Automated mouse euthanasia in an individually ventilated caging system: system development and assessment

We developed a CO2 euthanasia system that functions as an individually ventilated caging system and that accommodates the simultaneous euthanasia of as many as 70 cages of mice. The automated, logic-controlled system allows euthanasia of mice in their home cage, provides consistent and reproducible delivery of CO2, permits visualization of animals during euthanasia, and integrates various safety features. Requirements for the safe use of this system are that all cage locations are to be filled and that engineering controls (that is, a thimble connection) be used to minimize CO2 contamination of the immediate environment. The system was evaluated using mice that were nongravid and greater than 6 d of age. CO2 measurements were made over time to assess the reproducibility of intracage CO2 levels and the effect of 3 supply plenum pressures (0.35, 0.25, and 0.15 in. H2O) on maximal intracage CO2 concentration, CO2 fill slope, time until CO2 detection, and time until maximal CO2 concentration. Results indicate that both supply plenum pressure and cage position on the rack affect intracage CO2 concentrations. We also conducted behavioral assessments of mice undergoing euthanasia to evaluate distress during euthanasia at 2 plenum pressures (0.15 and 0.35 in. H2O). Personnel experienced with laboratory mice did not discern differences in mouse distress associated with either cage location or plenum pressure. This system was safe, effective, and labor-saving for euthanizing large numbers of mice in an aesthetically acceptable and humane manner compatible with recommendations provided in the ACLAM 2005 Report on Euthanasia.