Assessment of the humane aspects of electric lancing of whales by measurement of current densities in the brain and heart of dead animals.

The potential physiological effects of the electric lance are assessed, as used in Japanese whaling operations. Current densities are measured in the brains and hearts of six whales to which a controlled current of 5 A is applied by two electrodes inserted at various sites in the carcasses. The whales vary in size from 1.8 m (22 kg) to 16 m (40 t). The minimum current density in the brain necessary to cause depolarisation of neurones is estimated to be 10 mA cm-2 and to cause ventricular fibrillation is estimated to be 0.5 mA cm-2. No current densities exceeding 4.8 mA cm-2 are recorded in the brain. Very few recordings of current density from the heart are above 0.5 mA cm-2, and they occur only when electrodes are in optimal positions. When electrodes are placed as in whaling operations, no whale over 3 m in length would receive current densities in the heart or brain sufficient to cause permanent dysfunction. It is concluded that electric lancing is ineffective as a secondary method of killing whales and that the current densities recorded could cause pain and suffering to an already distressed animal.

Differences in behaviour between sheep and cattle during slaughter.

Three fully conscious lambs, two adult sheep, five calves and one young bull were slaughtered by bilateral severance of the carotid arteries and jugular veins while standing. The calves and bull exhibited apparently coordinated body movements for much longer than the lambs and adult sheep. Other signs assumed to be associated with cerebral hypoxia, such as clonic convulsions and pupillary dilation, occurred earlier in the sheep than in the cattle. Although there is no single definitive method for assessing the onset of insensibility in animals during slaughter, it is believed that these findings support previous more objective encephalographic studies which indicated that there are clear cut differences between sheep and cattle.

Differences in blood supply to the cerebral cortex between sheep and calves during slaughter.

Using methylene blue boli, injected via an intracardiac catheter, the blood supply to the brain in two one- to 10-day-old calves and three adult sheep was studied during and after severance of the common carotid arteries and jugular veins. Passage of dye through cerebral vessels could not be observed in the exposed cerebrum of sheep after bilateral severance of major blood vessels. When vessels were severed on one side only, the passage of dye was noted for at least 53 seconds. In calves, after bilateral severance, sequential boli of dye could be detected passing through the cerebral vessels for more than 100 seconds. These results provide an explanation and support for the belief that there are major differences in the onset of insensibility between sheep and calves subsequent to severance of the common carotid arteries and jugular veins. The differences in blood supply to the brain which were demonstrated could be accounted for by differences in the blood supply to the brain by the vertebral artery in sheep and cattle. The effects of slaughter on the blood supply to the eye are discussed as a possible explanation of the disparity between results of studies in this general field which have used retinal responses in their investigations and those which have not.

Leptospirosis and the maintenance host: a laboratory mouse model.

A laboratory mouse model was used to investigate the criteria that have been suggested as differentiating between a maintenance host and an accidental host for a particular leptospiral serovar. The comparative studies were conducted with serovars ballum, pomona, balcanica and hardjo. The relative pathological response, ratio of serological to bacteriological prevalence, level of serological response, age-susceptibility to infection and demonstration of artificial intraspecies transmission were found to be inadequate criteria with which to differentiate maintenance and accidental hosts for a particular serovar. The demonstration of natural intraspecies transmission was considered to be the definitive criterion for differentiating such hosts. In the light of the results obtained from the laboratory mouse model and the results obtained from field studies, a maintenance host may be defined as an animal which is capable of acting as a natural source of leptospiral infection for its own species. A maintenance population may be defined as a population of a species of animal which acts as a continuous reservoir of a serovar in a specific ecosystem.

Changes in the release of amino acid neurotransmitters in the brains of calves and sheep after head-only electrical stunning and throat cutting.

In calves aged two to five months, throat cutting resulted in an increase in the concentration of the amino acid neurotransmitters glutamate and aspartate in the brain. Electrical head-only stunning by itself also increased the concentrations of these two neurotransmitters. The levels induced by stunning resulted in a seizure state characterised by epileptiform-like activity in the electroencephalograph. Combing head-only stunning with throat cutting within 10 seconds of the stun had a synergistic effect upon glutamate and aspartate, increasing their concentration by a greater amount and more quickly than either procedure on its own. An irreversible loss of brain function also occurred more quickly than after throat cutting alone. The administration of glutamate and aspartate receptor antagonists before the throat cutting lengthened the time to the loss of brain function in a dose dependent manner. Similar changes were observed in sheep but they occurred much more quickly than in cattle.

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.

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.

Rabbit mortality survey.

In a survey of mortality in 2224 rabbits of up to 12 weeks of age, drawn from 10 production units, neonatal mortality was important with 111 stillbirths and 175 deaths in the 1st week of life out of a total of 457 deaths in the whole survey. There was a low overall incidence of death from respiratory and enteric disease during the period of study.

The serologic and cultural prevalence of Leptospira interrogans serovar balcanica in possums (Trichosurus vulpecula) in New Zealand.

In a serologic and cultural survey of 127 brush-tailed possums (Trichosurus vulpecula) occupying pasture land in New Zealand, leptospires of the Hebdomadis serogroup were obtained from 48 (38%) of the animals sampled. Eight isolates were identified by cross-absorption agglutin ation studies as being Leptospira interrogans serovar balcanica. There was a marked age difference in prevalence with 41 positive cultures from 64 mature adults (64%) and no recoveries being made from juveniles. Isolation of leptospires was aided by the use of a new technique involving the homogenation of whole kidneys in gamma sterilized plastic bags in a "Coleworth Stomacher". The use of this apparatus allowed the processing of whole kidneys and the technique was efficient in both the recovery of leptospires and the prevention of contamination. In view of the fact that serovar balcanica has been recorded previously only in East Europe in man, cattle and pigs, the high prevalence of infection in a wild animal population in New Zealand is an interesting development in the world distribution of this serovar.

Leptospirosis in free-living species in New Zealand.

A total of 1296 free-living mammals and birds of 12 species was examined for serologic and bacteriologic evidence of leptospiral infection. Endemic infection with serovar ballum was found in several introduced species of mammals. Endemic ballum infection is not recognized in the same species in Great Britain, their country of origin. Possums (Trichosurus vulpecula) were found to have a high prevalence of infection with balcanica, a serovar that has been isolated from possums in Australia and from cattle, pigs and humans in Eastern Europe. Free-living lagomorphs and deer were both serologically and bacteriologically negative. Waterfowl were bacteriologically negative, and only one serological titre was found.

The occupational hazards of leptospirosis in the meat industry.

The sera from 1215 meat inspectors and 1248 meat workers were examined for the presence of agglutinating titres of 1:24 or greater to the serovars of Leptospira interrogans known to be endemic in New Zealand. Although 10 percent of meat inspectors and 6.2 percent of meat workers were seropositive, only 9.5 percent of meat inspectors and 4.1 percent of meat workers had titres compatible with occupational exposure to domestic stock. The subgroup of meat workers with the highest prevalence of agglutinins (10.4 percent) were those working on the slaughter floor, and the inspection and processing of pigs were shown to be the most important risk factors. More than 50 percent of those with a history of medically confirmed leptospirosis in the past ten years still had detectable titres. Although the results of this survey demonstrate that leptospirosis is a definite occupational hazard in the meat industry, the risk is threefold less than for dairy farm workers and pig farmers.

Risks of contracting leptospirosis on the dairy farm.

The sera of 460 people associated with farming were examined for evidence of leptospiral agglutinins. Of these, 308 were dairy farm workers, 62 percent of whom were from the Waikato. Forty-four percent of dairy farm workers, 8 percent of sheep and beef farmers and 25 percent of pig farmers ware seropositive. Of the 137 seropositive dairy farm workers, 65 percent had titres to serovar hardjo and 53 percent to pomona. There were no significant differences between the serological prevalences of workers in different geographical regions. Analysis of factors significantly associated with seropositive workers included; being male, a previous history of medically confirmed leptospirosis in the worker, a clinical history of leptospirosis in the cattle, the size of the milking herd, the type of milking shed, and vaccination of the herd against leptospirosis. These findings indicate that the incidence of leptospirosis in dairy farm workers can only be effectively controlled by reducing the prevalence of infection in dairy cattle.

Leptospirosis of pig farmers: the results of a serological survey.

Serum samples were examined from 70 people working or resident on 41 pig farms within a 50 km radius of Palmerston North. Of the 65 people with occupational pig contact, 20 (31 percent) had microscopic agglutination titres of 1:24 or greater to one or more serovars of Leptospira interrogans, the majority of which were to pomona, the pid adapted serovar. There were significant positive associations between those people with a titre and those with a history of previous diagnosis of leptospirosis by a medical practitioner and the number of breeding sows and fattening pigs on the property. Pig farmers are at similar risk to contracting leptospirosis as dairy farmers, but the major serovars involved are different, and the total population at risk is less. Further evidence is provided that titres to leptospiral agglutinins can persist in humans for longer than ten years.

Leptospirosis in meat inspectors: preliminary results of a serological survey.

A serological survey of leptospirosis among more than 1000 meat inspectors, from meat works throughout New Zealand, revealed a serological prevalence at a minimum serum dilution of 1:24, of 10.2 percent. Eighty-five percent of serological reactions were to serovars pomona and tarassovi. A highly significant correlation was demonstrated between the serological prevalence of these serovars and the inspection of pigs. Evidence is provided to substantiate the use of titres as low as 1:24 as an indication of previous leptospiral infection. Forty-two inspectors reported medical evidence of previous clinical infection with leptospirosis. Analysis of those who still exhibited a serological response and their individual case histories, indicated that detectable titres of leptospirosis can exist for up to 10 years.

The magnitude and duration of titres of leptospiral agglutinins in human sera.

Sixty-nine meat inspectors with titres of leptospiral agglutinins ranging from 1:768 to 1:24, were re-bled and reexamined periodically over a period of 53 months. Some individuals maintained titres of 1:384 and 1:192 for at least 30 months and others with initial titres of 1:48 and 1:24 maintained such titres for 53 months. Only six, of 63 initially seronegative (less than 1:24) meat inspectors, seroconverted during the period of study. The magnitudes of titres at a single sampling from each of 162 people, with previous histories of medically confirmed leptospirosis, were analysed in relation to time elapsed since initial diagnosis. Some individuals had titres of 1:192 seven years after infection, while others had lower titres after more than 20 years. Conversely, 12% of the population was seronegative two years after infection. These results indicate that it is not possible, from the results of a leptospiral agglutination test, to estimate retrospectively the time at which infection may have occurred. In a small proportion of individuals recently affected by leptospirosis, it will not be possible to demonstrate a change in agglutinating titre.

Non-penetrative percussion stunning of sheep and calves.

Attempts were made to stun lambs, adult sheep and calves by a non-penetrative percussive method. Using an adapted Cash pistol, with a concave padded impact head, impulses were produced which effectively stunned 96% of lambs but induced brain haemorrhages in up to 7% of the animals. The signs and duration of an effective percussive stun were observed and recorded. Calves were readily stunned by percussive methods but brain haemorrhages frequently occurred. Impulses sufficiently large to stun adult sheep, with a non-penetrating impact head, were produced from an adapted Hantover pneumatic cattle stunner. Comparative trials, using electrical and percussive stunners, demonstrated a significant decrease in the prevalence of blood splash in lambs stunned by percussion.

Energy requirements for the penetration of heads of domestic stock and the development of a multiple projectile.

The forces and kinetic energy required to penetrate the isolated heads of calves, adult beef cattle, sheep and red deer with a metal probe the same diameter as the bore of an experimental pistol were determined. Approximately 16 and 127 Joules were required to penetrate the heads of adult sheep and cattle, respectively. Using these data a 10 g projectile, consisting of 49 lead pellets and a lead disc in a polyethylene sleeve, was constructed. This projectile, when fired by a charge sufficient to produce a muzzle velocity of 165 m/second, had sufficient kinetic energy to penetrate the heads and brains of cattle, sheep, horses and deer. The projectile was fired from a new design of humane killer with a spring loaded barrel and fitted with a silencer. After penetration of the frontal bones the projectile fragmented and the kinetic energy of its individual particles were insufficient for them to penetrate the opposite side of the head of any of the animals, including one-week-old calves. Fragmentation also caused more brain damage and inhibition of spinal reflexes than a solid free bullet or captive bolt. It is suggested that the use of such a projectile for the emergency slaughter of animals is less hazardous than a solid free bullet and is easier to use and more effective than either a solid free bullet or captive bolt. The projectile was not suitable for killing adult pigs because of problems associated with the frontal sinus.

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.