The live electrode-water-bird interface

Water depth

A waterbath must be capable of precise vertical adjustment. A hydraulic lifting system may be required to quickly raise or lower a waterbath whilst it is filled with water. If a large proportion of birds avoid the electrified water it is likely the waterbath height, and perhaps also the water level, need adjusting. The height of a waterbath and the depth of the water within it must be regularly monitored by abattoir personnel and be adjusted, as necessary, to allow full submersion of the head, including the eyes and cranium (the part of the skull encasing the brain), of all birds in the batch. In ducks, when only the beak and crop are immersed, disruption of normal brain function is typically less profound and this may be due to the brain receiving a lower proportion of the current that is passing through the whole bird. Unfortunately it may be difficult to achieve complete submersion of the heads of waterfowl (the heads appear to involuntarily float at the water’s surface). Therefore it may be important to install a device that submerges the cranium of each duck or goose, eg a neck extender - although these may have limited success.

Birds may be submerged up to the rostral edge of each wing (ie shoulder level: Figure 1), if this ensures immersion of the head of the smallest bird in the batch being processed. In Europe, birds must be immersed up to the base of the wings (EC Regulation 1099/2009). However, care should be taken if birds are immersed deeper than the shoulders, because there may be a risk of current bypassing the head and brain and birds may not be rendered unconscious, although this is yet to be scientifically investigated.

If a shackle line is moving at a fast speed with a large number of birds per minute, such that the water is pulled from the entrance of the waterbath towards the exit, causing birds’ heads to not be fully submerged at the start of stunning, then the water level should be raised to counter this effect and ensure complete submersion of the heads for the entire length of the waterbath.

Wet plate electrical stunning systems

Some electrical, whole-body stunning systems for poultry do not operate with a deep ‘bath’ of electrified water. Instead, they may operate with a shallow bath of water and/or simply run water over a live electrode (hence ‘wet plate’), with which the birds’ heads make direct contact (typically the sides of their heads are dragged over the electrode as the shackle line advances). In most cases, the principles that apply to waterbaths also apply to wet plate systems, eg maintaining good electrical contact, including the ability to adjust the height of the stunner to ensure the birds’ heads make full contact with the electrode.

Wet plate systems have been found to offer inconsistent contact and may put birds at risk of pre-stun shocks. Therefore if they are used, operators must ensure every bird’s head makes full, continuous contact with the live electrode in the appropriate manner and before any other body part touches the electrode. Despite offering direct physical contact between a bird’s head and the electrode, wet plate systems appear unable to overcome the aforementioned variation in resistance between sexes of broiler chickens.

Directing the current through the brain 

Electrodes must be placed so the target organ (brain) lies between them. There must not be any opportunity for current to bypass the brain and travel instead through other (eg less resistive) body tissues. For example, if a bird’s head remains above the electrified water or does not contact the electrified wet plate, but its chest is the first point of contact with the water or the plate electrode, then the chest will still complete the electrical circuit and current flow may be evident from the immediate cessation of movement in the bird and a rigid posture. However, it is possible the brain is not in the pathway of current flow and there is a significant risk the bird may experience electroimmobilisation and merely be paralysed whilst remaining conscious and capable of suffering extreme pain and distress. This is a possibility in all species, but is a particular risk for some species which have a tendency to swan-neck on a shackle line (Figure 10). Despite this risk, it is possible for a bird’s entry into electrified water to be swift and effective if an entry ramp is used; but flocks must be monitored to ensure this is the case. If it is not, neck extenders can also be used with long-necked species, to guide the heads completely under the electrified water almost immediately, although these may have limited success. The installation of neck extenders must be carefully planned so they do not obscure viewing for the assessment of the immediacy of stunning and the absence of pre-stun shocks. Once installed, neck extenders must be monitored to ensure all birds’ heads are indeed pushed below the neck extender (and not trapped above it, which may cause pre-stun shocks to the wings or chest and electroimmobilisation). For further details on neck extenders please read the HSA Guidance Notes No.7 on 'Electrical waterbath stunning of poultry'.

Figure 10. A swan-necking duck on a shackle line. Compared to the other ducks, with their necks and heads hanging down, the duck second from the right has curled up its neck so the chest is below the head. If its chest makes contact with the electrified water before the head, there is a risk the duck may experience current flow without loss of consciousness because the brain is unlikely to be in the path of current flow. This will be inhumane.

The submerged electrode

To maximise the current amplitude received by the birds, the submerged electrode must always be as close as possible to the birds’ brains, both horizontally and vertically (Figure 1). In terms of the horizontal, the submerged electrode must extend across the entire length and width of the bottom of the waterbath. In terms of the vertical distance, it is ideal if birds’ heads touch the live electrode, as long as the heads are also simultaneously and completely submerged under the electrified water. The live electrode should always be within 5 cm of the beaks of the birds to ensure their whole heads are exposed to a sufficient current.

Water conductivity

At concentrations of even 0.1% weight/volume, food-grade salt can be added to the water and should dramatically increase conductivity. Although adding higher concentrations of salt may further reduce resistance, the effect is marginal beyond 1% and the voltage required is unlikely to decrease much further. So adding salt, even in large concentrations, may not improve a system that is inappropriately set-up, nor can it compensate for using a voltage that is insufficient to deliver a minimum recommended current per bird. Further, 20 – 30 minutes after adding salt to fresh water, the gain in conductivity may be lost.

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

Maintaining a single current pathway in each bird

In the interests of animal welfare and meat quality, try to limit the risk of the formation of current pathways between adjacent shackled birds. Such alternative electrical pathways may cause additional variation in the current each bird receives. Therefore, birds should be shackled with sufficient space between one another so they do not touch.

Obstructions to birds’ passage through a waterbath

Birds must be able to pass through a waterbath without impacting against, or being hindered by, any obstacles. For example:

• Make sure the submerged electrode is not of a size or shape, or in a position, that obstructs birds’ heads from swinging swiftly into the water, or from being fully submerged.
• The width of a waterbath must comfortably accommodate all the types of birds it is used for, so their heads cannot become trapped against the side panels (Figure 11), which can prevent the head from entering the water.
• If any bird escapes from its shackle and is stood in the waterbath, then, depending on its position in the waterbath, it may prevent other shackled birds from being immediately stunned. The escaped bird may a) alter the current flow through shackled birds and b) may be at risk of receiving electric shocks via contact with shackled birds as they pass. The escaped bird must be removed as soon as safely possible. The shackling of conscious birds must immediately cease and the shackle line must stop. Birds which have already begun passage through the waterbath must immediately receive a neck cut, if they are stunned. The electrical supply can then be switched off and the escaped bird carefully retrieved. The escaped bird must be immediately stunned and killed with a humane back-up method; it must not be reshackled.

Figure 11. A broiler chicken's head is trapped against a side panel of a waterbath. The bird will experience current flow because its body is in-contact with the electrified water; however it may not be rendered unconscious and insensible to pain because its head (and therefore brain) are not in the water. The waterbath side panels are too close together and must be moved apart to prevent this situation occurring.

Next: The leg-shackle-earth interface