The effect of electricity on an animal

Brain activity

Whilst electricity is applied across an animal’s whole body, the body will typically be rigid and still.

If the current passes through the animal’s brain and if the parameters are appropriate for stunning, the brain is expected to show a certain type of electrical activity which, in a laboratory, can be viewed using an electroencephalogram (EEG). In Europe, EC Regulation 1099/2009 allows electrical waterbaths to be used for stunning poultry, provided the exposure of the entire body to a current generates a generalised epileptic form on the EEG. This duration of epileptic plus quiescent brain activity must last for at least 45 – 60 seconds, to allow enough time for death to occur by whichever chosen means.

If the EEG does not become epileptiform and quiescent, and for a sufficient duration, then a bird cannot be classed as effectively stunned because it may either never become unconscious or it may recover consciousness too soon, before death can occur. Similarly, if operational parameters cannot achieve unconsciousness immediately, they are unsuitable for bird welfare, even if a longer application time can result in an eventual loss of consciousness, because the bird may experience pain and distress during induction of unconsciousness.

There are interactions between the effects of the various electrical parameters that might be used to attempt to stun birds. Different combinations of parameters determine whether epileptiform activity is expressed and the degree of suppression of the EEG (ie whether a bird immediately becomes, and remains, unconscious for long enough). The electrical parameters that appear to be better at generating epileptiform and quiescent EEGs are generally high amplitude, low frequency, sinusoidal (sine) AC currents. In terms of animal welfare, high frequencies are unlikely to perform as well as low frequency currents. (In addition, the higher currents required at higher frequencies tend to still be associated with defects in carcass quality.) None of the DC parameter combinations researched so far have produced unconsciousness (as assessed by EEG) in 100% of birds.

Paralysis or electroimmobilisation

Unfortunately, paralysis or electroimmobilisation may physically resemble effective electrical stunning because muscle function is inhibited, and physical reflexes are suppressed, by the current (particularly if the current passed through the whole body, as indeed it would in a waterbath or wet plate stunner). Therefore it may be difficult to identify, using animal behaviour alone, a paralysed, conscious animal from a stunned, unconscious animal. Therefore abattoirs should follow evidence-based recommendations for animal welfare from the scientific community, when deciding how and which electrical parameters to apply to an animal, for the purpose of stunning and successfully rendering it unconscious until death supervenes.

Will the stun also kill the bird? 

The mode of current application and the electrical parameters used, can determine whether an animal will die (stun-killed) whilst unconscious, or if it has the potential to recover consciousness after the prolonged, effective stun has run its course.

Electronarcosis is a temporary, fully-reversible state. Normal brain function is disrupted for a short time only and, unless killed by another method, the animal will regain consciousness, usually within one minute. (Note: even if there is the potential for an animal to regain consciousness, this must not be allowed to actually happen (to ensure the animal’s welfare remains protected). Immediately after stunning, a killing method (eg neck cutting) must be applied to ensure the birds die (eg of blood loss) before there is any possibility of them recovering consciousness.)  Restricting a stunning current’s pathway so that it travels through only the head (brain) of an animal (eg by using head-only electrical stunning equipment), is far less likely to result in a stun-kill (ie death by electricity) than when the stunning current is also allowed to pass through the animal’s body.

A stun-kill can occur if a current passes through the heart of an animal. The muscle of the heart is more sensitive to certain, relatively low frequencies, eg 50 Hz. If a low-frequency current of a large-enough amplitude passes through cardiac muscle, an unco-ordinated condition known as cardiac ventricular fibrillation is likely to occur. The ventricles (ventral chambers) of the heart cease to beat rhythmically and instead contract rapidly and irregularly. Cardiac ventricular fibrillation (CVF) reduces cardiac output, relative to normal levels, and, without correction (eg defibrillation), CVF typically leads to cardiac arrest, which is irreversible, and the heart stops pumping blood round the circulatory system. This rapidly prevents oxygenated blood from reaching the brain (ischaemia), thereby killing the brain cells and preventing recovery of consciousness. Electrical stunning systems that apply current across the entire body, can be operated using electrical parameters that should reliably cause the majority of birds to die from a cardiac arrest. When attempting to stun-kill a bird with electricity, it is still necessary to use appropriate electrical parameters that will cause immediate unconsciousness, prior to, or simultaneous with, the occurrence of death. It is possible that insufficient current amplitude, or other inappropriate electrical parameters, can cause death without associated unconsciousness. Application of electricity in a manner that does not induce unconsciousness (eg if current bypasses the brain or if insufficient current is provided to the brain) cannot be considered humane, even if the animal dies as a result. Compared to using stun-only electrical parameters plus neck cutting, using stun-kill parameters is advantageous for animal welfare because it starts the process of dying at the same time as stunning. This reduces the risk of animals regaining consciousness before, or as, they receive a neck cut and bleed out, particularly if the neck cut is delayed and/or inaccurately performed. Death by electricity therefore acts as a ‘safety net’ for ensuring birds cannot recover if, occasionally, neck cutting is inaccurate and results in inadequate bleeding.

Immediate, accurate neck cutting is still important!

For any bird that does not die as a result of waterbath stunning, effective neck cutting remains critical. Therefore all poultry slaughtered using electrical waterbath or wet plate stunners, at all electrical parameters, should have both carotid arteries and both jugular veins severed, as standard routine practice. This may also assist with bleeding the carcass as fully and quickly as possible (particularly if the birds have experienced CVF) and may reduce the amount of blood retained in the carcass during further processing.

Next: Parameters for stunning