P. Rodríguez

Assessment of unconsciousness in pigs during exposure to nitrogen and carbon dioxide mixtures

The aim of this study was to assess unconsciousness in pigs during and after the exposure to gas mixtures of 70% nitrogen (N(2)) and 30% carbon dioxide (CO(2)) (70N30C), 80% N(2) and 20% CO(2) (80N20C) and 85% N(2) and 15% CO(2) (85N15C) compared with 90% CO(2) in air (90C) by means of the Index of Consciousness(®)(IoC), their behaviour and the absence of brain stem reflexes. The experiment included three trials of 24 pigs divided into four groups according to the number of treatments. Half of the group was exposed for a short time and the other half for a long time (3 and 5 min for the N(2)/CO(2) mixtures exposure and 2 and 3 min in 90C exposure, respectively). During exposure, the IoC and the electroencephalography suppression rate (ESR) were assessed, as well as the time to onset and percentage of gasping, loss of balance, vocalizations, muscular excitation and gagging. At the end of the exposure, the corneal reflex, rhythmic breathing and sensitivity to pain were each assessed at 10 s intervals for 5 min. Brain activity decreased significantly (P < 0.05) 37.60 s after the start of the exposure to 90% CO(2), which was significantly earlier than in 70N30C, 80N20C and 85N15C exposure, (45.18 s, 46.92 s and 43.27 s, respectively). Before brain activity decreased, all pigs experienced gasping and loss of balance and a 98% muscular excitation. The duration of the muscular excitation was longer in animals exposed to 70N30C, 80N20C and 85N15C than 90C (P < 0.01). After a long exposure time, all animals exposed to 90C died, whereas the 30.4% of animals exposed to N(2)/CO(2) gas mixtures survived. Pigs exposed to 85N15C recovered corneal reflex and sensitivity to pain significantly earlier than when exposed to 90C. Exposure to 90C causes a higher aversive reaction but a quicker loss of consciousness than N(2)/CO(2) gas mixtures. Exposure to N(2)/CO(2) gas mixtures causes a lower percentage of deaths and an earlier recovery of the brain stem activity than 90C, whereas the time to recover the cortical activity is similar. In conclusion, the inhalation of N(2)/CO(2) gas mixtures reduces the aversion compared with high concentrations of CO(2); however, the period of exposure for inducing unconsciousness may be longer in N(2)/CO(2) gas mixtures, and the signs of recovery appear earlier, compared to CO(2).

Aversion to nitrogen and carbon dioxide mixtures for stunning pigs

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.

Aversion to the inhalation of nitrogen and carbon dioxide mixtures compared to high concentrations of carbon dioxide for stunning rabbits

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.

Assessment of unconsciousness during slaughter without stunning in lambs

The aim of this study was to assess brain activity in lambs during slaughter without stunning and its correlation with heart rate (HR) and the absence of physiological reflexes. The index of consciousness (IoC-view®) assesses consciousness by an algorithm that analyses the EEG and gives an index from 0 (unconscious) to 100 (conscious). Eight lambs (Merino breed) of 20 to 25 kg live weight were individually restrained in a stretcher and three skin electrodes were placed at the level of the frontal bone. The electrodes were connected to the IoC-view®. Two additional electrodes were placed on the chest and the HR was transferred to a watch monitor. Recording time started 2 min prior to sticking to attain the basal IoC and HR value of each animal. During bleeding, presence of corneal reflex and rhythmic breathing were recorded every 10 s until brain death. Rhythmic breathing disappeared at an average time of 44 (± 4.2) s after sticking, ranging between 30 and 60 s. The corneal reflex disappeared at 116 (± 11.01) s, ranging between 80 and 160 s after sticking. Changes in the brain activity occurred between 22 to 82 s after sticking (52 [± 20.2] s). In five out of six animals the HR increased (177 [± 22.7] beats min) compared to basal values (139 [± 8.4] beats min) at 115 (± 97.5) s after sticking. Both brain activity and physiological reflexes revealed that when bleeding is performed, through a transverse incision across the neck without stunning, the onset of unconsciousness could last 1 min which impaired animal welfare. This prolonged consciousness compared to other authors’ findings may be attributable to inefficient bleeding when lambs are slaughtered without head restraint.

Assessment of consciousness during propofol anaesthesia in pigs

ANAESTHESIA is required to allow major operative procedures to be undertaken without the animal experiencing pain. In some cases, the assessment of unconsciousness relies on behavioural patterns and physiological reflexes, which need to be validated according to the brain activity. A wide variety of methods have been used to monitorise brain activity in animals (Haga and others 2002, Martin-Cancho and others 2006, Rodriguez and others 2008). However, most of them have been carried out when animals were restrained. The Index of Consciousness (IoC, IoC- view ; Morpheus Medical) is a monitor based on wireless technology that can assess brain activity in non-restraining conditions. The IoC analyses the raw EEG giving a unitless scale from 0 (null brain activity) to 99 (awake) (Revuelta and others 2008). Burst suppression (BS%), which appears when the brain cortex is deeply depressed (Haga and others 2002), is also assessed. The IoC- view monitor is currently used in human beings (Revuelta and others 2008) and has also been used in veterinary medicine to successfully assess the depth of anaesthesia in dogs (Ribeiro and others 2009) and rabbits (Silva and others 2011). Propofol is an injectable anaesthetic agent that can be used both for anaesthetic induction and maintenance (Glen and Hunter 1984, Watkins and others 1987) and has been used in some experiments …