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.

Characterisation of the effect of transport on the welfare of fowl requires common currency methods that can compare the effects of diverse stressors using the same unit of measure. Aversion of broiler chickens (42 ± 1 days old) to vibrational and thermal stressors was investigated in a continuous free-choice procedure. Each choice-chamber had four compartments, connected via a central zone, offering a thermal stressor (T: 40°C, relative humidity 21%), a vibrational stressor (V: 2 Hz, 1 ms−2), concurrent vibrational and thermal stressors (VT), or no applied stressors (N). In experiment 1, there were no significant effects of stressor on the latency to leave the compartments after initial introduction (n = 24). In experiment 2, 12 subjects were introduced individually to a chamber for 4 h during each of a control and two treatment sessions. The results indicated that chickens did not avoid vibration, but significantly avoided the thermal stressor overall (T and VT; P < 0.001). As no interactive effect of the stressors was observed, all avoidance of the combined stressors can be attributed to the effects of the thermal stressor alone. Further work is required to establish ways in which delayed stressors can be studied using behavioural methods before common currency methods can be practicable.

The distress experienced by animals during the induction of unconsciousness remains one of the most important and yet overlooked aspects of effective methods of anaesthesia and euthanasia. Here we show that considerable differences exist in the aversive responses elicited by 12 common methods of inhalational anaesthesia and euthanasia in laboratory rats and mice. Carbon dioxide, either alone or in combination with oxygen or argon, was found to be highly aversive to both species. The least aversive agents were halothane in rats and enflurane in mice. Exposing these animals to carbon dioxide in any form, either for anaesthesia or for euthanasia, is likely to cause considerable pain and distress and is therefore unacceptable when efficient and more humane alternatives are readily available.

In the test described here, sheep are exposed to a situation of conflict between the motivation to approach other sheep and the motivation to avoid a human handler. The distance that the test sheep keep from the handler is a reflection of the relative aversiveness of this handler to the sheep. The test itself requires only a minimum amount of handling and gives the test animals the opportunity to choose their distance from the aversive stimulus, thereby reducing stress during the test itself. The two aversive stimuli chosen for comparison were a human handler facing toward the test arena (more aversive) or the same handler turning his back to the arena (less aversive). Ten Scottish Blackface sheep were tested individually a total of ten times, five times with each of the two stimuli in alternate tests. During the first two tests, nine of the sheep stayed further away when the human was facing toward the arena, compared to when he was facing away; this shows that the test is able to discriminate differences in aversiveness between two stimuli as perceived by individual sheep. This difference was not apparent in the following eight tests, probably because of the fact that the stimuli were not reinforced during the tests. Because the test is concerned with sheep's reaction to a stimulus (eg handler), the procedure associated with the stimulus itself (eg shearing, castration) does not have to be repeated in the test, which means that this method is ideal for studying procedures which cause distress to the animals or which are difficult to repeat.

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.

High concentrations of carbon dioxide (CO2), used for killing laboratory rodents, are known to be more strongly aversive to rats than sweet food items are attractive. This study investigated whether the maintenance of a high oxygen (O2) concentration, using a gas mixture of 70% CO2 and 30% O2, would reduce aversion to CO2 during a gradual-fill procedure. Eight male Wistar rats, aged 10 months, were housed individually in an apparatus consisting of two cages, one higher than the other and joined by a tube. In a series of trials, subjects entered the lower cage for a reward of 20 sweet food items. The gas was turned on at the moment the rat started eating the reward items and flowed into the lower cage at a fixed rate. There were four treatments: 1) 100% CO2 at 14.5% cage volume min–1; 2) gas mixture at 14.5% min–1; 3) gas mixture at 21.0% min–1, which delivered CO2 at approximately 14.5% min–1 and 4) air, with each subject tested with each treatment four times. Measures of willingness to stay and eat in the lower cage (latency to stop eating, latency to leave and the number of reward items eaten) were much lower in all three gas treatments than in air, indicating that the CO2 and the CO2 + O2 mixture were both more strongly aversive than sweet food items were attractive. Comparing the gas mixture with 100% CO2, the latency to leave and the number of reward items eaten were slightly higher in the CO2 + O2 mixture at 21% min–1 than in CO2 at 14.5% min–1, indicating that the addition of O2 slightly reduced the aversiveness of CO2 in the gradual-fill procedure. This reduction is not enough to warrant recommending the use of CO2 + O2 mixtures for killing rats.

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 aim of this study was to assess unconsciousness in pigs during exposure to CO2 through changes in the middle latency auditory evoke 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 [HCO−3]), behaviour and the corneal reflex. The MLEAP did not decrease significantly until after 60 s exposure to CO2. The blood parameters (decreased pH, pO2 and SatO2 and increased pCO2 and HCO3) changed 53 s after the onset of immersion. The burst suppression index (BS%) and the A-line ARX index (AAI) from the MLEAP recovered basal levels at 136 and 249 s, respectively. The first blood parameter to return to basal levels was HCO−3 at 76 s of exposure, followed by SatO2 at 180 s, pH and pO2 at 210 s and pCO2 at 240 s. During exposure to the gas, pigs exhibited lateral head movements and sneezing (10.3 s), gasping (23.5 s) and vocalisation (26.1 s). Furthermore, all pigs demonstrated muscular excitation after between 19 and 39 s exposure, when the AAI and BS% values were not significantly different from basal values. It was suggested, therefore, that these excitatory movements represent conscious movement, indicative of aversion to the gas. According to our results, loss of consciousness began, on average, after 60 s inhalation of 90% CO2. During exposure to the gas, decreased brain activity was seen, immediately following the changes in blood parameters. Following exposure, the restoration of blood parameters to basal levels allows a return to normal brain activity.

In the event of a notifiable disease outbreak, poultry may need to be culled in situ. This should be performed swiftly and humanely to prevent further spread of the pathogen while preserving the welfare of the animals prior to death. Here, we examined the aversion of broiler chicks (Gallus domesticus) to three lethal gas mixtures at various concentrations to determine the least aversive mix that could be used in whole-house gassing. For 1 h, individual chicks (n = 36) were allowed to place their heads inside three feeding and drinking stations (FDS) in order to access food and water. Each FDS was filled with a different gas mixture, and birds could access each FDS as much as they liked. Twelve chicks each were tested at low (50% carbon dioxide [CO2] in air, 70% argon [Ar] in CO2, 70% nitrogen [N2] in CO2), medium (55% CO2 in air, 80% Ar in CO2, 80% N2 in CO2) or high (60% CO2 in air, 90% Ar in CO2, 90% N2 in CO2) concentrations of gas mixtures. Aversion was assessed based on the time birds spent with head in each FDS (with more time indicating less aversive), and the frequency of head shakes relative to time spent with head in the FDS (with a lower proportion indicating less aversive). Data were analysed by ANOVA. On average, birds spent < 3 min with their head in any FDS. Mixtures containing 90% Ar or N2 in CO2 and 80% argon in CO2 were least aversive and mixtures containing 70% N2 in CO2 and 60% CO2 in air were most aversive, based on time spent with head in. Head shakes s−1 were more frequent with low concentration gas mixtures compared to high concentrations, and with all CO2 in air mixtures, which suggests that the intensity of head shaking is related to the concentrations of CO2. From these results, one concentration of each of the three gas mixtures (90% N2 in CO2, 80% Ar in CO2, and 50% CO2 in air) were chosen for assessment on a further 12 birds and the results showed that both inert gas mixtures were less aversive than 50% CO2 in air based on time spent with head in. Frequency of head shakes s−1 did not differ between the three mixtures. Birds found all gases aversive, however it is concluded that inert gas in CO2 mixtures were least aversive compared to CO2 in air and these gases also caused less signs of respiratory discomfort.

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.

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.

The objective of this study was to assess the aversion to exposure of 90% argon, 70% N2/30% CO2 and 85% N2/15% CO2 by volume in atmospheric air in 24 halothane-free slaughter-weight pigs using aversion learning techniques and behavioural studies in an experimental slaughterhouse. Pigs were subjected to the treatments individually during 2 separate trials of 12 animals each. The time of exposure to the gases was 46 and 32 s, respectively. When the pit contained any of the 3 gas mixtures, the time taken to cross the raceway and enter the cradle (TCREC) increased compared with the training sessions (atmospheric air). The incidence of pigs showing retreat and escape attempts and gasps and the number of times that this behaviour was performed was lower in 90% argon than in the gas mixtures with N2 and CO2. On the other hand, the time to loss of posture was lower with 70% N2/30% CO2 than with argon. The second exposure to all gas mixtures was more aversive than the first and the loss of posture also occurred earlier in the second exposure. In conclusion, pigs showed more aversion to gas mixtures with N2 and either 15% or 30% CO2 by volume than 90% argon by volume.

Stunning by inhalation of nitrogen (N2) and carbon dioxide (CO2) mixtures reduces aversion compared to high concentrations of CO2 in pigs and poultry. The objective of the study was to assess the aversion to 90% of CO2 (90C) and an alternative gas mixture of 80% N2 and 20% CO2 (80N20C) in commercial rabbits (Oryctolagus cuniculus). Sixty animals, divided into two groups, were used. During the first day, the rabbits of both groups were lowered in pairs into the pit with atmospheric air and their behaviour was recorded as control. During the second day, one group was exposed, again in pairs, to 90C and the other to 80N20C for 1 min. Exploratory behaviour and general activity were assessed 2 min before the exposure, during the exposure and for 2 min subsequently. During the exposure, signs of respiratory distress, loss of balance, muscle twitching and recovery of balance were also assessed. In the control sessions (atmospheric air), animals did not show respiratory distress or muscle twitching and were less active while the crate was descending than when gas treatments were applied. The percentage of animals with respiratory distress was higher in 90C (97%) than 80N20C (40%). Muscle twitching occurred earlier in 80N20C (97%; 23.9 s) than in 90C (17%; 37.4 s). A second phase of muscle twitching occurred only in 90C at 93.0 s. Mean latency of lost of balance and recovery were lower in 80N20C (24.2 and 98.6 s, respectively) than in 90C (28.2 and 110.2 s, respectively). It is concluded that rabbits showed less signs of respiratory distress to inhalation of 80N20C than 90C but more signs of aversion than when they were exposed to atmospheric air.

The well-replicated observation that many people maintain mental health despite exposure to severe psychological or physical adversity has ignited interest in the mechanisms that protect against stress-related mental illness. Focusing on resilience rather than pathophysiology in many ways represents a paradigm shift in clinical-psychological and psychiatric research that has great potential for the development of new prevention and treatment strategies. More recently, research into resilience also arrived in the neurobiological community, posing nontrivial questions about ecological validity and translatability. Drawing on concepts and findings from transdiagnostic psychiatry, emotion research, and behavioral and cognitive neuroscience, we propose a unified theoretical framework for the neuroscientific study of general resilience mechanisms. The framework is applicable to both animal and human research and supports the design and interpretation of translational studies. The theory emphasizes the causal role of stimulus appraisal (evaluation) processes in the generation of emotional responses, including responses to potential stressors. On this basis, it posits that a positive (non-negative) appraisal style is the key mechanism that protects against the detrimental effects of stress and mediates the effects of other known resilience factors. Appraisal style is shaped by three classes of cognitive processes – positive situation classification, reappraisal, and interference inhibition – that can be investigated at the neural level. Prospects for the future development of resilience research are discussed.

The aim of this study was to assess the effect of exposure to the gas mixtures of 70% nitrogen (N2) and 30% carbon dioxide (CO2; 70N30C), 80% N2 and 20% CO2 (80N20C) and 85% N2 and 15% CO2 (85N15C) on aversion, stunning effectiveness and carcass, as well as meat quality in pigs, and to compare them with the commercial stunning of 90% CO2 (90C). A total of 68 female pigs were divided into four groups and stunned with one of the gas mixtures. During the exposure to the gas, behavioural variables (retreat attempts, escape attempts, gasping, loss of balance, muscular excitation and vocalizations) were recorded, and at the end of the stunning, corneal reflex and rhythmic breathing were assessed. After slaughter, meat quality parameters such as pH at 45 min post mortem (pH45) and at 24 h post mortem (pHu), electrical conductivity, drip loss and colour, in the Longissimus thoracis (LT) and Semimembranosus (SM) muscles were measured, and the presence of ecchymosis on the hams was noted. The PROC MIXED and the PROC GENMOD of SAS® were used to analyse the parametric and binomial variables, respectively. The ‘gas mixture’ was always considered a fixed effect and the ‘live weight’ as a covariate. To assess the correlation between meat quality and behaviour measures, PROC CORR was used. Pigs exposed to 90C showed a higher percentage of escape attempts and gasping, a lower percentage of vocalization and shorter muscular excitation phase than pigs exposed to the other N2 and CO2 mixtures (P < 0.05). After stunning, no pig exposed to 90C showed corneal reflex or rhythmic breathing, whereas 85% and 92% of the animals exposed to N2 and CO2 mixtures showed corneal reflex and rhythmic breathing, respectively. Animals stunned with 80N20C and 85N15C had a lower pH45 (P < 0.01) than animals exposed to 90C. Electrical conductivity in the SM muscle was lower (P < 0.001) in 90C and 70N30C pigs than in 80N20C and 85N15C pigs, whereas in LT, it was lower (P < 0.05) in 90C pigs than in 85N15C. As the CO2 concentration of the gas mixture was decreased, the prevalence of exudative pork increased. Twenty-five percent of animals exposed to N2 and CO2 mixtures (n = 68) had ecchymosis in their carcasses, whereas no animal stunned with 90C had ecchymosis. In conclusion, although N2 and CO2 stunning exhibit fewer signs of aversion than 90C, their induction time to unconsciousness is longer, and this may negatively affect meat and carcass quality.