experimental purposes which do not subject the animals to any pain, suffering or injury, do not cause them to suffer fear and do not impair their general state of health". (Definition FSVO)
This may involve, for example, feed studies in which the acceptance and tolerance of a special feed is tested or in which positive influences on the milk yield of cows are examined. The use of green fodder grown in Switzerland as a substitute for imported soya can also be tested in dairy cows – an experimental approach that benefits not only the cows but also the environment.
Severity 0 also includes behavioural observation studies in which new improved husbandry systems for livestock are tested or in which fundamental behavioural biology questions are investigated in a specific animal species. A test of new types of milking robots to see whether dairy cows can be milked more often and have better udder health if they can be milked at times they prefer is also a stress-free animal experiment.
Almost half of the experimental animals are used in severity 0 animal experiments, in which the animals are not stressed at all.
Degree of severity 1: slight constraint:
“Interventions and handling of animals for experimental purposes which cause slight pain or injury or slight impairment of their general state of health.”
This includes measures that can only be performed on an animal under anaesthesia, e.g. applications that are technically difficult to perform or imaging images using MRI or computer tomography, during which the animals are not allowed to move. Feeding a high-fat diet for experimental purposes, which causes mice to become fat without developing diabetes mellitus, is also considered a mild exposure. Another example is infections for experimental purposes that do not cause any clinical symptoms in the experimental animals, or at most only weak ones in the short term. Such infections are carried out, for example, to study the course of parasitic diseases in animals (intestinal and liver worms) and humans (malaria).
Degree of severity 2: moderate constraint:
“Interventions and handling of animals for experimental purposes which cause short-term moderate or medium- to long-term slight pain, suffering or injury, short-term moderate fear or short to medium-term severe impairment of their general state of health.”
As an example, tolerance studies can be given with administered substances that are expected to cause short-term moderate or long-term mild reactions without higher mortality and that do not cause severe distress to the animals. Surgical procedures such as castration of females or placement of implants on the intact musculoskeletal system also fall under this severity level.
Degree of severity 3: severe constraint:
“Interventions and handling of animals for experimental purposes which cause medium to long-term moderate pain or severe pain, long-term moderate to severe suffering, medium- to long-term moderate injury or severe injury, long-term severe fear or severe impairment of their general state of health.”
This includes, for example, the transplantation of aggressive tumours into animals to study tumour development or joint or organ transplants.
are decisive for limiting the degree of severity: The researchers must specify precisely the levels of constraint or results which require an animal experiment to be aborted and when palliative measures such as the use of painkillers must be applied.