Assessing Rodent Euthanasia Methods through Evaluation of Physiological Parameters

Abstract

Two million rodents are euthanized in Canada annually; the majority of these animals will be euthanized with carbon dioxide gas. Avoidance-approach studies have indicated that its use is aversive for rodents. Other studies have linked CO2 nasal nociceptor activation (painful in humans) to bradycardia. This study assessed the following euthanasia methods through evaluation of physiological parameters (electroencephalography, electrocardiography, electromyography): carbon dioxide, isoflurane, carbon dioxide/oxygen and sodium pentobarbital. Loss of consciousness was assessed by testing the righting reflex. Thirty-two adult female Sprague-Dawley rats were instrumented with telemetric transmitters and euthanized seven days post-instrumentation. Carbon dioxide caused bradycardia in rats prior to loss of consciousness, the severity of bradycardia was lessened by the addition of supplemental oxygen. Carbon dioxide was the fastest euthanasia technique followed by isoflurane, carbon dioxide/oxygen and sodium pentobarbital. Neither recumbency nor muscle quiescence were reliable indicators of loss of consciousness. Overall isoflurane is the preferred method of euthanasia.