Non-stun slaughter: An evidence-based case

Peter Phillip Smith looks into why the non-stun slaughter of animals – such as that practised with halal methods – is unnecessary and causes undue suffering.


The Welfare of Animals at the Time of Killing (England) Regulations 2015 prohibits animals from being slaughtered for food without prior stunning – defined as being rendered unconscious by a set of pre-defined methods which include use of a captive bolt pistol and electrical stunning.

Once an animal has been stunned, additional methods must be utilised in order to ensure the animal is culled before regaining consciousness. A common sequence of events when culling cattle is use of a penetrative captive bolt, which causes the animal to be rendered unconscious immediately.

The 15 second rule

The law then stipulates that the animal must have its blood vessels cut within 15 seconds of being stunned, thus resulting in the animal never regaining consciousness as a result of the loss of all its blood (exsanguination). As pain can only be experienced when an animal is conscious, this means a properly stunned and exsanguinated animal can never feel pain.

There is an exemption to the requirement of pre-stunning an animal before slaughter, which allows some abattoirs and slaughter men to exsanguinate animals without prior stunning for religious purposes. This exemption was also present in the 1995 legislation (Welfare of Animals (Slaughter or Killing) Regulations 1995 ) which the 2015 legislation superseded.

First legislation

The first legislation in the UK (and the world) protecting animals was published in 1822, and therefore we can at least say no legislation before then existed governing how animals should be culled. As to when the first legislation came into force stipulating how animals must be slaughtered is outside the scope of this document, but it is fair to say that animals have been slaughtered without pre-stunning for a very long time, and that this is not a recent phenomenon.

Given the new data and understandings we have about animal physiology and measures of suffering, however, it seems sensible to continually review the existing legislation and challenge where necessary. The introduction of the 1822 legislation is a prime example of this. The recent increases of meat in the food chain from non-stun slaughter methods has increased scrutiny of this area of animal welfare, another explanation as to why this is being reviewed with more frequency now than in the past.

Expert opinion 

The British Veterinary Association believe that slaughter without pre-stunning is unnecessary and causes unnecessary suffering at the time of slaughter. The Federation of Veterinarians of Europe (FVE), the Farm Animal Welfare Council (FAWC), the RSPCA and Humane Slaughter association also share this view.

Evidential basis

The available evidence supporting this expert consensus view largely concerns the pain experienced by cutting the skin (epithelium), muscle and nerve endings which run throughout the body of mammals. Cutting and damaging tissues, no matter how sharp the knife is, will undoubtedly cause a degree of pain.

Supporters of non-stun slaughter maintain that the immediate drop in blood pressure caused by severance of the major blood vessels renders the animals insensible to pain. When thinking mechanistically and from first principals, when compared to pre-stunning which is instantaneous, cutting the neck of an animal clearly cannot result in a quick and as consistent onset of unconsciousness.

This onset of unconsciousness as a result of cutting the major blood vessels is due to a drop in blood pressure to the brain – the time to unconsciousness in animals which have been culled without prior stunning has been investigated several times and published in peer reviewed literature. Evidence of pain and distress has also been presented in peer reviewed literature.

“Not conclusive” ?

The main counter-argument against this evidence is that it’s “not conclusive”. This line of argument itself is illogical as there can be no conclusive evidence of pain as one would have to put themselves into the mind of the animal which is impossible. Indeed, most of science, especially in the area of animal health and welfare, gather supporting evidence to make decisions.

The ASPA legislation which safeguards the welfare of animals used in scientific procedures, for example, uses measures of pain and consciousness which are not conclusive, but which are likely to reflect the true  welfare status of the animal because it’s impossible to know for 100% sure whether an animal is in pain. Indeed this is exactly the reason for requiring animals at slaughter to be stunned, making any exemptions counter-intuitive – either the animals are more likely to suffer without being stunned or they aren’t.


The fact that a significant proportion of animals (>50%) which are exsanguinated by a cervical incision without prior stunning take over 10 seconds to collapse is extremely strong evidence that they are still conscious – it’s inconceivable with no basis in science, to suggest they are unconscious but still standing.

EEG evidence, as well as the fundamental understanding about how nociception and pain perception occur in mammals, supports the fact that an incision to the overlying skin, muscles, nerves and connective tissues of the neck will illicit pain. The fact that we cannot be conclusive about this unless we find a way of putting ourselves into the consciousness of animals is a ludicrous argument, and would negate all animal welfare law in the UK on the basis of we can’t prove it 100%.

Stunning an animal renders it unconscious instantaneously, and therefore unable to experience pain and suffering. Given the scientific knowledge we now have surrounding non-stun slaughter, an exemption allowing it to continue to occur in 2017 can no longer be justified, especially in a country such as the UK which has historically led the way in animal health and welfare legislation and best practice.

Publications supporting the fact that non-stun slaughter causes unnecessary suffering 

(Gregory, Fielding et al. 2010) – 174 Cattle had their cervical blood vessels cut as part of non-stun slaughter and were observed. 14% of cattle collapsed, stood up again, before finally collapsing. The average time to collapse was 20 seconds. 8% of the animals took >60 seconds to collapse. It is assumed that a lack of collapse is consistent with consciousness and therefore ability to feel pain. Development of false aneurysms was statistically correlated with an increased time to collapse – (A false aneurysm is an inevitable complication of non-stun slaughter whereby the severed ends of the carotid arteries can form a structure which impeded or stops exsanguination).

(Gibson, Dadios et al. 2015) – 644 cattle had their cervical blood vessels cut as part of non-stun slaughter and were observed. This again showed false aneurysms detected ost slaughter were associated with a longer time to collapse. This study again showed average time to collapse was 18.9 seconds when a conventional non-stun slaughter method was used. Around 4% (26) animals took more than 60 seconds to collapse in this study, and the majority of animals took >10 seconds (Graph below).

(Gibson, Johnson et al. 2009) – 17 anaesthetised cattle had their brain activity measured (by EEG) as a result of either cutting the neck and associated blood vessels of merely cutting of the vessels but not most of the other neck tissues. The results of this showed that brain responses were measured after cutting the neck tissue but not due to a loss of blood flow alone. This gives further evidence that nociceptive signals (nerve signals which would likely result in pain being experienced if the animal was conscious and not anesthetised) result from cutting the neck tissues.


Gibson, T. J., N. Dadios and N. G. Gregory (2015). “Effect of neck cut position on time to collapse in halal slaughtered cattle without stunning.” Meat Sci 110: 310-314.

Gibson, T. J., C. B. Johnson, J. C. Murrell, J. P. Chambers, K. J. Stafford and D. J. Mellor (2009). “Components of electroencephalographic responses to slaughter in halothane – anaesthetised calves : effects of cutting neck tissues compared with major blood vessels.” N Z Vet J 57(2): 84-89.

Gregory, N. G., H. R. Fielding, M. von Wenzlawowicz and K. von Holleben (2010). “Time to collapse following slaughter without stunning in cattle.” Meat Sci 85(1): 66-69.

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