Laboratory Rodents Deserve Better Than Improvised Killing Methods

Rodents make up the majority of mammals used in biomedical research, accounting for roughly 70% of all experimental procedures across the U.K., according to government statistics. When a study is complete, or when animals are surplus or no longer needed for breeding, they must be humanely killed. In the U.K., this is governed by Schedule 1 of the Animals (Scientific Procedures) Act (1986), which lists several approved killing methods for rodents. These include anesthetic overdose, carbon dioxide, concussion, and cervical dislocation.

Of these, prior research found that cervical dislocation is the preferred method for more than half (57.5%) of U.K. laboratory personnel. The technique involves separating the vertebrae at the top of the spine and can be performed either manually, using the thumb and forefinger, or with a mechanical aid. For rapid loss of consciousness and death to occur, the separation must happen as high on the spinal column as possible, ideally at the joint between the skull and the first vertebra. Despite its widespread use, no standardized technique exists, and no purpose-built, commercially validated tool for rodent cervical dislocation is currently on the market.

This study set out to document how cervical dislocation is actually performed across U.K. research institutions. Specifically, the researchers looked at what techniques and tools are most commonly used for mice and rats.

The team distributed an anonymous online survey through major U.K. animal care and welfare networks between August and December 2023. Questions covered the methods and tools used for cervical dislocation, participants’ views on which physical actions constitute a successful dislocation, the existence of institutional standard operating procedures (SOPs), and perceptions of how humane the method is.

A total of 317 participants completed the survey in full. Most came from academic institutions (83%), with slightly more identifying as researchers (49%) than technicians (39%). Experience levels ranged widely, from less than one year (3%) to more than 24 years (17%). Most participants primarily worked with mice (98%), though a substantial proportion also worked with rats (38%).

Different Standards For Mice And Rats

The survey found a striking divide between how mice and rats are killed. For mice, most respondents (69%) relied on manual techniques with no added equipment, while 26% used a mechanical aid. For rats, this pattern reversed: more than two-thirds (67.5%) used mechanical tools, with only 15% relying on manual methods.

The researchers note that this divide isn’t reflected in current U.K. legislation, which treats rodents as a single regulatory group. They suggest that weight-based rules, which require sedation or anesthesia for rodents over 150 grams before cervical dislocation is applied, may inadvertently be driving greater dependence on mechanical aids for rats, since adult rats routinely exceed that threshold.

Improvised Tools And No Consensus On Technique

The tools in use across U.K. labs were largely improvised — ordinary objects never designed for killing. For mice, the most commonly reported items included metal rods (27%), closed scissors (20%), and pens (16%). For rats, metal rods were most common (42%), followed by cage scrapers and closed scissors (both 18%), along with items as improvised as broom handles, rulers, and wrenches (2% each).

Alongside the diversity of tools, there was little agreement about which physical actions are needed for the technique to work. For mice, manual operators most often cited a strong downward or forward push on the neck region. Those using mechanical tools more often emphasized a downward push combined with pulling the animal’s tail horizontally. For rats, the pattern among manual operators was notably different. The criteria most commonly cited were a lateral twist or a stretch of the neck region after separation. Those using mechanical tools again prioritized a forceful downward push.

By contrast, research on the cervical dislocation of chickens, where the method has received significantly more scientific attention, indicates that effective dislocation requires both a rapid stretch and twist applied together. Using only one of these components results in less complete separation, a slower loss of consciousness, and greater suffering. The survey found no clear consensus on these fundamentals among laboratory personnel, suggesting that practice is guided more by institutional habit and personal preference than by scientific evidence.

Institutional SOPs were also inconsistently in place. For mice, more than one in five respondents (22%) didn’t know whether their institution had a formal procedure at all. For rats, more than a quarter (27.5%) reported that no SOP existed.

When asked about humaneness, the vast majority of respondents (94%) considered cervical dislocation a humane method for killing mice, though those using manual techniques were significantly more likely to hold this view than those using mechanical aids. Perceptions for rats were less certain: among those who worked with rats, about two-thirds (66%) considered the method humane, while just under a third (29%) expressed some degree of disagreement.

Limitations

Because this was a self-report survey, the study captures participants’ beliefs about their practices rather than direct observations of what actually happens. Some respondents may have answered the questions about rats without routinely performing the procedure on them. And because responses were anonymous, the representativeness of the sample across the full U.K. research sector can’t be confirmed. That said, 317 completed responses from participants across diverse roles and institutions provide a meaningful picture of sector-wide practice.

Laboratory Rodents Deserve Better

This is the first study to document in detail how cervical dislocation is applied to rodents across U.K. research institutions, and the picture it reveals is troubling. Mice and rats are routinely killed using improvised, unvalidated objects, with techniques that differ widely and lack any empirical grounding. Institutional SOPs are incomplete or absent in a significant proportion of facilities. For advocates focused on the welfare of animals in laboratories, this research provides evidence that a method regulated as “humane” isn’t being applied in ways that reliably minimize suffering.

These findings support calls for stronger regulatory oversight of killing methods, development and use of validated tools, standardized training, and transparent auditing of institutional SOPs. Advocates can draw on this research to challenge claims that current killing practices adequately protect rodents in labs, and to push for meaningful reform. More fundamentally, though, a study documenting such widespread inconsistency in even the most basic welfare protection raises hard questions about whether the institutions and regulations governing animal research are able to live up to their stated commitments.

This summary was drafted by a large language model (LLM) and closely edited by our Research Library Manager for clarity and accuracy. As per our AI policy, Faunalytics only uses LLMs to summarize very long reports (~50+ pages) that are not appropriate to assign to volunteers, studies that contain graphic descriptions of animal cruelty or animal industries, and research on niche topics. We remain committed to bringing you reliable data, which is why any AI-generated work will always be reviewed by a human.