Aversion to the dip-lift stunning system and to the inhalation of 70 and 90% carbon dioxide was assessed in 18 halothane-free (NN) and 14 heterozygous halothane (Nn) slaughter weight pigs using aversion learning techniques and behavioural studies in an experimental slaughterhouse. Pigs were subjected to the treatments individually. When the dip lift system contained atmospheric air, the proportion of pigs that entered the crate voluntarily increased on subsequent days, indicating that pigs habituate to the stunning system. Based on the number of attempted retreats, for the first descent into the well with atmospheric air, Nn pigs were more reactive than NN pigs. On repeating the descent, Nn pigs showed greater habituation to the procedure. When the pit contained (either 70 or 90%) carbon dioxide, the time taken to enter the crate and the incidence of pigs that attempted to retreat increased on subsequent days, indicating aversion to the carbon dioxide concentrations. The aversion was higher when the stunning system contained 90 as opposed to 70% carbon dioxide due possibly to increased irritation of the nasal mucosal membranes and more severe hyperventilation. Conversely, a decrease in the concentration of carbon dioxide increased the time to loss of posture and, therefore, lengthened the perception of the aversive stimulus till the animal lost consciousness. These results suggest that stunning with carbon dioxide is not free from pain or distress. The degree of aversion depends on the carbon dioxide concentration. Therefore, if higher concentrations of carbon dioxide are recommended for rapid induction of anaesthesia, it needs to be assumed that this may be more aversive to pigs.

The return to consciousness of 24 electrically stunned lambs was assessed by measurement of physiological reflexes and electroencephalography (EEG) recordings. The physical activity of the lambs after head-only electrical stunning included one tonic phase and two clonic phases. The tonic phase began immediately after the stun and ended 10 s after the stun; the first clonic phase started immediately after the tonic phase and ended 36 s after the stun, and the second clonic phase started immediately after the first clonic phase and ended 70 s after the stun. During the tonic phase and the first clonic phase, electrical activity recordings of the brain showed a dramatic increase in the relative power spectra of alpha and beta frequencies. Both frequencies returned to pre-stun levels with the end of the first clonic phase. During the second clonic phase, the relative power spectrum of theta frequency was higher than that before stunning. These results suggest that during the tonic phase and the first clonic phase, the animal was unconscious, whereas during the second clonic phase the return of some conscious function began. Spontaneous breathing returned at about 29 s post-stun, whereas the corneal reflex returned at about 38 s. It is therefore suggested that the return of spontaneous breathing is the safest indicator that the animal is close to recovering consciousness.

The effectiveness of head-only electrical stunning of broilers, with a root mean square (RMS) current of 100 or 150mA delivered using either 50, 400 or 1500Hz sine wave alternating current (AC), was investigated. The changes occurring in the spontaneous electroencephalogram (EEG) were evaluated using Fast Fourier Transformations (FFT) to determine the impact of the amount and frequency of stunning current on total (2-30 Hz) and relative (13-30 Hz) power contents in the EEG. Induction of epileptiform activity and reduction in the EEG power contents to less than 10% of pre-stun levels from the end of epileptiform activity were used as indicators of effective stunning. The duration of unconsciousness and insensibility was determined on the basis of the return of EEG power contents. In addition, the changes occurring in somatosensory evoked potentials (SEPs) were subjectively evaluated to determine the impact of stunning treatments. The results of ANOVA (repeated measures) showed statistically significant effects of interactions between the current frequencies, amount of current and repeated measures on changes in EEG power contents (P < 0.001). Stunning broilers with 150 mA delivered using 50 Hz resulted in EEG changes that were indicative of more pronounced neuronal inhibition following epileptiform activity and also lasted longer than was the case when broilers were stunned with 150 mA delivered using 400 Hz. Stunning broilers with 100 mA delivered using 50 Hz resulted in changes very similar to those observed after stunning with 150 mA of 50 Hz, but which lasted for a relatively shorter time. However, these changes were more pronounced and lasted longer than did stunning with 100 mA delivered using 400 Hz. The effects of stunning broilers with 150 mA of 400 Hz were similar to those found after stunning with 100 mA of 50 Hz. By contrast, stunning broilers with 100 mA of 1500 Hz failed to fulfil the criteria set out in this study. Stunning of broilers with 150 mA of 1500 Hz induced epileptiform activity but failed to reduce EEG power contents to less than 10% of pre-stun levels. Therefore, the stunning of broilers with 100 or 150 mA of 1500 Hz may not be adequate to avoid pain and suffering during slaughter. Thus, minimum currents of 100, 150 and 200 mA should be delivered whilst using 50, 400 and 1500 Hz, respectively, to achieve effective electrical stunning in broilers. Severing of the carotid arteries in the neck following head-only electrical stunning, and high frequency (> 125 Hz) electrical water bath stunning of broilers should also become a statutory requirement to prevent the return of consciousness during bleeding.

Proper design of restraint equipment is essential to prevent stress on animals during handling, stunning and slaughter. A small design mistake which may appear to be insignificant to the engineer can be extremely detrimental to animal welfare. Operators of restraint equipment must be properly trained. Cattle will place their heads into stanchion (yoke) or chin-lift types of head-restrainers if they are gently moved forward by a rear pusher gate. Cattle confined in an upright ASPCA pen for religious slaughter will remain calmer if the apparatus is gently closed around them. The vertical travel of the belly lift should be restricted to 71 cm (28 in) — it should not lift the animals off the floor. The rear pusher gates should be equipped with a separate regulator to prevent excessive pressure from being applied. Stunning or ritual slaughter should be carried out within 10 seconds of the animal's head being restrained. The modified ASPCA pen described in the paper was seemingly humane when operated by people concerned about animal welfare.

The severity of respiratory distress occurring prior to loss of posture during exposure to: 20, 30, 40, 50, 60, 70, 80 or 90 per cent carbon dioxide in air; 2 or 5 per cent residual oxygen in argon; 30 per cent carbon dioxide in argon with either 2 or 5 per cent residual oxygen; or 40 per cent carbon dioxide in argon with either 2 or 5 per cent residual oxygen, was subjectively determined in pigs from their behaviour. The results indicated that exposure to 2 per cent oxygen in argon (anoxia) induced minimal respiratory distress, 30 per cent carbon dioxide in argon with 2 per cent residual oxygen induced a moderate distress and exposure to all the concentrations of carbon dioxide in air induced severe respiratory distress in the pigs. From the animal welfare point of view, using 2 per cent oxygen in argon (anoxia) appears to be the optimum choice for gas stunning pigs. Secondly, a mixture of 30 per cent carbon dioxide in argon with 2 per cent residual oxygen is preferred to 90 per cent carbon dioxide in air.

The behavioural reactions and blood Cortisol levels of cattle stunned using a penetrating captive-bolt pistol whilst standing free in a stunning box were compared with those obtained from cattle similarly stunned but with their heads held in a hydraulically operated chin-lift type of head restrainer. Few (8 out of 55) animals voluntarily put their heads into the restrainer, most had to be ‘persuaded’ to use the head-restrainer; some (5 out of 24) could not be. The mean time between entry into the stunning pen and the stun for 23 free standing animals was 5.6s and for 19 animals which could be persuaded to use the head restrainer was 34.2s. The Cortisol levels in the blood taken at the stick, from 30 animals stunned while standing free was 67.6 nmoVlitre while that from 30 stunned while head-restrained was 143.1 nmolHitre. The behaviour and Cortisol results suggest that enforced usage of this type of head restrainer could be a cause of distress to the cattle involved.

UK legislation requiring pre-slaughter stunning has certain exemptions for religious slaughter. Supporters of both Muslim (Halal) and Jewish (Shechita) slaughter methods claim that the efficiency of the bleed out is adversely affected by stunning. In this study, electrical stunning followed by neck cutting, and captive bolt stunning followed by neck cutting, were compared with the Muslim slaughter method (neck cutting without stunning) in sheep. Total blood loss and percentage blood loss, expressed as a percentage of live weight, were calculated and compared between groups. In addition, the time taken to reach 25%, 50%, 75% and 90% of total blood loss was calculated and compared. There was no apparent difference in the packed cell volume levels between groups. Slaughter method did, however, affect meat pH and colour. The results show that the bleed out after neck cutting is not adversely affected by electrical or captive bolt stunning; nor is an improved bleed out achieved by neck cutting without stunning.

The aversive effects of 90 per cent argon in air, 30 per cent carbon dioxide in air or 90 per cent carbon dioxide in air were investigated in slaughter weight pigs. Aversion was assessed from their reluctance to enter the three gaseous atmospheres to obtain a reward (apples). The pigs did not show any aversion to the inhalation of 90 per cent argon in air. The majority of the pigs did not show aversion to the presence of 30 per cent carbon dioxide in air. By contrast, the inhalation of 90 per cent carbon dioxide was aversive to the majority of the pigs. Fasting them for up to 24h prior to testing did not overcome the pigs ‘ reluctance to enter an atmosphere containing 90 per cent carbon dioxide.

The objective was to evaluate the welfare implications of electrical stunning prior to gill-cutting of farmed African catfish as an alternative to live chilling in combination with gutting. Electroencephalogram (EEG) and electrocardiogram (ECG) recordings, in combination with observation of behaviour and responses to noxious stimuli, were used to assess brain and cardiac function in African catfish (body-weight 1571 ± 362 g [mean ± standard deviation], 32 males and 26 females). In the first experiment, the minimum electrical current required to induce a general epileptiform insult by head-only stunning was determined. The individual catfish were fixed in a specially designed restrainer, and applied voltages of 150 V, 200 V, 250 V, 300 V or 350 V (50 Hz AC) were delivered via scissor-model stunning tongs for approximately I s. A general epileptiform insult was observed in 31 fish, for which a successful EEG recording was obtained using 362 ± 32 V, 629 ± 180 mA for 1.2 s. The durations of the tonic, the clonic and the exhaustion phases were 8 ± 3 s, 12 ± 7 s and 7 ± 5 s as measured by EEG, respectively; a distinct exhaustion phase was not clear in II fish. The total duration of the insult was 23 ± 8 s. After the insult the fish recovered. The heart rate was 63 ± 29 beats min I prior to stunning. After stunning, the ECG revealed extrasystole and was irregular. By using an average current of 629 ± 180 mA (at approximately 360 V, 50 Hz AC), at least 91% of fish are effectively stunned with a confidence level of 95%. In the second experiment, the behaviour of 10 individual catfish, which were able to move freely in water, was observed following head-only stunning (370 V). The durations of the tonic, clonic and exhaustion phases in free-swimming fish were II ± 8 s, 20 ± 5 s and 23 ± 20 s, respectively. All fish recovered. In the third experiment, a group of seven catfish was head-only stunned followed by gill-cutting to kill them as a second procedure (ie after recovery from head-only stunning). No brain activity was seen on the EEG 12 ± 5 s after stunning. However, two fish showed responses to noxious stimuli after 2 min and 5 min. A second group of seven catfish was gill-cut only. They responded to noxious stimuli for at least 15 min. The blood loss was 1.2% and I.0% of live weight for the first and second group, respectively. It may be concluded from our results that African catfish are effectively stunned for 23 ± 8 s with a current of 629 ± 180 mA for 1.2 s, after which they recover. Since evoked responses may remain for at least 5 min after stunning and gill-cutting, we recommended that the stunning and killing procedure should be optimised.

Some supporters of religious slaughter methods claim that efficiency of bleed-out is adversely affected by stunning. Our previous study carried out in sheep at an abattoir comparing the Muslim method of slaughter without stunning with pre-slaughter stunning using a captive bolt or by electrical methods concluded that bleed-out is not adversely affected by stunning, nor improved by a neck cut without stunning. In this paper, a similar study carried out in cattle is reported. In this study, captive bolt stunning followed by neck cutting was compared with the Muslim slaughter method without stunning. The total blood loss, percentage blood loss expressed as a percentage of live weight and percentage loss of estimated total blood were calculated and compared between each group. In addition, the time periods taken to reach 25, 50, 75 and 90% of total blood loss were also calculated. There was no significant difference between the two stunning groups for any of these blood loss variables. The results, subjected to statistical analyses, also showed no apparent difference in the PCV levels and meat quality parameters between treatments. These results confirm the findings with sheep and show that the bleed-out is not adversely affected by captive bolt stunning, nor improved by a neck cut without stunning in cattle. It is anticipated that these findings may help promote the use of stunning methods during Halal slaughter.

Despite recent technological advances, stunning efficiency of broilers in commercial plants is still questionable and a major public concern. The aim of this survey was to assess the electric water-bath parameters used in poultry processing plants, establish practical ways for the assessment of stunning efficiency in these conditions, link their incidence to the applied current and propose methodology for the online evaluation of the effectiveness of electrical water-bath stunning. A total of 5,378 broilers were assessed randomly for signs of post-stun recovery at 4, 8, 13 and 25 s post-water-bath exit (WBE) through corneal reflex, rhythmic breathing, head shake and escape behaviour on three processing lines. The electric water-bath parameters used did not meet the recommended current and frequencies for effective stunning. No rhythmic breathing was detected with any of the birds at 4 s post water-bath exit, while this reflex returned by 8 s in some birds. Broilers that had their necks cut had a significantly lower incidence of breathing compared to those that missed the neck cutter. The electric water-bath stunners that were tested did not abolish the corneal reflex where 38.4% of birds tested positive, at 4 s post WBE. Pulsed DC-stunned birds that missed the knife had a significantly higher incidence of positive corneal reflexes than those that had their necks cut. Head shake was present on 26.7% of the birds when assessed at 25-30 s post WBE. The trends in incidence of behavioural reflexes with time post WBE may be used for the assessment of stunning efficiency, particularly on birds that miss the knife, but none of the assessed indicators could unequivocally demonstrate unconsciousness.

There have been many improvements regarding transport conditions, pre-slaughter handling, and captive-bolt stunning of cattle at commercial abattoirs, but many challenges still exist. Animals unaccustomed to human-animal contact, such as free-range beef cattle, may be especially difficult to handle on the day of slaughter. Shifting of the slaughter process from the abattoir to the animals’ familiar environment could improve animal welfare at slaughter. In 2011, the German government passed an amendment allowing farmers to slaughter free-range cattle, on-farm, using a rifle. A proper stun is vital when employing this method but neither sufficient practical experience nor scientific knowledge are in place to allow this. Thus, this study aimed to examine shot placement and the effect of diverse ammunition by means of shooting at cattle heads, post mortem, with a rifle. Impact was assessed using brain tissue damage observed from skull dissections. Placing the shot frontally at the forehead resulted in severe brain damage significantly more frequently than targeting laterally. A precise frontal shot, utilising both large and small bore calibres, caused severe brain damage that would almost certainly have led to immediate unconsciousness and death. One of the small bore calibres caused minimal brain damage apart from the trajectory. However, this was the only calibre not passing straight through. Due to the fact that the bullet remains within the skull, thus transferring all of its energy to the skull and brain, the impact of this calibre on the brain would also be expected to be rapidly fatal. A projectile that does not exit the skull would also be advantageous as regards safety.

The killing of animals is the subject of societal and political debate. Wild geese are caught and killed on a regular basis for fauna conservation and damage control. Killing geese with carbon dioxide (CO2) is commonly practiced, but not listed in legislation on the protection of flora and fauna, and societal concerns have been raised against this method. In this study, an experiment was carried out killing 30 wild-caught geese using either CO2 or a mixture of CO2 and argon (Ar). Brain function (EEG) and heart function (ECG) were measured to determine loss of consciousness and onset of death. The stage of unconsciousness was reached on average within one minute in both treatments (56 s for CO2 and 50 s for CO2 and Ar). States of minimal brain activity and ineffective heart beat were reached more quickly using CO2 compared to CO2 and Ar (112 versus 178 s for minimal brain activity and 312 versus 394 s for ineffective heart beat for CO2 and the mixture of CO2 and Ar, respectively). The mixture of carbon dioxide and argon did not significantly reduce time to loss of consciousness or death. Further studies on behaviour and stress physiology are needed to determine conclusively whether CO2 alone is a satisfactory agent to kill wild-caught geese as the lower CO2 concentration in the CO2-Ar treatment may act as a sedative and reduce the aversiveness of the animals during exposure to lethal gas concentrations.

The slaughter of animals for the halal market is both ethically and economically significant. There are animal welfare and spiritual requirements that must be met for meat to be considered fit for Muslim consumption. These requirements are enshrined in Islamic law, known commonly as the Shariah law, derived from commandments in the Holy Quran and the Hadith (teachings or traditions of the Prophet of Islam, Mohammed, Peace Be Upon Him). Islamic jurists widely interpret the Shariah law differently, and this has led to debate as to whether pre-slaughter stunning is acceptable for halal slaughter. This paper reviews how these laws are interpreted and implemented and reviews the methods of stunning accepted by proponents of halal stunning. It also describes why some proponents of halal stunning do not accept irreversible stunning methods for producing halal beef within the EU, a situation which has meant that thousands of halal cattle are slaughtered without any form of stunning.

Slaughter is considered an important fish welfare issue. For a slaughter method to be considered humane, effective stunning that lasts until death as well as the reduction of pain and fear throughout all procedures are essential. Our objective was to investigate current techniques for slaughtering fish in Brazil. A digital questionnaire with six multiple-choice and three open questions was distributed to companies registered as fish slaughterhouses and to fish farms in 2019, addressing fish species, quantities processed and slaughter procedures adopted. From 62 facilities in 15 Brazilian states that answered the survey, nine slaughterhouses and 30 fish farms slaughtered fish, totalling 452 tonnes per day. All reported pre-slaughter stunning, and live chilling to be the most commonly cited method (82.0%), followed by electronarcosis (18.0%). Slaughtering techniques included exsanguination (38.5%) and decapitation (2.5%). For the remaining companies, no slaughter method was declared, suggesting death by asphyxiation or by further processing (59.0%). Twenty-nine companies adopted pre-slaughter fasting, lasting from 10 to 48 h. All sites worked with tilapia (100%) and 24 (82.7%) reported that they worked exclusively with this species. Other species reported were: pacu (25.6%), tambacu (17.9%), tambaqui and carp (15.3%), jundiá (12.8%), pintado and pirarucu (7.7%), matrinxã and pangassius (5.1%). Asphyxia and live chilling are not considered humane, as animals remain conscious and, thus, suffer. Results show that most establishments do not perform humane slaughter. This scenario highlights the urgent need for development and enforcement of humane fish slaughter techniques, with routine supervision and normative requirements.

The stability and uniformity of the following gas mixtures: 90% argon; 85% argon and 15% carbon dioxide (CO2); 70% argon and 30% CO2; 98% nitrogen (N2); 92% N2 and 8% CO2; 90% N2 and 10% CO2; 85% N2 and 15% CO2; 80% N2 and 20% CO2; 70% N2 and 30% CO2; and 90% CO2 by volume in atmospheric air were assessed in a commercial dip-lift stunning system when the cradle was either stationary or in motion. The gas mixtures of 90% argon, 85% argon and 15% CO2, 70% argon and 30% CO2, 85% N2 and 15% CO2, 80% N2 and 20% CO2, 70% N2 and 30% CO2 and 90% CO2 by volume in atmospheric air could be sustained in a commercial dip-lift stunning system. The stability of the gas mixtures 92% N2 and 8% CO2, and 90% N2 and 10% CO2 by volume in atmospheric air were lower than in the previous cases. On the other hand, an N2 concentration higher than 94% by volume in atmospheric air could not be sustained in the stunning system. In addition, gas mixtures of argon and CO2 showed a higher stability than gas mixtures of N2 and CO2. The uniformity at different levels inside the pit (defined as the capacity of the gas to maintain its concentration constant at different levels inside the pit) was higher in 90% argon, or argon and CO2 mixtures and N2 and CO2 mixtures than in 90% CO2. This fact ensures that for the whole time the animals are inside the pit, the same conditions are applied, which is not the case for 90% CO2.

Inhalation of concentrations greater than 30% of carbon dioxide (CO2) by volume in atmospheric air causes aversion in pigs. The objective of this study was to assess, using aversion learning techniques and behavioural studies, the aversion to three alternative gas mixtures of nitrogen (N2) and CO2: 70% N2 and 30% CO2 (70N30C), 80% N2 and 20% CO2 (80N20C) and 85% N2 and 15% CO2 (85N15C). The experiment consisted of two trials of three groups of ten pigs each. Pigs were placed individually at the starting point of the test facility and allowed to enter the crate of a dip-lift stunning system during one control session with atmospheric air and three treatment sessions with one of the gas treatments in each group. When the pit contained any of the three gas mixtures, the time taken to cross the raceway and enter the crate did not increase compared to the control session. However, when exposed to the gas mixtures, the majority (85.80%) of pigs performed attempted retreats in the crate, 22.22% exhibited escape attempts, and 7.91% vocalised, without differences between gas mixtures. The percentage of pigs gasping was higher when exposed to 70N30C compared to 80N20C and 85N15C. The results suggest that pigs show signs of aversion to the inhalation of 15 to 30% CO2 in nitrogen atmosphere compared to atmospheric air but the aversion response did not increase in consecutive sessions.

During the commercial slaughter of farmed turbot (Scophthalmus maximus), a total of 67 fish were, on six occasions, removed from their rearing conditions at 14°C and put, as is standard commercial practice, into chilled seawater (-1.5 to -0.8°C) to monitor behavioural, muscular, osmoregulatory and respiratory responses during chilling time (90 min). Results show that a thermal insult alters the iso-osmotic balance, leading not only to an Na+ influx and an intracellular release of Ca2+ and K+, but also to a disturbance of respiratory function, leading to acidosis as a result of H+ and CO2 accumulation, increased pCO2 and reduced HCO3− in the blood. Once the internal temperature dropped below 1°C, the muscles contracted (cold shortening) and, although the fish were still alive, they reverted to a state of rigor, leading to a complete breakdown in their ability to move or ventilate and resembling an unconscious condition or death. Remarkably, the fish were able to prevent themselves undergoing hypoxia as pO2 remained within acceptable limits. No changes in muscle pH were observed and, thus, no noted effects on textural properties. We conclude that live chilling from 14°C to approximately -1°C is a highly questionable practice. It causes physical and physiological changes that are generally associated with stress and, in the case of observed forced muscle contractions, could lead to severe pain. Furthermore, we conclude that cold shortening associated with chilling can be easily mistaken for rigor mortis and, as such, should be subject to further attention in future research on quality.

The most widely used stunning method in sheep is electrical. However, in lambs, this method leads to rupture of the blood vessels, provoking ecchymoses. In pigs (Sus scrofa), the use of CO2-stunning systems has increased in popularity due to positive effects on meat quality and animal welfare (movement of animals in groups). The aim here was to assess the effectiveness of a progressive exposure to 90% carbon dioxide (CO2) in inducing unconsciousness in lambs (Ovis aries) through changes in the middle latency auditory-evoked potentials (MLAEP) of the central nervous system (CNS), blood parameters (pH, carbon dioxide partial pressure (pCO2), oxygen partial pressure (pO2), oxygen saturation (SatO2) and bicarbonate (HCO3J, behaviour (head-shaking, sneezing, gasping and gagging) and physiological reflexes (corneal reflex, breathing and sensitivity to pain). Fourteen male lambs of the Ripollesa breed, weighing between 19 and 25 kg were progressively exposed to an atmosphere of 90% CO2 over 66 s. All blood parameters changed between 23 and 43 s after the onset of the immersion. The MLAEP did not decrease significantly until after 48 s exposure to CO2, suggesting an absence of auditory-evoked brain activity. Before that, lambs exhibited head-shaking and sneezing starting at 10.6 (± 0.77) s, and gasping starting at 20.6 (± 1.36) s. After exposure, all animals showed absence of breathing and sensibility to pain, and 36% of them absence of corneal reflex. The pH and pCO2 recovered basal values at 90 and 120 s, respectively, after the end of the exposure. The burst suppression index (BS%) and the A-Line ARX index (AAI) recovered basal levels at 116 and 159 s, respectively. Exposure to CO2 at high concentration induces effective stunning in sheep for a period of 124 s. However, during exposure, the animals exhibited signs of aversion and breathlessness.