Evaluation of the return of reflexes (eye reflexes and nose pinch reactions) after electric stunning of slaughter hogs and comparison of electrode positions, variations of time between stunning and bleeding, and different frequencies of electric current

Die komplette Dissertation im pdf-Format (922.248 Bytes): bries.pdfElectric stunning results in paroxysmal cerebral (epileptic) seizures with temporary loss of consciousness. Death is caused either by bleeding or cardiac arrest. During routine slaughter it is difficult to tell weather animals regain consciousness or sensation. In eighteen studies involving twelve slaughter houses, 1,741 hogs were tested for eye reflexes and nose pinch reaction. Various stunning methods were used including asynchronous cardiac arrest stunning, head only stunning, and different frequencies of current. Testing was done using a modified tong pinching the hog´s nose and or nasal septum (enervated by the trigeminal nerve) at 40 to 45 sec. after initiation of current flow. The different killing methods produced dissimilar results. This can be explained by the variations in stun-stick-times, and current form influence an the epileptic fit and the probability of cardiac arrest which is also frequency dependent. In addition to the nose pinch reaction test, 1,266 animals were tested for eye reflexes. There was no regularity or correlation between the reactions of the two test, and the nose pinch test is more accurate and practical under actual slaughter house conditions. Although the nose pinch test probably does not indicate consciousness, a positive reaction may indicate the possibility of eventual return to consciousness. Therefore the goal of further investigation should be to determine which slaughter-method would lead to zero positive reactions to the nose pinch test. I. The investigated stunning method had been evaluated on the ground of recent results: 1.) Head-only stunning is considered inhumane if stun to stick time exceeds more than 21 sec.. In all cases when sticking took place after this time more than fifty percent of slaughter hogs reacted to the nose pinch test. Even when slaughter houses with head only stunning were able to stick the hogs 15 - 21sec. after current flow began, the number of positive reacting hogs was higher than after asynchronous cardiac arrest stunning. The results underline the importance of inducing cardiac fibrillation in hogs after the onset of (epileptic) seizures through the stun. 2.) In cardiac arrest stunning, when current frequencies were 300 to 500 Hz, there was reduced incidence of cardiac fibrillation. The results were similar to head only stunning. Without cardiac fibrillation, exact sticking in a lying position can be hindered and humane slaughter can not be assured. The results of this work confirms the results of other investigators concerning the shorter seizure-activity resulting from higher current frequencies. 3.) Asynchronous cardiac arrest stunning using frequency modulated current (head current:500ms from 10KHz down to 100Hz; heart- current: 500ms from 10KHz down to 80 Hz resulted in the lowest percentage of reacting pigs after stunning and sticking (nose-pinch: 4,6%; eye-reflexes: 0% (N=237)). 4.) When using asynchronous cardiac arrest stunning, it is essential to control also the heart-current frequency, strength, and duration; in order to induce fibrillation and assure humane slaughter with short stun to stick times. II. Veterinary supervision of humane slaughter should include following steps: 1.) Technical examination. The goal of the technical examination of stunning equipment should be to assure the proper function of the stunning device; including cables, electrodes and electric tongs. Continuous measurement of current can be a help (limited) in evaluating the stunning. Process evaluation can be used to analyse the conditions of pre-slaughter handling in the animals. 2.) Examination of the process of stunning and sticking, including physical evaluation of the anaesthetized animals. 2.1) Evaluation of the process and efficacy of electric stunning (seizures) Exact placement of the electrodes and continuous current flow during the stunning time should be a priority. Evaluation should include the suitability of the restraining device to assure calm entrance and low stress restraint, so that the electrodes can be placed precisely. At the end of current-flow, all animals must show typical signs of grand mal seizures, i.e. tonic-clonic spasms, no regular breathing, no reflexes, no vocalization, no reaction to the bleeding-stick, nor head righting. (In case of cardiac fibrillation, clonic contractions may be slight or unnoticeable.) 2.2) Assurance of maintaining the effect of stunning till death resulting from blood loss Measuring the stun to stick time and evaluate the workflow and - conditions is fundamental for humane slaughter. It must be assured that early sticking in the tonic state of epileptic fit is possible. Assessment of stunning and sticking could be assured by testing the nose pinch reaction or by a surface cut at nose tip or septum with a knife