Levels of Noxiousness
To help with this process various invasiveness, severity or Noxiousness Scales have been developed world-wide.
These help animal-based scientists work out what the negative impact of a proposed procedure is likely to be on the animals. While no such formal criteria exist in Australia, Animal Ethics Committees usually classify animal experiments in a similar manner.
Note that the higher the noxiousness of a procedure, the greater the anticipated benefits must be before it can be approved.
Procedures which do not cause anxiety, fear, pain or distress such as non-invasive observation of animals in unchallenging circumstances.
For instance: field observations of grazing behaviour on farms, or benign handling of tamed and trained animals which are familiar with all personnel and procedures and with the place where the procedures are conducted. Nutrition and growth studies where production is measured in response to benign dietary changes.
No suffering or noxiousness. Procedures where no justification is usually required.
Procedures which cause minor discomfort or low-level anxiety or apprehension for short periods.
For instance: experiments on completely anaesthetised animals which do not regain consciousness; standard methods of euthanasia that rapidly induce unconsciousness (e.g. anaesthetic overdose); taking a blood sample from a superficial vein; injecting a non-toxic substance; skin tests which cause low-level irritation without ulceration; feeding trained animals by a tube passed via the mouth into the stomach; movement of free-range domesticated animals to unfamiliar housing.
Little suffering or noxiousness. Procedures require justification.
Procedures which cause moderate anxiety, fear, pain, or distress for short periods or minor discomfort or distress for long periods.
For instance: recovery from major surgeries like opening and closing the rib-cage, bone operations, or removal of the uterus or gall bladder, done under general anaesthetic and with effective use of pain killers after the operation; surgical procedures on conscious animals but with the use of local anaesthetics to prevent pain during the operation and other pain killers after it; movement of excitable free-range domesticated livestock to unfamiliar housing.
Moderate suffering or noxiousness. Procedures require good justification.
Procedures which cause marked anxiety, fear, pain or distress where any suffering caused is ended by euthanasia or by therapeutic or other interventions before it becomes excessive or where the suffering is short-lived and complete recovery can occur. Experiments which cause moderate anxiety, fear, pain or distress for long periods.
For instance: recovery from major surgery done under general anaesthetic but without the use of pain killer after the operation (e.g. reference animals used in studies to test how well particular pain killers work after surgery done under anaesthetic); marked social or environmental deprivation; capture, handling, restraint or housing, without the use of tranquillisers, of wild or semi-domesticated animals that exhibit marked flight responses.
Severe suffering or noxiousness. Procedures require strong justification.
Procedures which cause severe, inescapable or unrelieved anxiety, fear, pain or distress where the intensity or duration, or both, of the induced suffering are at or beyond the limits of reasonable endurance.
For instance: conducting major surgeries without the use of anaesthesia (e.g. where the animal is immobilised physically or with muscle relaxants); testing the effectiveness of pain-killers (analgesics) in animals with induced severe pain.
Very severe suffering or noxiousness. Procedures require the most exceptional justification.