Grade O
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 usually require no justification.