Slaughter methods: electroencephalographic (EEG) studies on spinal cord section, decapitation and gross trauma of the brain in lambs.

By means of electroencephalograms (EEG), attempts were made to determine when insensibility could be presumed in five lambs, two subjected to immobilisation by the punctilla method, two decapitated and one shot by a captive bolt in the poll region. Section of approximately 80% of the spinal cord by the punctilla method had no apparent effect on sensibility and the technique was considered to be inhumane. The EEG obtained from a decapitated bead showed no obvious change in pattern for eight seconds and subsequent changes were similar to those associated with exsanguination only. Thus no evidence was obtained to indicate that decapitation causes immediate insensibility, neither was the belief substantiated that severance of the spinal cord, during the slaughter of sheep, hastens the onset of insensibility. These results also provide additional evidence on the inhumane nature of punctilla slaughter of cattle. The animal shot with a captive bolt in the poll region, as opposed to the frontal region, showed EEG activity for 78 seconds.

Time of onset of insensibility in four- to six-week-old calves during slaughter.

The time of onset of permanent insensibility subsequent to incision of the major blood vessels of the neck was studied in one 31-day-old calf and two 42-day-old calves. Insensibility was determined from the study of electroencephalograms (EEG). Insensibility first occurred at 28, 30 and 168s, respectively. Following respiratory gasps, all three animals subsequently showed resurgences of cerebrocortical activity for periods of between 130 and 187s, and EEGs did not become isoelectric again for 116 to 300s after slaughter. These results are similar to those previously recorded in 1-week-old calves and are in disagreement with the findings of Nangeroni & Kenneth (1963) which indicated that 8-week-old calves became permanently insensible within 6·9s of slaughter.

Electroencephalographic studies of stunning and slaughter of sheep and calves: Part 1-The onset of permanent insensibility in sheep during slaughter.

The time of onset of permanent insensibility, subsequent to incision of the major blood vessels of the neck, was studied in sixteen adult sheep and five one-week-old lambs. Insensibility was determined from the study of electroencephalograms (EEG) and interpretation was based on the amplitude and pattern of fast wave signals of a transhemispheric bipolar derivation. In both adult sheep and lambs, conscious at the time of slaughter, insensibility occurred within 2 to 7 s and EEG traces became isoelectric between 10 and 43 s. In sheep which were lightly anaesthetised at the time of slaughter, EEG traces became isoelectric between 18 and 70 s after incision of the major blood vessels of the neck. In one sheep which was slaughtered by severance of the carotid artery and jugular vein on one side of the neck only, the onset of insensibility was delayed for 29 s. In the majority of animals, the electrocardiogram (ECG) continued to show a normal pattern for more than 10 min after slaughter. There was an initial rise in blood pressure in the first 5 to 7 s and it remained elevated for a further 10 to 20 s. The results of this work are discussed with reference to definition of death appropriate for statutory purposes and the implications for the humane slaughter of sheep.

Electroencephalographic studies of stunning and slaughter of sheep and calves-part 2: The onset of permanent insensibility in calves during slaughter.

The time of onset of permanent insensibility, subsequent to incision of the major blood vessels of the neck, was studied in eight one-week-old calves. Insensibility was determined from the study of electroencephalograms (EEG). Apart from one animal in which insensibility first occurred within 34 s, the first indication of insensibility did not occur until between 65 and 85 s. All animals subsequently showed evidence of periodic resurgence of possible sensibility for up to 123 to 323s after slaughter. Such resurgences were seen to be preceded by a respiratory gasp. The EEG did not become isoelectric until between 132 and 336 s. Involuntary movements of the animal and the presence of corneal and palpebral reflexes persisted for up to 300 s after slaughter. It is suggested that the marked increase in the time for insensibility to occur after slaughter in calves, compared with sheep and lambs, is due to a greater contribution of blood to the brain by the vertebral arteries in calves.

Electroencephalographic studies of stunning and slaughter of sheep and calves- Part 3: The duration of insensibility induced by electrical stunning in sheep and calves.

The duration of insensibility produced by electrical and percussive stunning was studied in sheep and calves. Insensibility was determined from the study of electroencephalograms (EEG) and concurrent observations were made of the reflexes and reactions of the animals. The effect of stunning on the circulation was assessed from electrocardiograms (ECG) and femoral blood pressures (BP). Electrical stunning of sheep by electrodes to the head only produced a period of reversible insensibility of 18-42s. This technique also caused an immediate and prolonged increase in BP. Electrical stunning of both sheep and calves by a 'head to back' method, which causes concurrent cardiac dysfunction, produced immediate and permanent insensibility associated with cessation of circulation and an immediate drop in BP. The use of a non-penetrative method of percussion stunning caused immediate insensibility and an increase in BP which persisted after exsanguination had commenced. Calves stunned with a penetrating captive bolt showed immediate and permanent insensibility and the EEG became isoelectric within 15 s.

Insensibility during slaughter of pigs in comparison to other domestic stock.

The onset of insensibility during slaughter was studied in five, 31-day-old pigs. The state of sensibility was determined from the study of electroencephalograms (EEC) which were of a bipolar transhemispheric derivation. In 3 pigs slaughtered by bilateral severance of both common carotid arteries and jugular veins, it was judged that insensibility occurred within 25 s and there was no resurgence of cerebrocortical activity following subsequent respiratory gasps. The EEGs became isoelectric within 115 s. These results are compared with previous findings by the authors that adult sheep and lambs slaughtered by similar techniques became insensible within 7 s whereas, in calves, the onset of insensibility was delayed for up to 85 s and there were resurgences of cerebrocortical activity, following a respiratory gasp, for more than 300 s. These differences in the apparent onset of insensibility in the 3 species of animal are discussed in relation to the anatomical features and possible dynamics of the blood supply to the brain during slaughter. It is concluded that for humane reasons, head-to-back electrical stunning of pigs is preferable to a head-only method.

Effects of different slaughter methods on bleeding sheep.

One hundred and sixteen sheep were slaughtered by five different methods in an attempt to determine the most practical technique which would result in rapid exsanguination without incision of the oesophagus. Techniques which involve stunning prior to slaughter were compared with the traditional New Zealand method by which fully conscious sheep are slaughtered by almost simultaneous severance of the major blood vessels of the neck and the spinal cord at the occipito-atlantal junction. Total amounts of blood lost and rates of bleeding were compared.

Cineradiography of the reticular groove mechanism.

The use of cineradiographic studies in the interpretation of how sucked liquid passes to the abomasum in young sucking ruminants is described with special reference to experimental studies in lambs and calves. The work involved an examination of the movements of stainless steel wire or clips inserted via a gastrostomy into the mucosa of the caudal thoracic oesophagus, lips of the reticular groove and margins of the reticulo-omasal orifice. This assisted the interpretation of how these structures are involved in the passage into the abomasum of sucked liquid and into the reticulo-rumen of liquid or solid ingesta or saliva swallowed independently of sucking. An understanding of contributions made by the oesophagus, reticular groove and reticulo-omasal orifice to the passage of sucked liquid into the abomasum was aided by the use of the autonomic blocking agents, atropine and hexamethonium.

Scanning electron microscope study of bacteria associated with the rumen epithelium of sheep.

Examination of the rumen epithelium of sheep by scanning electron microscopy revealed bacteria associated with the epithelial surface. Comparison of epithelial surfaces from 10 sheep revealed areas that were consistently densely covered with bacteria and other areas where the cover was consistently light. The bacterial populations were frequently of mixed morphological types, but areas populated with a single type were also observed. This finding, together with the discovery of bacterial forms not previously described in rumen contents, suggests that a specific flora may exist on the rumen epithelial surface. The functional significance of such a population is discussed.

Effects of vagotomy, atropine, hexamethonium and adrenaline on the destination in the stomach of liquids sucked by milk-fed lambs and calves.

1. The normal passage to the abomasum of liquid sucked by lambs and calves was confirmed in radiographic studies to be changed to passage of liquid to the reticulum and rumen after cervical or abdominal vagotomy.2. The effects of hexamethonium (8-10 mg kg(-1) I.V.) were similar to those of vagotomy.3. Atropine (200-800 mug kg(-1) I.V.) had either no detectable effect on the destination in the stomach of liquid sucked by lambs or caused a partial failure of the reticular groove mechanism.4. Fluid sucked by lambs passed wholly to the abomasum after adrenaline (5-40 mug kg(-1) I.V.).5. Atropine and adrenaline caused a greater dysfunction of the reticular groove mechanisms in calves than in lambs.6. Contraction of the reticular groove was observed via rumen fistulae in three lambs. Eversion of the caudal oesophagus into the reticulum which occurred when saliva was swallowed into the reticulum and rumen was not observed when liquids were sucked from a bottle.7. The continued passage to the abomasum of sucked liquid in atropinized lambs has been taken as an indication of the importance of caudal oesophageal reactions, tonic activity of the reticular groove and the atropine-resistant vagally induced opening of the reticulo-omasal orifice in the reticular groove mechanism.

Effects of stimulation of efferent fibres of the vagus on the reticulo-omasal orifice of the sheep.

1. The reticulo-omasal orifice has been observed and its activity recorded in decerebrate and spinal preparations of lambs and in lambs and sheep anaesthetized with chloralose.2. Spontaneous closure movements at about 6/min were seen, or recorded from balloons placed in the orifice in all types of preparation when both vagus nerves had been cut and after atropine, hexamethonium, phentolamine and propranolol had been given I.V.3. The effects on the reticulo-omasal orifice of stimulation in the neck of efferent fibres of the vagus nerves on either side differed according to the form of the stimulus applied.4. Threshold stimulation of the vagus nerve caused closing of the orifice which was blocked by atropine.5. Opening of the orifice and disappearance of spontaneous closing movements followed more intense stimulation of the vagus nerves.6. Vagal opening effects were obtained after atropine was given and after adrenergic opening and closure effects had been blocked with phentolamine and propranolol.