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Welfare of Pigs at Slaughter

10 January 2019

The Humane Slaughter Association (HSA) – caring beyond the farm gate

It’s hard to believe today but, when the HSA was founded in 1911, there were no laws protecting animal welfare at slaughter.

In 1928 there were over 20,000 private slaughterhouses in England, to which no-one involved in animal welfare had the right of entry, except with the permission of the owner.  There was no requirement for those carrying out the slaughter to be assessed as to their fitness for the task, nor for their equipment to be inspected as to its suitability.

All animals slaughtered for food were bled by cutting their throats with a knife – a process known then and now as “sticking”.  Large animals, mainly adult cattle and pigs, which were difficult to manually restrain prior to sticking, were therefore usually stunned first using a large, heavy hammer-like instrument known as a “poleaxe”.  Smaller animals such as sheep and pigs were more manageable and so stunning was not considered necessary. The pain and suffering endured by these animals can only be imagined.

Since its foundation over 100 years ago, the HSA has led and/or contributed to major changes in attitudes towards animals, with scientific and technological developments resulting in huge improvements in methods for slaughter or killing.  One of the current projects that the charity is undertaking is in relation to a potentially more humane way of stunning pigs using a Low Atmospheric Pressure System (LAPS). 

Many will have seen the recent media coverage relating to the use of CO2 gas to slaughter pigs.  In actual fact, The Slaughter of Pigs (Anaesthesia) Regulations came into force on 1 December 1958 which legalised the use of CO2 stunning for pigs.  This new method had been developed in the USA and Denmark and used a mixture of 65% CO2 in air to render pigs unconscious before slaughter and until death from exsanguination. The charity’s General Secretary, Miss Dorothy Sidley, observed pigs being anaesthetised in a plant in Northern Ireland.  The gas concentration was maintained automatically and a visible and audio signal warned operators if the concentration varied beyond the programmed limits.  At the time of its introduction, it was considered an improvement on electrical stunning and less open to human error.  Notwithstanding, the HSA persuaded the Ministry of Agriculture to include a protective clause in the Regulations requiring a captive-bolt pistol to be available at all times in case of an emergency.  Over the years, there have been concerns about the humaneness of CO2 and research established that pigs find exposure to high concentrations of the gas aversive.

In September 2013, The Humane Slaughter Association held a workshop in London to discuss the use of Low Atmospheric Pressure Stunning (LAPS) for food animals at slaughter. The HSA's purpose for organising the meeting was to learn of the development and use of this new system, discuss scientific findings relating to humaneness, and consider its potential for wider use and what further research might be needed relevant to this. The meeting was attended by participants with an interest in the topic from scientific, technical, animal welfare and legislative perspectives.

In 2017 the charity organised a seminar on Controlled Atmosphere Stunning (CAS) methods to examine the latest developments in research into these methods.  The meeting was oversubscribed with speakers and attendees from as far afield as New Zealand, Canada and the USA.  Amongst other issues the meeting highlighted the importance of air-hunger as an extremely unpleasant physiological state, the need for high-quality science in this area and the practicalities of translating scientific information and advances into changes in legislation and practice.  As part of its commitment to ensuring the welfare of animals at slaughter, the HSA announced at this conference a collaboration with Defra to provide funding of up to £400,000 for research into alternatives to carbon dioxide for the humane slaughter of pigs.

The funding was eventually awarded to a consortium led by Dr Dorothy McKeegan at the University of Glasgow, with collaborators at University of Edinburgh (Dr Jessica Martin) and SRUC (Dr Emma Baxter), who are examining the animal welfare impacts of Low Atmospheric Pressure Stunning (LAPS).  LAPS works by gradually reducing the atmospheric pressure in a sealed unit, which renders animals unconscious and kills them by anoxia.  This method has just received approval for use in Europe to kill broiler chickens but needs to be tested in pigs to determine whether it is more humane than existing methods for stunning or killing them.  The study will test the physiological and behavioural responses of pigs to LAPS, and compare them to responses of pigs exposed to carbon dioxide, allowing a comparison of the animal welfare impacts of the two methods.  Initial trials have begun with final results of the two-year study expected in 2020.

As a charity, the Humane Slaughter Association relies on voluntary donations and legacies to fund vital and important work like this – work which has the potential to make a huge and long-lasting difference to the welfare of animals at a time when they are at their most vulnerable.  Please support our work with a donation – you can donate online at or by telephoning the office 01582 831919.  Thank you.

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