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Cumulative severity

Combination of milder factors = cumulative severity

Animals used in research and testing can experience a number of potentially painful or distressing events (harms). These include transport, marking for identification, capture, handling, restraint, laboratory housing and husbandry, scientific procedures and the after effects of these, and humane killing.

It is well recognised that repeated stressors like these can affect overall severity, but it is not always easy to predict exactly how their effects interact and impact upon one another. The term ‘cumulative’ severity is often used, but harms do not ‘accumulate’, or simply add up. Animals may become sensitised to certain procedures, so suffering is increased, or they may habituate (become used) to them, which can reduce suffering. Allowing sufficient recovery time following stressful events such as transport or cage change before conducting a procedure can reduce cumulative effects, although the impact of some procedures (e.g. surgery without the most effective perioperative analgesia regime) may be long-lasting or permanent.

Two essentials for understanding and assessing cumulative severity are:

Cumulative severity cycle

These are closely linked and can be used to continually inform and update one another, as shown here.

The lifetime experiences of each animal should be carefully considered at the project planning stage, with input from people possessing a range of expertise including the researcher, the veterinarian and animal technologists. The AWERB or AWB may also be able to provide useful input. A major aim is to identify as many sources of suffering (harms) as possible, so that appropriate refinements can be researched and included in experimental protocols and within housing, husbandry and care, wherever this is compatible with the science. Another important aim when reviewing the animal’s lifetime experience is to identify and define humane endpoints.

The review of lifetime experiences at the project planning stage can also help to determine indicators of suffering that are tailored to the species, strain (if appropriate) and procedure and can be used to assess welfare day to day throughout the procedure. If there are good welfare assessment systems in place for recognising and assessing behavioural and physiological indicators of pain or distress, suffering can be acted upon sooner and more effectively - which will reduce severity. Standardised terminology with respect to welfare indicators can be useful in order to ensure that all staff are ‘on the same page’ (for example: and to avoid confusion that could delay intervention.

During and after procedures, records of ‘cageside’ observations can be reviewed to assess how accurately harms were predicted, how severely animals were affected (‘actual severity’) and how effective any refinements have been. All of this information, obtained using robust welfare assessment protocols, should then complete the circle and help to implement refinement in future projects. Assessing actual severity is essential in order to fulfil the legal requirement to report this to the regulator within the European Union.

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