One of the first considerations in this case should be the proximate cause of the fracture in an animal that suffered a relatively minor mishap (drop of less than one foot). Did the osteoporosis research contribute to the fracture, or was the fracture an isolated accident? The case report suggests that the rabbit may have had 'poor bone density' as a result of the experimental procedures, which could have contributed to the fracture, but goes on to say that the fracture healed well with a simple cast, suggesting that poor bone density might not have been a critical factor. The potential for bone weakness and fracture should have been considered when the study was initially given to pain category C (no pain or distress) and should now be considered in a follow-up by the IACUC and in the annual report for these animals.

If the fracture was indeed related to the reduction in bone density induced by experimental conditions, a change in pain category may be appropriate for all treated animals (controls would continue to be category C). If the investigator determined that affected animals could be treated with analgesics, either within the study or after an animal was removed from the study, then pain category D would be appropriate for all treated animals. Considering this scenario and the appropriate use of anesthesia and analgesia, category D would be appropriate and category E, no analgesics, would not be considered. If the fracture was determined to have been an accident of husbandry and not related to experimental conditions, the animal would remain in category C, as originally classified for the study by the investigator and the IACUC.

The Animal Care Research Facility Inspection Guide1 provides examples that give guidance in this case. In example 1, “an animal that experiences unexpected pain due to the research procedure and has the pain recognized and appropriately treated would be placed in the D pain category”. In example 5, “an animal that experiences pain completely unrelated to the research procedure and has the pain recognized and appropriately treated would be reported in the pain category originally determined for the study”. Thus, both Margolis and Covelli were incorrect in their assumptions that the cause of the fracture did not determine the pain category for this animal.

The fact that the technician was allowed to adopt the rabbit after the fracture healed also gives us some information about the cause of this fracture. If the research procedures were associated with reduction in bone density sufficient to allow fracture of the tibia during a minor mishap, then the technician should not have been allowed to adopt the rabbit. Assuming that appropriate restrictions are in place for the adoption program at this institution, the research procedures must not have had sufficient effect on bone density to adversely affect the welfare of the rabbits. Thus, the original classification of pain category C for the study and the continued C classification for this particular rabbit would be appropriate.

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