A review of methods used to kill laboratory rodents: issues and opportunities

Abstract

Rodents are the most widely used species for scientific purposes. A critical pre-requisite of their use, based on utilitarian ethical reasoning, is the provision of a humane death when necessary for scientific or welfare grounds. Focussing on the welfare challenges presented by current methods, we critically evaluate the literature, consider emerging methodologies that may have potential for refinement and highlight knowledge gaps for future research. The evidence supports the conclusion that scientists and laboratory personnel should seek to avoid killing laboratory rodents by exposing them to carbon dioxide (CO2), unless exploiting its high-throughput advantage. We suggest that stakeholders and policymakers should advocate for the removal of CO2 from existing guidelines, instead making its use conditionally acceptable with justification for additional rationale for its application. With regards to physical methods such as cervical dislocation, decapitation and concussion, major welfare concerns are based on potential inaccuracy in application and their susceptibility to high failure rates. There is a need for independent quality-controlled training programmes to facilitate optimal success rates and the development of specialist tools to improve outcomes and reliability. Furthermore, we highlight questions surrounding the inconsistent inclusion criteria and acceptability of physical methods in international regulation and/or guidance, demonstrating a lack of cohesion across countries and lack of a comprehensive ‘gold standard’ methodology. We encourage better review of new data and championing of open access scientific resources to advocate for best practice and enable significant changes to policy and legislation to improve the welfare of laboratory rodents at killing.

The perspectives of UK personnel towards current killing practices for laboratory rodents

“…The most common agent used for overdose of anaesthesia for laboratory rodents is injectable pentobarbital 23,24 . Unlike companion animals, the placement of intravenous catheters is extremely difficult in laboratory rodents and therefore this approach involves intraperitoneal injection of barbiturate agents following restraint of the animal 14 . This has obvious welfare consequences including the stress associated with restraint, pain and discomfort upon introduction of the agent into the peritoneal cavity and increased risk of perforating the bowel 23,25,26 .…”

“…This method involves the separation of the cervical vertebrae resulting in lethal trauma to the spinal cord and is commonly performed by placing the finger (manual) or an instrument (mechanical) behind the base of the skull whilst pulling the tail firmly to achieve rapid separation of the high cervical vertebrae. This technique requires speed and accuracy (regarding dislocation location) to ensure method success 14,15,29 . Therefore, operator confidence is crucial for ensuring rapid separation of the cervical and not thoracic region of the spinal cord.…”

“…One argument for its continued use is that currently there is a lack of a more humane high throughput alternative available. Further, as highlighted in a recent review 14 the remaining permitted methodologies such as overdose of anaesthetic, cervical dislocation and blunt force trauma are understudied with regard to their ability to provide a humane death and therefore aren't without animal welfare concern due to their potential for inaccuracy and high failure rates 14,15 . Notwithstanding growing concern surrounding whether all methods listed in Schedule 1 are actually capable of inducing a humane death 4,5 , a lack of consistency in method application and choice across institutions could also result in unnecessary suffering during killing.…”

Paracrine Signals in Calcified Conditioned Media Elicited Differential Responses in Primary Aortic Vascular Smooth Muscle Cells and in Adventitial Fibroblasts

“…As stated previously, CO 2 asphyxiation, followed by cervical dislocation, were used to euthanize animals [ 78 , 79 ]. Body weight and non-fasting blood glucose measurements were taken at the time of euthanasia, followed by removal of the thoracic aorta ( Supplementary Table S1 ; ) [ 80 ].…”

"The Most Gentle of Lethal Methods": The Question of Retained Consciousness Following Decapitation

“…Thus, the maximum time that pain and distress may be perceived is 2.7 seconds [ 13 ]. Since then, this approximate measurement - sometimes increased to three to six seconds - remains the rule of thumb for estimating the time to LOC in decapitated rodents [ 14 , 15 ]. Most tellingly, in the 2000 Report of the AVMA Panel on Euthanasia, the Panel dismissed its earlier concern over decapitation and ruled that it was a humane method of euthanasia for rodent models [ 12 ].…”