Interstrain Differences in CO2-Induced Pulmonary Hemorrhage in Mice

Area of Science:

• Veterinary Medicine
• Animal Welfare
• Toxicology

Background:

• Carbon dioxide (CO2) is a common euthanasia gas for rodents.
• Current guidelines recommend slow filling (SF) but discourage prefilled containers (PF).
• Pulmonary hemorrhage (PH) has been observed with SF euthanasia.

Purpose of the Study:

• To evaluate if air-displacement rate (SF vs. PF) influences pulmonary hemorrhage (PH) or nasal hemorrhage (NH).
• To compare PH and NH prevalence between SF, PF, and isoflurane overdose (IO) euthanasia methods.
• To assess the impact of mouse strain and age on euthanasia-induced hemorrhage.

Main Methods:

• BALB/c and C57BL/6 mice (6 wk and 6 mo) were euthanized using SF or PF CO2 methods.
• A subset of 6-mo-old male BALB/c mice underwent isoflurane overdose (IO) euthanasia.
• Gross and histologic evaluations of lungs, nasal turbinates, brain, and reproductive organs were performed and scored for hemorrhage.

Main Results:

• Hemorrhage severity was not affected by mouse age or sex.
• BALB/c mice exhibited more severe PH with SF compared to PF.
• Both SF and PF induced more severe PH in BALB/c mice than in C57BL/6 mice.
• SF euthanasia resulted in more severe PH in BALB/c mice than IO euthanasia.
• Nasal hemorrhage (NH) prevalence was not influenced by any euthanasia method.

Conclusions:

• Euthanasia method significantly impacts pulmonary hemorrhage development.
• The choice of euthanasia method should consider the specific mouse strain.
• SF CO2 euthanasia is associated with increased PH in BALB/c mice compared to PF or IO.