Bleeding

Neck cutting is the final step of the slaughter process. Its purpose is to bring about bleeding and the death of a stunned bird.

Even if the intention is to use electrical parameters that will cause the majority of birds to die in a waterbath, it may be unlikely that 100% of birds will experience cardiac arrest, particularly if using current amplitudes lower than those in Table 5 and/or if using a constant voltage stunner. Consequently, any surviving birds are reliant on a follow-up killing method (ie neck cutting) being performed thoroughly and quickly, to prevent recovery of consciousness. Therefore, birds should not be passed through an electrical waterbath unless they can be immediately checked for effective stunning and then immediately bled. Only after a bird has been checked and confirmed to be effectively stunned, should its neck be cut.

The blood loss must be rapid and profuse in order to achieve a quick death. Ideally, the cut must sever all the major blood vessels in the neck of a bird, particularly those that supply oxygenated blood to the brain, the most important of which are the two common carotid arteries. By preventing oxygenated blood from reaching the brain, ischaemia will set in and the brain cells will die, preventing recovery of consciousness. Ideally, slaughterpersons should also sever the two jugular veins, even though they carry deoxygenated blood away from the brain.

Time to irreversible unconsciousness and time to brain death

There must be insufficient time for recovery of consciousness, before permanent loss of brain function due to lack of oxygen. Following electrical stunning of broiler chickens, severing both common carotid arteries and both jugular veins will achieve a quiescent EEG (a sign of continuing effective stunning) within approximately 15 – 30 seconds. This is quicker than after severing only one carotid artery and one jugular vein, which in some cases can take 1 – 2 minutes to achieve a quiescent EEG, particularly as the frequency of the current increases. Compared to severing only one carotid artery and one jugular vein, severing both carotid arteries and both jugular veins will also reduce the proportion of birds displaying behavioural indicators of consciousness. (Note: although severance of both carotid arteries is a rapid means of bleeding a bird, it cannot be used to compensate for inappropriate electrical parameters, eg those that do not provide a sufficient duration of unconsciousness.)

In Europe, if waterbaths operate at ≥ 51 Hz, both carotid arteries, or the vessels from which they arise, shall be systematically severed (EC Regulation 1099/2009). Whatever stunning parameters are used, good practice for animal welfare and meat quality is to immediately sever both carotid arteries and both jugular veins as an absolute minimum, in all birds. This policy may reduce the risk of recovery of consciousness for any birds that are temporarily stunned (including because if variation in resistance causes some birds not to receive a high-enough current amplitude to cause death, even if the abattoir intends so).

Please refer to the HSA Guidance Notes No.7 on ‘Electrical Waterbath Stunning of Poultry’ if additional detail is required.

Locating and identifying the carotid arteries and jugular veins

The carotid arteries lie embedded in the muscle of the neck but, depending on the species of poultry, they vary in how close they lie to the cervical vertebrae (the neck bones). In chickens, geese and guinea fowl, near the head, the arteries are typically visible on the surface of the muscle (Figure 16). Whereas in turkeys, the arteries remain hidden underneath the surface of the muscle, even near the bird’s head. Ducks have very deeply embedded arteries and these cannot be seen from the surface of intact neck muscle. In all species, the carotid arteries are most easily accessible for cutting from the ventral aspect (underside) of the neck, ie the throat.

Figure 16. Top: schematic of a bird's head and throat, with the ventral (lower) jaw, trachea and oesophagus removed, to show the position of the common carotid arteries and external jugular veins and the ideal location to perform a ventral neck cut to sever all four major blood vessels.

Bottom left: dissected throat of an end-of-lay chicken to show the major blood vessels. The external jugular veins lie just under the skin and have thin walls so blood can be seen within them. The carotid arteries are in the neck muscle and have thick walls so the blood inside cannot be seen. (The oesophagus and trachea cannot be seen because they are pulled round, underneath the bird for the purpose of the photograph.)

Bottom right: dissected throat of a turkey to show the carotid arteries (white tubes) embedded within the neck muscle. The muscle has been cut to expose the arteries. (The jugular veins cannot be seen because the skin is folded underneath the bird for the purpose of the photograph.)

Next: Performing an effective neck cut