Severity scale for ALS studies on transgenic mice with a mutant SOD1 gene
Severity | Description | Welfare issues during this stage |
Level 1 | Animals euthanised prior to disease onset, which is characterised by progressive weight loss or hind limb tremors. | No overt motor dysfunction. Phenotype is subclinical. Loss of motor function can be detected using rotarod or running wheels, but does not interfere with normal behaviour. |
Level 2 | Studies terminated at an early stage of disease: animals present trembling and weakness in hind limbs (by approximately 75 days) and mild body weight loss. | Minor. Loss of motor function can be detected using rotarod or running wheels, but has little interference with normal behaviour. |
Level 3 | Experiments terminated when animals are no longer able to reach food hopper or bottle spout. This occurs when animals reach a moderate (gait abnormalities and weakness) to severe (hind limb paralysis) stage of motor impairment (usually at 120–125 days). | Medium. Loss of motor function and body weight can be detected by monitoring (eg, by a clinical score sheet) and by checking self-righting ability. Refinement measures to address these welfare issues include provision of softer bedding material (eg, sawdust), elongated bottle spouts and mashed food on the cage floor. |
Level 4 | Animals euthanised after losing the ability to right themselves within 10–30 s after being laid on either side (one or both) or when percentage of weight loss reaches 15%–20% of peak body weight (usually at 130–140 days). | Major. Animals show severe locomotor impairment. Refinement as described for level 3. |
Level 5 | Animals are euthanised when reaching a moribund stage (complete paralysis) or allowed to die spontaneously. | Severe. At this stage, animals are unable to move, eat or drink. Animals which are not euthanised will die as a result of respiratory failure. |
Each severity level exemplified from the most commonly used B6.Cg-TgN-(SOD1G93A) G1H mouse. Classification was based on the most severe endpoint used in each publication.
ALS, amyotrophic lateral sclerosis; SOD1, superoxide dismutase 1.