NR ZBJV

AU Wormuth,H.-J.; Schütt,I.; Fessel,J.

TI [Electrical stunning of slaughter poultry in accordance with animal welfare]

OT Tierschutzgerechte elektrische Betäubung von Schlachtgeflügel.

QU VetMed Berichte 2/1981, Dietrich Reimer Verlag, Berlin

PT Monography

AB The procedure of electrical stunning in a water bath using alternative currents of sinus 50 Hz is based on the principle of head-to-legs passage and commonly applied in the practice of poultry slaughter. The efficiency of this method was examined from the viewpoint of animal welfare and compared to the alternatives of head-only passage (bitemporal or comb-to-throat) and electrocution resulting in cardiac arrest due to ventricular fibrillation. The study was conducted in 377 broilers of both sexes and more than 200 layers. During a total of 366 runs of the water bath stunner, the effect of 40, 60, 70, 80, 100 and 120 V were registered with an application period of 4 - 6 s corresponding to a slaughter capacity of 3000 - 5000 animals per hour. Passage of the chickens through the water bath stunner with their backs entering the stunner first resulted in better and more reliable immersion of the birds heads than the common lateral shacking. In broilers an average current level of 46 mA (s = 12 mA) and a calculated resistance of approximately 1.6 kOhm were obtained with 70 V. At the three higher voltage levels, average currents of 64, 77 and 102 mA were measured (s = 14, 14 and 21 mA) corresponding to a nearly constant resistance of approximately 1.3 kOhm. The two lower voltages resulted in average currents of 22 and 34 mA (s = 4 and 10 mA) and a calculated resistance of around 1.9 kOhm in both. There were no significant age related differences between 4-6 week-old broilers regarding the current or the resistance. Because of their less favourable impedance conditions (rather thin and scaly legs) layers needed roughly double the voltages as broilers to obtain the same current levels. In contrast to broilers the impedance of layers could be notably reduced by wetting their legs. Electroencephalographic studies showed that current levels obtained with 70 V for 4 s in head-to-legs passage in the water bath a complete epileptiform fit occurred only in 71% of the surviving broilers. However, in only 38% of the survivors the EEG showed an isoelectric line that lasted for a minimum of 30 s after the onset of stunning, the then recommended period to open the jugular veins. An isoelectric line lasting up to 30 s after the onset of current flow was obtained by currents exceeding 45 mA in only 62 % of cases, with lesser currents in only 14%. For triggering an (although incomplete) epileptiform fit which is considered to be associated with loss of consciousness the current level around 25 mA applied for more than 4 sec is considered a certain threshold. For an application period of only 1 s a current of at least 50 mA was necessary to trigger tonic-clonic potentials. Current of less than 20 mA regardless of their application time triggered neither spasm potentials nor a depressed EEG. Complete epileptiform fits characterized by low frequency high amplitude bursts followed by an isoelectric line occurred with some regularity with currents of more than 40 mA if the application period exceeded 4 s. In the case of head-to-legs passage in the water bath, the occurrence of ventricular fibrillation has to be expected as a rule of thumb for currents of 40 mA and more, however, single deaths occurred even with currents of as little as 30 mA. Thus there is practically no tolerance range between the earliest possible occurrence of an effective stun for at least a brief period and the first possible occurrence of ventricular fibrillation. Currents above 120 mA triggered always ventricular fibrillation and thus death of the animals. Application of currents around 120 mA which can be obtained in broilers with 150 - 200 V resulted in all cases in a complete epileptiform fit with subsequent flat or isoelectric line in the EEG. The accompanying loss of consciousness was irreversible and merged without interruption into an hypoxic coma due to circulatory arrest as a consequence of ventricular fibrillation. Head-only passage of the current did never trigger ventricular fibrillation in any of the animals. Around 400 mA applied for only 1 s resulted in an immediate and sufficiently deep and lasting stun. With optimal design and application of stunning electrodes this current level may be achieved by applying 100 V. The eye (corneal, pupillar), cardiac pain and head positioning reflexes were found to be inadequate to evaluate the state of consciousness after electrical stunning by themselves. Also the comb reflex was found to be useful only with certain reservations. Thus the occurrence of an epileptiform fit that could be demonstrated and confirmed by electroencephalography remained the only reliable criterium for the induction of insensibility by electric currents. As a conclusion for practice the presently common method of electrical stunning of poultry by head-to-legs passage in a water bath with alternative currents of sinus 50 Hz of 70 V does not meet the requirements of animal welfare. From the duration of the registered epileptiform fit it could be deducted that only 30 - 40 % of the broilers had been stunned for at least 30 s. On the other hand about 10% of the animals were already killed. Although bitemporal or comb-to-throat passage of currents of 400 mA and more would lead to a good stun, they raise considerable technical problems which might present an obstacle to their introduction. Thus, the easiest way to perform electric stunning in accordance with the requirements of animal welfare would be to increase the voltage in a water bath stunner up to 150 V and more. By this the animals would be irreversibly stunned due to ventricular fibrillation. Provided a sufficiently long bleeding period (3 min) is observed detrimental effects on meat quality are not to be expected as has been shown by the results of additional studies.

AD Institut für Veterinärmedizin (Robert von Ostertag-Institut) des Bundesgesundheitsamtes, Postfach, D-1000 Berlin 38

SP deutsch

PO Deutschland

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