Developments in humane slaughtering techniques for poultry

Stunning of animals prior to slaughter is a practice that has developed almost global acceptance as the understanding of the need to provide ‘immediate insensibility’ during the slaughter process has become widely accepted. Some countries and territories do not permit stunning before slaughter for religious or cultural reasons, but in many parts of the world it is now assumed, and in many countries, demanded by law, that stunning will take place as the first of the steps required to kill a commercially slaughtered animal (Berg and Raj, 2015).
The requirement for stunning has as its basis that animals are sentient beings (EC, 2009) and that the welfare of the animals can be best protected, according to current understanding of the cognitive and physiological basis of suffering, by induction of unconsciousness as the first and enduring stage of the process of killing. Council Regulation (EC) No 1099/2009 (EC, 2009) on the protection of animals at the time of killing defines ‘stunning’ in Article 2 (f) as ‘any intentionally induced process which causes loss of consciousness and sensibility without pain including any process resulting in instantaneous death’.
For most methods subsequent to stunning, there will be the necessity to induce a non-recoverable state (death) by exsanguination, cessation of the function of the heart or circulation, or irreversible destruction of brain and spinal cord tissue (by pithing or decapitation) so that recovery of consciousness is not possible – that is, that ‘unconsciousness lasts until death’ occurs. For these reasons, most permitted killing methods comprise a set of stunning and killing methods, which are known to be effective, for the species in question. European Food Safety Authority (EFSA) has recently published guidance on the assessment criteria for studies evaluating the effectiveness of stunning methods regarding animal protection at the time of killing (EFSA, 2013). The eligibility criteria that must be fulfilled to achieve the required definition of ‘effective stunning’ in the EU (EFSA, 2013) are
a. Immediate onset of unconsciousness and insensibility; OR
b. Absence of avoidable pain, distress and suffering until the loss of consciousness and sensibility
c. Duration of the unconsciousness and insensibility (until death).
In Europe, the welfare of poultry at the time of killing is protected by Regulation (EC) 1099/2009 (Anonymous, 2009). Article 4 on stunning interventions regulates that ‘animals shall only be killed after stunning in accordance with the methods and specific requirements related to the application of those methods set out in Annex I of the Regulation’ and ‘that the loss of consciousness and sensibility shall be maintained until the death of the animal’.
Furthermore, the methods referred to in Annex I of Regulation EC 1099/2009, which do not result in instantaneous death shall be followed as quickly as possible by a procedure ensuring death, such as bleeding, pithing, electrocution or prolonged exposure to anoxia. The methods for stunning and killing poultry permitted by this regulation are (in some estimated order of commonality of use in the EU) (EC, 2012);
• Electrical water bath stunning (81% of broilers [EC, 2012]) – the birds move through a water bath suspended by the legs on a shackle, and their heads are immersed in water which carries the stunning current from the head through the body to the electrical contact in the shackle.
• Gas stunning (19% of broilers) – usually progressing to gas killing through hypoxia – use of gases, commonly carbon dioxide, or carbon dioxide in association with inert gases such as Nitrogen, Argon, or inert gases only.
• Head-only electrical stunning – the use of manually operated ‘tongs’ which produce current flow across the head, and are most commonly used in turkeys, ducks and breeder poultry.
• Penetrating and non-penetrating captive bolt, firearms – used for emergency on farm or casualty killing of birds on farm, and sometimes used for killing of larger birds including turkeys and ostrich.
• Head-to-body electrical stunning – theoretically possible for use on poultry, applying the current from the head to electrodes on the body and inducing both a stunned state and cardiac arrest – predominately used in sheep, cattle and pigs.