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Studies to develop a method of recording the correct level of pressure to tong electrodes to ensure an effective pre-slaughter stun in pigs. - MH0126

A steering group will be formed to develop each objective within this proposal. The steering group will consist of (a) members of the Division of Farm Animal Science, University of Bristol, (b) John Goodman, (engineer) Industrial Strategy Consulting, MLC, (c) Gerry Lewcock, (engineer) BEL Developments Ltd., and (d) a member of the Farm Animal Welfare Division, DEFRA.

Objective 01 to modify an existing pair of stunning tongs that will enable the application pressures, voltages and currents to be recorded during the commercial stunning of pigs. The stunning tongs developed during MH0111 are heavy and unbalanced and limited to record pressure from a single electrode under experimental conditions. A commercially available German stunning tong (Figure 1.) is currently under test and will be modified to contain pressure transducers mounted beneath the electrodes to record the pressure of application from both contact points. These tongs are lightweight (2.8 kg) but robust with aluminium arms and with dimensions of 750 x 270 mm, are suitable for the size of animals slaughtered in the UK. The electrode design is consistent with the preferred choice of electrode (MH0111 final report).

Objective 02 To measure the pressure of application, voltage and current during the commercial stunning of pigs using the modified stunning tongs developed in objective 01 and to determine the effect of electrode cleanliness on current transfer at both low and high voltage. The applied pressure, voltage and current profiles will be recorded from the commercial use of the prototype tongs produced in objective 01, in a minimum of 5 pig abattoirs. The operation of the tongs with a minimum of 30 pigs per slaughterman will be recorded for as many different slaughtermen as practicable per abattoir. However, the selection of 5 abattoirs will enable a minimum of 15 slaughtermen (approximately 3 per abattoir) to be assessed. We would judge that the data generated from 15 slaughtermen would give a reasonable estimate of variability between individuals and also allow an estimate of variation between abattoirs to be made.

Objective 03 Analysis of the data generated in objective 02, to determine a pressure threshold that can optimise the head-only stunning of pigs and to determine an algorithm to be used in a stun monitoring system. At present, the high voltage isolated output to stunning tong electrodes is switched using a low voltage sensing circuit that measures the resistance between the electrodes and if this resistance falls below a pre-set value, the ‘stunning’ voltage is applied.

The effect of tong electrode condition on current transfer will also be analysed under objective 03. This should reinforce the rationale for the introduction of an electrode cleaning method by comparing the impedance to current flow when worn and tarnished electrodes are contrasted with dirty electrodes and/or clean, new electrodes at 12 volts DC (a low voltage used to measure the impedance of the load for switching purposes) and at 300 volts AC (a high voltage above the threshold voltage necessary to quickly break down the initial high impedance of living tissue). The results may also reinforce the change from low voltage switching to the use of pressure sensing to switch “on” the stunning voltage.

Objective 04 An interim report will be provided by the Steering Group providing an assessment of the effect of pressure and cleanliness at high and low voltage on the stunning current profile and hence the effectiveness of the stun to assess whether additional work is needed to investigate methods of electrode cleaning.

Objective 05 To study the commercial methods employed to clean and maintain stunning tong electrodes. This will involve an assessment of current practice e.g. practical measures to maintain electrode condition and written procedures, in a total of 12 pig abattoirs. In addition the opinion of management will be obtained to assess the cost implications of both the implementation of a method of cleaning tong electrodes and the replacement of low voltage switching with pressure sensing as a method of controlling the application of stunning voltages.

Objective 06 The Steering Group will evaluate the output from objective 05 to produce a recommendation of the best method of cleaning stunning tong electrodes. This objective will combine the engineering expertise of colleagues from the MLC and B.E.L. with the insight obtained from membership of ”the stun assurance system working party,” advice from the Health & Safety Executive and the results from objective 05 to develop a concept for the optimum method for cleaning stunning tong electrodes. It is proposed that these recommendation can be used by DEFRA to advise the abattoir equipment supply industry of proof of principle.

Objective 07 A list of best practices will be produced that will enable technology transfer to the pig industry.
1) To design and construct an experimental pair of stunning tongs that wil enable the application pressures, voltages and currents to be recorded during the commercial stunning of pigs.
2) Analysis of the data generated in obj 1, to determine a pressure threshold that can optimise the head-on stunning of pigs and to determine an algorithm to be used in a stun monitoring system.
3) To design and build a prototype pair of stunning tongs that will enable the pressure of application to be routinely monitored with normal commercial use.
4) To evaluate the stunning tongs developed in obj 3 in five pig slaughterhouses.
5) To develop a commercial stunning tong cleaning station that will ensure that stunning tong electrodes are maintained in good condition.
6) To take the results from the previousl objectives to a commercial manufacturer to enable the benefits to become a commercial reality.
Project Documents
• Final Report : Final Report   (2682k)
Time-Scale and Cost
From: 2003

To: 2005

Cost: £180,763
Contractor / Funded Organisations
University - Bristol
Animal Welfare              
Plants and Animals              
Fields of Study
Animal Welfare