Model of current pathways in electrical water bath stunners used for poultry

Abstract

1. The paper explains the use and method of operation of electrical water bath stunners, and explains the possible current pathways through a single bird and through a number of birds. 2. A mathematical model has been formulated to demonstrate the effects of bird resistance and physical attitude of the bird on the current received by individual birds in a water bath stunner. 3. The model shows that readings from ammeters installed in series with commercial stunners, or the values shown on voltmeters, are not an accurate indicator or a guarantee that individual birds are effectively stunned. 4. The model demonstrates the need for a stunner to supply a constant current to each bird, rather than operate at a constant voltage where the current which the bird receives is dependant upon its own resistance.

A Review of Different Stunning Methods for Poultry—Animal Welfare Aspects (Stunning Methods for Poultry)

“…Birds have pain receptors in their legs [24] and, hanging live and conscious birds upside down by their legs in a metal shackle, which is a pre-requisite for water bath stunning, is often mentioned as one of the major welfare problems in relation to water bath stunning [25,26]. Distress and pain during shackling prior to stunning can be affected by shackle design, time from shackling to stunning, and the design of the entrance to the water-bath, where poor design can lead to painful pre-stun electric shocks.…”

“…Distress and pain during shackling prior to stunning can be affected by shackle design, time from shackling to stunning, and the design of the entrance to the water-bath, where poor design can lead to painful pre-stun electric shocks. It is known that, under the multiple bird water bath stunning system, all the birds passing through the electrified water bath will be exposed to a constant voltage, and the electrical flow through each bird will be dependent on impedance in the pathway of each bird [25,27]. This means that if a flock, for example, is of uneven size and weight, different birds will receive different amounts of current, and some birds may not receive enough to induce generalized epilepsy in the brain and some others may receive more current than necessary to induce epileptiform activity, hence suffering carcass and meat quality defects.…”

Pre-slaughter conditions, animal stress and welfare: current status and possible future research

“…Resistance depends on the number of birds at any one time in the water bath, i.e. its length, cleanliness of the water, conductivity between the shackles (earth electrode) and the birds' shanks and impedance of the birds (Schutt-Abraham et al, 1983;Bilgili, 1992;Sparrey et al, 1992). In the case of electrical stunning, rapid subsequent neck cutting is important.…”

Haemorrhages in muscles of broiler chickens

“…Subject-related variables are body size, skin hydration, population variance, pre-existing pathology or predisposition to damage and the temperatures of the skin and tissue. The location and connection of the electrodes, the electrode contact area and electrode source impedance are also important threshold-determining variables (Sparrey et al, 1992).…”

“…Passing shackled birds through a water bath and administering an electrical field to the entire body for 4-10 seconds is the most commonly applied stunning method. Most of the time a low frequency polyspike epileptic seizure is induced, rendering the birds insensitive to pain (Gregory andWotton, 1987,1989;Sparrey et al, 1992Sparrey et al, , 1993. At a high enough current the heart starts to fibrillate, killing the birds at stunning (Schiitt, 1982).…”