Severe procedures
Some scientific procedures or 'models' are more likely to cause severe pain, distress, or feelings such as sickness in animals.
Cumulative severity
An animal's lifetime experiences—including transport, handling, restraint, housing, etc.—may affect their ability to cope with scientific procedures. It is important to consider how the effects of all these events may interact with one another.
Mortality
For animal welfare, ethical and also often scientific reasons, mortality of animals should be avoided.
