The science of slaughter: Is the stunning of pigs in UK slaughterhouses currently humane?

6 May 2022

First published in Alfred Journal: https://www.winchester.ac.uk/about-us/academic-excellence/learning-and-teaching-development/alfred-journal/

Introduction

The UK public are given assurances that animal welfare at slaughter in the UK is high, in part because animals are stunned prior to slaughter. Conversations around slaughter are often focused on ethics; the philosophical rights and wrongs of killing or around a vegan agenda. However, what about the science of slaughter? What does the evidence looking at the practicalities and measurable welfare factors tell us about stunning?

This essay examines both the scientific evidence and welfare concerns that surround the methods of stunning used commercially in the UK today. Significantly, many stakeholders repeatedly state that more humane commercial methods need to be found. It is not only animal organisations, with an agenda, that take issue with stunning method issues, but researchers, experts and government bodies also. The ongoing topical debate is important given the welfare implications, high number of pigs effected and lack of awareness by the public. This essay first introduces stunning, then examines electrical stunning, CO2 stunning, compares the two and finally acknowledges the significant number of stakeholders raising concern and concludes that, scientifically, we do not have humane stunning of pigs in the UK. There are numerous other important concerns outside the scope of this essay, including the serious documented issue of violence towards animals at slaughter in the UK, as well as transport, lairage conditions, handling and movement of animals.

Pigs at the slaughter house                                                                

Inducing unconsciousness, termed ‘stunning’, before slaughter is done in the pursuit of avoiding death related suffering. In the UK over 10 million pigs are killed each year, after either electrocution or CO2 (carbon dioxide) stunning.

Pigs are highly social and intelligent animals (RSPCA, n.d). In the UK 10,751,000 pigs were slaughtered in 2018 (DEFRA, 2018a). In October 2020 alone 981,000 pigs were slaughtered (DEFRA, 2020). Humane slaughter can be defined as stunning and slaughter that is ‘instant or non-aversive’ (Lymbery, 2018 [online]). Legislation in the UK requires animals to be stunned prior to slaughter so the animals are unconscious during sticking (cutting the neck to severe the major blood vessels) and bleeding, with the only exemption being for religious slaughter (Welfare of Animals at the Time of Killing (England) Regulations 2015). Stunning methods used are CO2 (86% of pigs), electrocution (around 14%), and mechanical which is rarely used (DEFRA, 2018b).

The inherent welfare issues relating to stunning itself, including pain and distress, have been of concern for decades. Researches in laboratory settings have attempted to find alternative methods to improve welfare at slaughter. To render large mammals instantaneously unconscious without welfare compromise is not a simple task. Moreover, the welfare of the animal is not the only concern in designing and implementing a stunning technique. The method needs to be financially viable for the industry, not compromise meat quality and must be able to be incorporated in the fast paced commercial slaughterhouse, many of which have high throughput rates, defined as 800 pigs per hour by the Humane Slaughter Association (HSA) (HSA, 2019:1). Errors in stunning, resulting in animals being conscious when cut, cause immense suffering. Both stunning methods are now explored.

Electrical

Until recently electrical stunning was the predominant method used to stun pigs. Government data shows around 48% were stunned electrically in 2013 (FSA, 2013) which fell further to around 14% by 2018 (DEFRA, 2018b). Despite this decrease in proportion there was a significant number, over 1.5 million, of pigs stunned using electrocution in 2018 (DEFRA, 2018a). In electrical stunning electrodes are placed spanning the animal’s head and an electrical current is applied across the brain (EFSA, 2004a:90) with the aim of inducing a grand mal seizure, which is termed an effective stun (EFSA, 2004a:92-93). Workers then have seconds to check signs of unconsciousness, shackle (attaching a chain to the animal’s hind quarters and hoisting up) and begin exsanguination (bleeding out of the animal).

There are ‘serious welfare concerns’ with electrical stunning (EFSA, 2004b:12). Incomplete stunning, due to improper placement of electrodes, is a ‘major risk’, causing incomplete stunning and painful electric shocks to the animal (EFSA, 2004b:12). Under commercial conditions one study found incorrect tong placement occurring in a high number of attempted stuns (EFSA, 2004a:94). The HSA acknowledges that in practice the correct position is ‘difficult to achieve’ and placing the electrodes ‘anywhere else’ or for insufficient time reduces stun effectiveness (HSA, n.d. [online]), risking consciousness at cutting. The British Veterinary Association (BVA) acknowledges that the effectiveness of electrical stunning is ‘largely dependent on the skill of the operator’ (BVA, n.d:45). Animal Aid’s investigations in randomly selected slaughterhouses showed numerous misplacements of electrodes (Animal Aid, 2009a:7-8) and ‘inadequate stunning’ (Animal Aid, 2009b [online]).

There are concerns that electrocution can cause an animal to be immobilised but still conscious (OIE, 2016). Current legislation dictates that electrical stunning equipment is fitted with a failsafe device disabling it from delivering a current lower than set, however the RSPCA notes this technology has ‘not proven possible’ to develop, so there is a ‘difficulty of achieving’ compliance with legislation (RSPCA, 2016:49) that aims to protect welfare. Animals should be checked to ensure they are unconscious prior to sticking (cutting the neck to severe the major blood vessels) and re-stunned if there is any doubt (BVA, n.d:39). Stun-to-stick intervals are very short at 15 seconds maximum as consciousness may be regained quickly, risking animal awareness during shackling and bleeding (HSA, n.d. and Steiner et al., 2019:17). Slaughtering a conscious animal is against UK law (with exemption of religious slaughter) as it is considered inhumane. As well as physical distress, pigs also experience physiological stress from separation from the group which is commonplace when loaded into the stunning pen (Steiner et al., 2019:17 and Hooker 2018 [online]). Further to the physiological and psychological issues it is concerning that the EFSA found that there is a lack of knowledge on brain function during electrical stun application (EFSA, 2004b:3) and welfare implications (EFSA, 2004b:13).

If done correctly electrical stunning has the advantage of causing unconsciousness immediately (EFSA, 2004b:3) however the significant welfare issues of ineffective stunning, susceptibility to human error and separation stress are widely acknowledged as significant and problematic. Electrical stunning is acknowledged as unsuitable for large throughput rates at slaughterhouses due to human error rates (Holleben, 2020).

CO2

CO2 (carbon dioxide) gas stunning is now the most used stunning method in the UK, with 86% of pigs in the UK stunned with CO2 in 2018 (DEFRA, 2018b), increased from 51% in 2013 (FSA, 2013). In 2018 around 9,245,860 pigs were CO2 stunned (DEFRA, 2018a). CO2 stunning was legalised in the UK in 1958 due to concerns surrounding electrical stunning (HSA, 2019). High concentrations of CO2 cause unconsciousness as exposure ‘depresses basal and evoked neural activity’ (Martoft 2003, cited in Steiner et al., 2019:4). The structure of a gas stunner, shown in figure one, is commonly a Ferris-wheel like design. Pigs are herded into a gondola, which then lowers into the CO2 gas pit. After a set time the crate rises and the unconscious pigs are exsanguinated.

UK law requires a minimum air concentration of 80% CO2 and that pigs remain in the stunner until dead (Welfare of Animals at the Time of Killing (England) Regulations 2015). Length of time to loss of consciousness in pigs is around 30-60 seconds (Lymbery, 2018 citing Verhoeven et al., 2016).

CO2 is aversive to pigs (Raj and Gregory, 1995 and Dalmau, 2010 cited in Steiner et al., 2019). The serious welfare problems with CO2 stunning are the pain and distress experienced in the time prior to unconsciousness. There are several reasons why this occurs. Of critical importance is the fact that CO2 and water produce carbonic acid, meaning acid will form on moist tissues on the surfaces of mammals, including the respiratory track, in high CO2 concentrations (Golledge, 2020) shown in figure two.

Atkinson et al. (2012) cites Raj and Gregory (1995) when stating that at high concentration CO2 is acidic when inhaled causing severe irritation of the eyes, nasal membranes, lungs, and pain due to presence of chemoreceptors. Pigs also experience ‘severe respiratory distress’ to all CO2 concentrations between 20-90% (Raj and Gregory, 1996:71). For reference, CO2 in normal air is very low at around 0.04% (Permentier et al., 2017). Verhoeven et al. (2016) found exposure causes abnormal breathing interpreted to be air hunger (a distressing sensation of not being able to get enough oxygen). Pigs also experience anxiety in CO2 (Hickman et al., 2016). Aversive behaviours reported in literature include vocalisations, lateral head movements, gasping, muscular excitation, eye rotation, aggression and neck extension (Atkinson et al., 2012 and Rodriguez et al., 2008 cited by Eurogroup for Animals, 2019). Escape attempts also occur (Martin, 2020). Studies have shown the extent of aversion to CO2; given choice pigs will avoid high CO2 environments to the extent they will forgo essentials which are only available within high CO2 for long periods of time, including water for 72 hours (Cantieni, 1976, cited in Raj and Gregory, 1995) and food for 24 hours (Raj and Gregory, 1995). Though its effectiveness at stunning is often stated as a benefit, research presented at the International Pig Veterinary Society Congress in 2016 raised concerns citing pigs regaining consciousness following CO2 stunning (Bolaños-López, cited by Wright, 2017).

When CO2 stunning was introduced to the UK it was considered an improvement on electrical stunning as there would be less human error (HSA, 2019 [online]). Over the years concerns regarding welfare grew and research confirmed that CO2 is aversive to pigs and ‘compromises welfare’ (HSA, 2018:3 and Martin 2020), a view now widely accepted by experts. CO2 stunning was deemed ‘not acceptable’ by the Farm Animal Welfare Council (FAWC) in 2003, advising it be phased out within five years and emphasising that government and industry should research alternative methods (FAWC, 2003:29). The European Food Safety Authority (ESFA) also called for a phasing out (Martin, 2020).  However, the government failed to act and CO2 use increased dramatically and became the industry standard (Lymbery, 2018). CO2 over electrical stunning is financially advantageous for industry as it results in less compromised meat quality (Marcon et al., 2019:4), is cheaper (Golledge, 2020), is less labour intensive (Lymbery, 2018) and faster; a 2013 survey by the Government’s Food Service Agency (FSA) found that the seven abattoirs using CO2 slaughtered about the same number of pigs as the 116 slaughterhouses using electrocution (FSA, 2013).

It is stated by many that alternatives, such as a ‘non-aversive gas mixture’, would be preferable but there are currently no commercial alternatives (HSA, 2018:3). In 2017 DEFRA and HSA announced £400,000 of funding research into an alternative (HSA, 2017), over £300,000 of which came from DEFRA (DEFRA, n.d.) which shows an acknowledgement of the need for alternative stunning. The research, looking into low atmosphere pressure stunning (LAPS), was presented recently at the international symposium Ending The Life of Animals. Despite expectations LAPS is not recommended for pigs due to numerous serious welfare findings in research including ruptured ear drums from pressure in 85% of test pigs (Martin, 2020).

Electrical and CO2: are they humane?

Both have significant welfare compromising issues, both inherent to the method and the risks known to seriously effect a proportion of animals in commercial settings, which is widely acknowledged (Bouwsema, 2019:421). The numerous issues pigs experience prior to unconsciousness in CO2 stunning is significant. Over 77,000 hours of significant respiratory distress and anxiety is experienced collectively by CO2 stunned pigs each year in the UK. This figure of over 77,000 hours is calculated by the author using the 2018 government data of 9,245,860 pigs being CO2 stunned per year and research suggesting 30 seconds of distress per pig (DEFRA, 2018a and DEFRA, 2018b). Animal Aid’s investigations found many animal welfare breaches with concerning frequency, including electrical stunning of pigs, demonstrating complacency to animal welfare by workers (Animal Aid, 2009a). The UK Government acknowledges that slaughterhouse procedures carry risk to welfare and failures do occur meaning ‘animals are experiencing avoidable pain and distress’ (FSA, 2015:5).

The debate on CO2 verses electrical stunning is essentially asking which is the least poor option for welfare. However, just because one method, in selective aspects, can be claimed to be less compromising it does not make it humane. As the evidence above demonstrates, we essentially have two poor options for stunning pigs. Compassion in World Farming (CIWF) states a slaughter method is only humane if the animal ‘dies without pain or distress’ (CIWF, 2018). Neither CO2 nor electrical stunned slaughter in commercial settings fit these definitions. The presented evidence shows neither method is ‘instant or non-aversive’, which is required to be humane (Lymbery, 2018 [online]).

The Farm Animal Welfare Council (FAWC), European Food Safety Authority (ESFA) and the World Organisation for Animal Health (OIE) all acknowledge the welfare issues outlined and also a need for change. Animal welfare experts including Dr Donald Broom, Professor of Animal Welfare at Cambridge University (Lymbery, 2018), researchers including Dr Mohan Raj and Dr Jessica Martin, animal welfare organisations including CIWF, the RSPCA (Kay, 2018) and Eurogroup for Animals which has 70 member organizations, as well as the British Veterinary Association (BVA), have all acknowledged current stunning method issues and repeatedly called for a humane alternative. Even the industry organization The National Pig Association (NPA) have welcomed new stunning method research (NPA, 2017). These multiple calls for an alternative highlight the degree of recognition by experts of the evidenced issues with current methods. Given the problems explored here it is clear that both CO2 and electrical stunning in commercial settings have inherent issues, causing significant physiological and psychological distress, and therefore are not humane on scientific grounds.

Conclusion

Both electrical and CO2 stunning have serious, evidenced welfare problems acknowledged and raised by experts, despite the image portrayed to the public. Both inherent welfare issues and error rates of the methods cause welfare compromises to occur. Electrical stunning is impractical for the fast-paced commercial setting and has welfare issues which are widely acknowledged. Acid causing CO2 stunning is deemed unacceptable on welfare grounds of due to overwhelming evidence making it incompatible with the definition of humane stunning. The practical issues identified for both arguably render each method inhumane by definition of the suffering they cause. Government bodies, experts, researchers, animal NGOs and even the animal agriculture industry acknowledge these issues and look to potential future humane stunning methods which are not yet commercially viable. For now, and for the foreseeable future, pigs in the UK face significant distress during the slaughtering process.

References

Animal Aid (2009a) The humane slaughter myth: An Animal Aid investigation in to UK slaughterhouses. Available at: https://www.animalaid.org.uk/wp-content/uploads/2016/10/slaughterreport.pdf [Accessed 11 December 2020].

Animal Aid (2009b) Humane slaughter in British abattoirs a ‘sham’. Available at: https://www.animalaid.org.uk/humane-slaughter-british-abattoirs-sham/ [Accessed 11 December 2020].

Atkinson S, Velarde A, Llonch P, and Algers B. (2012) Assessing pig welfare at stunning in Swedish commercial abattoirs using CO2 group-stun methods. Animal Welfare, 21: 487-495.

Bouwsema, J.A and Lines J.A. (2019) Could low atmospheric pressure stunning (LAPS) be suitable for pig slaughter? A review of available information.  Animal Welfare, 28: 421-432.

British Veterinary Association (BVA) (n.d.) BVA position on the welfare of animals at slaughter. Available at: https://www.bva.co.uk/media/3664/full-position-bva-position-on-the-welfare-of-animals-at-slaughter.pdf [Accessed 8 December 2020].

Compassion in World Farming (CIWF) (2018) Calling on industry to find more humane pig slaughter methods. Available at: https://www.compassioninfoodbusiness.com/our-news/2018/08/calling-on-industry-to-find-more-humane-pig-slaughter-methods [Accessed 4 December 2020].

Department for Environment, Food & Rural Affairs (DEFRA) (n.d.) Developing an alternative method to use of high concentration CO2 for the commercial stunning of pigs – MH0154. Available at: http://sciencesearch.defra.gov.uk/Default.aspx?Menu=Menu&Module=More&Location=None&Completed=0&ProjectID=19805 [Accessed 5 December 2020].

Department for Environment, Food & Rural Affairs (DEFRA) (2018a) Historical statistic notices on the number of cattle, sheep and pigs slaughtered in the UK, 2018. Available at: https://www.gov.uk/government/statistics/historical-statistics-notices-on-the-number-of-cattle-sheep-and-pigs-slaughtered-in-the-uk-2018 [Accessed 3 December 2020).

Department for Environment, Food & Rural Affairs (DEFRA) (2018b) Results of the 2018 FSA Survey into Slaughter Methods in England and Wales. Available at: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/778588/slaughter-method-survey-2018.pdf [Accessed 4 December 2020].

Department for Environment, Food & Rural Affairs (DEFRA) (2020) United Kingdom Slaughter Statistics – October 2020. Available at: https://www.gov.uk/government/statistics/historical-statistics-notices-on-the-number-of-cattle-sheep-and-pigs-slaughtered-in-the-uk-2020 [Accessed 3 December 2020].

European Food Standards Agency (EFSA) (2004a) Welfare aspects of animal stunning and killing methods: Scientific Report of the Scientific Panel for Animal Health and Welfare on a request from the Commission related to welfare aspects of animal stunning and killing methods. Available at: https://efsa.onlinelibrary.wiley.com/doi/pdf/10.2903/j.efsa.2004.45 [Accessed 1 December 2020].

European Food Standards Agency (EFSA) (2004b) Opinion of the Scientific Panel on Animal Health and Welfare on a request from the Commission related to welfare aspects of the main systems of stunning and killing the main commercial species of animals. The EFSA Journal, 45, 1-29. Available at: https://efsa.onlinelibrary.wiley.com/doi/pdf/10.2903/j.efsa.2004.45 [Accessed 1 December 2020].

Eurogroup for Animals (2019) Position paper: Stunning/killing of pigs with high concentration of CO2. Available at: https://www.eurogroupforanimals.org/sites/eurogroup/files/2020-03/CO2%20stunning%20EfA%20position%20paper%202019.pdf [Accessed 2 December 2020].

Farm Animal Welfare Council (FAWC) (2003) Report on the Welfare of Farmed Animals at Slaughter or Killing Part 1: Red Meat Animals. Available at: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/325241/FAWC_report_on_the_welfare_of_farmed_animals_at_slaughter_or_killing_part_one_red_meat_animals.pdf [Accessed 30 November 2020].

Food Standards Agency (FSA) (2013) Results of the 2013 animal welfare survey in Great Britain. Available at: https://webarchive.nationalarchives.gov.uk/20171207164502/https://www.food.gov.uk/enforcement/sectorrules/animal-welfare/animal-welfare-survey [Accessed 6 December 2020].

Food Standards Agency (FSA) (2015) Board Meeting 3 June 2015 – Update on animal welfare. Available at: https://webarchive.nationalarchives.gov.uk/20171207164502/https://www.food.gov.uk/enforcement/sectorrules/animal-welfare/animal-welfare-survey [Accessed 6 December 2020].

Golledge, H. (2020) Introduction and background to the meeting. Online Symposium – Humanely ending the life of animals. Online. 3 Nov 2020. Available at: https://www.gotostage.com/channel/81bced3dd4314165816dd8ae8b49a9b4/recording/4c44651a3672457cb307e03329bb6d58/watch?source=CHANNEL

Hickman, D.L.,Fitz, S.D., Bernabe, C.S., Caliman, I.F., Haulcomb, M.M., Federici, L.M., Shekhar, A. and Johnson, P.L. (2016) Evaluation of Low versus High Volume per Minute Displacement CO(2) Methods of Euthanasiain the Induction and Duration of Panic-Associated Behavior and Physiology. Animals, 6, (8), 45. Available at: https://www.mdpi.com/2076-2615/6/8/45 [Accessed 10 December 2020].

Holleben, K. V. (2020) CO2-stunning of pigs. An example of behaviour during induction and overview of gas concentration and other key parameters during routine slaughter of pigs in modern low stress group stunning devices. Online Symposium – Humanely ending the life of animals. Online. 3 Nov 2020. Available at: https://www.gotostage.com/channel/81bced3dd4314165816dd8ae8b49a9b4/recording/ef239ef41f6445fc87ffcf7589b7c187/watch?source=CHANNEL [Accessed 3 November 2020].

Hooker, L. (2018) Is it cruel to stun animals with carbon dioxide? BBC. Available at: https://www.bbc.co.uk/news/business-44709905 [Accessed 5 December 2020].

Humane Slaughter Association (HSA) (n.d.) Head only stunning. Available at:https://www.hsa.org.uk/electrical-stunning-of-red-meat-animals-equipment/head-only [Accessed 1 December 2020].

Humane Slaughter Association (HSA) (2017) HSA commits to new research and development to improve the welfare of pigs at slaughter. Available at: https://www.hsa.org.uk/news-events/news/post/45-hsa-commits-to-new-research-and-development-to-improve-the-welfare-of-pigs-at-slaughter [Accessed 4 December 2020].

Humane Slaughter Association (HSA) (2018) Carbon Dioxide Stunning and Killing of Pigs. Available at: https://www.hsa.org.uk/downloads/technical-notes/tn19-carbon-dioxide-stunning-and-killing-of-pigs.pdf [Accessed 19 November 2020].

Humane Slaughter Association (HSA) (2019) Welfare of Pigs at Slaughter. Available at: https://www.hsa.org.uk/news-events/news/post/60-welfare-of-pigs-at-slaughter [Accessed 3 December 2020].

Kay, A. (2018) RSPCA and CIWF demand ban on CO2 stunning for pigs by 2024. Farmers Guardian. Available at: https://www.fginsight.com/news/news/rspca-and-ciwf-demand-ban-on-co2-stunning-for-pigs-by-2024-67698

Lymbery, P. (2018) Scandal of supermarket gassing of pigs. Philip Lymbery. 10 August. Available at https://philiplymbery.com/scandal-of-supermarket-gassing-of-pigs/ [Accessed 12 December].

Marcon, A.V., Caldaraa, F.R., Oliveirab, G.F., Gonçalvesa, L.M.P., Garciaa, R.G., Pazb, I.C.L.A., Cronea, C. and Marconc, A. (2019) Pork quality after electrical or carbon dioxide stunning at slaughter. Meat Science, 156, 93-97.

Martin, J. (2020) Low atmospheric pressure stunning in pigs: Insights from analgesic and anxiolytic interventions. Online Symposium – Humanely ending the life of animals. Online. 3 Nov 2020. Available at: https://www.gotostage.com/channel/81bced3dd4314165816dd8ae8b49a9b4/recording/ef239ef41f6445fc87ffcf7589b7c187/watch?source=CHANNEL [Accessed 3 November 2020].

National Pig Association (NPA) (2017) Defra and HSA to fund research into pig stunning methods. Available at: http://www.npa-uk.org.uk/Defra_and_HSA_to_fund_research_into_pig_stunning_methods.html [Accessed 7 December 2020].

Permentier, K., Vercammen, S., Soetaert, S. and Schellemans, C. (2017). Carbon dioxide poisoning: a literature review of an often forgotten cause of intoxication in the emergency department. International Journal of Emergency Medicine, 10: 14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5380556/#:~:text=Concentrations%20of%20more%20than%2010,loss%20of%20consciousness%20in%20seconds. [Accessed 7 December 2020].

Raj, A.B.M. and Gregory, N.G. (1995). Welfare implications of the gas stunning of pigs: 1. Determination of aversion to the initial inhalation of carbon dioxide or argon. Animal Welfare, 4: 273-280.

Raj, A.B.M. and Gregory, N.G. (1996) Welfare implications of the gas stunning of pigs: 2. Stress of induction of anaesthesia. Animal Welfare, 5: 71-78.

RSPCA (n.d.) Pigs. Available at: https://www.rspca.org.uk/adviceandwelfare/farm/pigs [Accessed 1 December 2020].

RSPCA (2016) RSPCA welfare standards for pigs. Available at: https://science.rspca.org.uk/sciencegroup/farmanimals/standards [Accessed 5 December 2020].

Steiner, A. R., Flammer, S. A., Beausoleil, N. J., Berg, C., Bettschart-Wolfensberger, R., Garcí a Pinillos, R., Golledge, H. D. R., Marahrens, M., Meyer, R., Schnitzer, T., Toscano, M. J., Turner, P. V., Weary, D. M. and Gent, T. C. (2019) Humanely Ending the Life of Animals: Research – Priorities to Identify Alternatives to Carbon Dioxide. Animals, 9; 911. Available at: https://www.mdpi.com/2076-2615/9/11/911 [Accessed 15 November 2020]

Verhoeven, M., Gerritzen, M., Velarde, A., Hellebrekers, L. and Kemp, B. (2016) Time to Loss of Consciousness and Its Relation to Behavior in Slaughter Pigs during Stunning with 80 or 95% Carbon Dioxide. Frontiers in Vet. Science. Available at: https://www.frontiersin.org/articles/10.3389/fvets.2016.00038/full [Accessed 10 December 2020].

Welfare of Animals at the Time of Killing (England) Regulations 2015. Available at: https://www.legislation.gov.uk/uksi/2015/1782/contents/made [Accessed 2 December 2020].

World Organisation for Animal Health (OIE) (2016) Slaughter of Animals. Available at: https://www.oie.int/index.php?id=169&L=0&htmfile=chapitre_aw_slaughter.htm [Accessed 5 December 2020]. 

Wright, C. (2017) Issues with carbon dioxide stunning in pigs. The Pig Site. Available at: https://www.thepigsite.com/articles/issues-with-carbon-dioxide-stunning-of-pigs [Accessed 11 December 2020].