A study of different euthanasia techniques in guinea pigs, rats, and mice. Animal response and postmortem findings

Abstract

Methods for euthanasia in laboratory animals should primarily be chosen with regard to animal welfare. safety of personnel and the purpose of the experiment, In the present study different killing techniques for guinea pigs, rats and mice were compared with regard to the animal response as well as post-mortem changes.
Stunning by a blow to the back ofthe neck (guinea pigs), decapitation with guillotine (rats) and cervical dislocation (mice) werejudged to be followed by immediate unconsciousness rapidly followed by a cessation of breathing. If possible, animals should be sedated or lightly anaesthetized before euthanasia using a physical method. Physical methods induced local traumatic damage (neck, brain. meninges) as well as changes in the respiratory organs, especially the lungs (emphysema,
bleeding. blood and fodder aspiration).
Intraperitoneal overdose of pentobarbital (ISO mg/kg bw) was followed by a calm induction within 2—3 minutes and a cessation of breathing within 8—1 1 minutes. with considerable individual variation Morphologically, acute degenerative lesions in myocardial muscle cells and circulatory changes in the kidney cortex as well as limited lung changes were demonstrated in all species. Pure carbon dioxide in an equilibrated system induced unconsciousness within 10—20 see in rats and mice and within 40 sec. in guinea pigs, followed by rapid death. Rats especially showed a moderate uneasiness during the induction. All species developed lung emphysema while myocardial cell changes and extravasation to alveoli were found in guinea pigs and rats.
Induction with (CO2/O2 (80:20) for 1 minute followed by pure CO; was judged to be the most humane method in all species from the animal welfare point of view. By adding oxygen the time for induction of unconsciousness was doubled in rats and mice but not much changed in guinea pigs. Breathmg ceased within 4 min in rats and mice and within 7 min in guinea pigs. In all specics this method induced lung oedema and considerable extravasation to ulveoli. This method cannot be  recommended for studies including morphological investigations ofltmgs.
From a strict animal welfare point of view the COQ/Oz-method is the most recommendable of the methods studied, followed by the pure CO2-method and next pentobarbital i/p. The equipment for inhalation euthanasia should be equilibrated With the actual gas or gas mixture before introduction ot'the animals. From the animal welfare point of view it is clear that the handling of the animals and technical efficiency of the person in charge are crucial factors for a good result. Ethically. all euthanasia techniques call for properly trained personnel and knowledge about post-mortem changes for an optimal scientific outcome.