S.B. Wotton

Changes in the somatosensory evoked potentials and spontaneous electroencephalogram of broiler chickens during exposure to gas mixtures.

1. Six week-old broiler chickens implanted with electroencephalogram (EEG) recording and somatosensory stimulating electrodes were exposed to either 90% argon in air, a mixture of 30% carbon dioxide and 60% argon in air or a mixture of 30% oxygen and 40% carbon dioxide (balance nitrogen) for 2 min, to determine the times to onset of changes in spontaneous EEG and the loss of somatosensory evoked potentials (SEPs) and thus unequivocal loss of consciousness. 2. In addition, after a 2 min exposure to the carbon dioxide-oxygen mixture, some broilers were allowed to recover in air and their EEGs and SEPs were continuously recorded until the return of normal EEG and SEPs. During this period, the time to return of response to comb pinching was also determined in 10 broilers. 3. All broilers exposed to either argon or the carbon dioxide-argon mixture died within 2 min, whereas, only 3 out of 17 broilers died during the 2 min exposure to the carbon dioxide-oxygen mixture. 4. During exposure to argon, unlike the other 2 gas mixtures, the majority of broilers showed high amplitude, low frequency electrical activity in the EEG on average at 10 s. The mean times to onset of EEG suppression were 17, 19 and 40 s after exposure to argon, the carbon dioxide-argon mixture and the carbon dioxide-oxygen mixture, respectively. An isoelectric EEG occurred on average at 58 and 41 s after exposure to argon and the carbon dioxide-argon mixture, respectively. An isoelectric EEG did not occur in broilers which were exposed to the carbon dioxide-oxygen mixture. 5. The SEPs were abolished in broilers on average 32 and 24 s after exposure to argon and the carbon dioxide-argon mixture, respectively. During exposure of broilers to the carbon dioxide-oxygen mixture the SEPs were abolished in the majority of birds on average at 47 s, however, 2 out of 14 birds retained their SEPs for the entire period of 2 min exposure to this gas mixture. 6. During the recovery after exposure to the carbon dioxide oxygen mixture, response to comb pinching and SEPs returned either at the time of, or soon after, the onset of high frequency electrical activity in the suppressed EEG of broilers. The mean times to return of response to comb pinching and SEPs were 52 and 43 s, respectively. 7. Based on the time to onset of EEG suppression or loss of SEPs, exposure of broilers to either 90% argon in air, or a mixture of 30% carbon dioxide and 60% argon in air, resulted in quicker loss of consciousness than during exposure to a mixture of 40% carbon dioxide, 30% oxygen and 30% nitrogen. The time to return of consciousness after a 2 min exposure to the carbon dioxide-oxygen mixture was also found to be rapid.

Effect of electrical stunning frequency on ventricular fibrillation, downgrading and broken bones in broilers, hens and quails

The effect of stunning current frequency on the incidence of ventricular fibrillation was determined in broilers and hens. When a pulsed unipolar square wave (DC) was used the incidence of ventricular fibrillation decreased as the frequency was increased beyond 125 Hz. When a sinusoidal AC was used, 50 Hz killed some of the birds whereas at the corresponding r.m.s. currents no birds experienced a ventricular fibrillation with 1500 Hz. In quail, it was found that between 45 and 110 mA (50 Hz) all birds experienced a ventricular fibrillation. The effect of 50, 200 and 350 Hz square wave DC on carcass downgrading was examined in broilers, and there were no differences between the groups. It was concluded that there were few advantages from using high frequency stunning currents in poultry.

Effectiveness of electrical stunning applied using a variety of waveform-frequencycombinations and consequences for carcase quality in broiler chickens

1. The effectiveness of electrical stunning of poultry was assessed where the recommended current of 105 mA per bird was applied using a range of waveform-frequency combinations. In addition the effect of the treatments on subsequent carcase quality was investigated. 2. The use of frequencies greater than 50 Hz was associated with a failure to induce ventricular fibrillation. 3. All waveform-frequency combinations were equally effective in producing a stunned state; the time to recovery was not affected by stunning treatment but was significantly longer in heavier birds. 4. The use of high frequency (500 Hz and 1500 Hz) stunning currents resulted in a decrease in carcase downgrading and a marked reduction in the occurrence of breast muscle haemorrhages, which represent significant commercial benefits to be gained by their use.

Electrical stunning of cattle.

Cattle are normally stunned electrically by three sequential cycles, first a three-second head-only cycle, to stun the animal, secondly a 15-second cardiac cycle, to induce ventricular fibrillation (cardiac arrest), and thirdly a four-second discharge cycle, to reduce convulsions after death. An effective and immediate stun was produced when ≥1.15 amps sinusoidal Ac at 50 Hz was applied between the nose and neck electrodes for less than one second. However, when applied for three seconds, head-only currents of >0.46 amp sinusoidal Ac at 50 Hz were sufficient to induce epileptiform activity in the brain, identified as high amplitude low frequency activity in the electroencephalogram. The induction of effective head-only electrical stunning resulted in an average interval of 50 seconds before the return of rhythmic breathing movements, and positive corneal and palpebral reflexes. The cardiac arrest cycle successfully induced ventricular fibrillation when >1.51 amps sinusoidal AC at 50 Hz was applied for five seconds between the nose and brisket electrodes.

Welfare of calves - 2. Increase in vertebral artery blood flow following exsanguination by neck sticking and evaluation of chest sticking as an alternative slaughter method.

The role of the vertebral arteries in delaying loss of sensibility following neck sticking in slaughter calves was investigated. Vertebral artery blood flow was measured using probes before, during and after electrical stunning and slaughter. Systemic blood pressure, electrocorticogram, visually evoked responses and the occurrence of carotid occlusions were also recorded. When carotid occlusion occurred, the time to onset of brain failure was delayed based on the development of an isoelectric state. In addition, when carotid occlusion occurred the mean arterial blood pressure was sustained for longer following slaughter, and concurrently vertebral artery blood flow could be maintained at about 30% of its initial level for up to 3 min. In some animals vertebral artery flow increased substantially following sticking. When chest sticking was used no occlusion of vessels occurred, mean arterial blood pressure fell promptly (within 8 s) and the onset of an isoelectric state did not extend beyond one minute. In addition, visually evoked responses were not present after 5 s following chest sticking.

Carcase and meat quality in broilers either killed with a gas mixture or stunned with an electric current under commercial processing conditions

1. Carcase and meat quality were evaluated under commercial conditions in 400 broilers either killed with a mixture of 30% carbon dioxide and 60% argon in air or stunned with a 50 Hz AC with clipped sine wave. 2. Compared with electrical stunning, killing broilers with the gas mixture eliminated or substantially reduced the prevalence of carcase and meat quality defects. 3. The results also showed that killing broilers with a mixture of 30% carbon dioxide and 60% argon would enable filleting (deboning) to be performed at 4 h post mortem without adversely affecting the cook loss or texture of breast meat.

Transportation of ostriches - a review

The transport of farm animals has been the subject of much research in recent years; however, the information available on ostrich transportation is limited. This paper draws together past and recent scientific literature and practical experience. The current state of knowledge is summarised and areas which require further research are identified.

Effectiveness of different electrical stunning regimens for turkeys and consequences for carcase quality.

This study examined the effectiveness of electrical stunning of turkeys applied at 150 mA per bird utilising a range of waveform-frequency combinations. In addition, the effect of stunning treatment on subsequent carcase quality was examined. The effectiveness of stunning, as judged by time to recovery, was similar regardless of bird weight or applied stunning treatment. Increasing waveform frequency was associated with a decrease in the prevalence of ventricular fibrillation, although turkeys appeared more susceptible than broilers. Use of the higher frequency waveforms (500 and 1500 Hz) was associated with a marked improvement in carcase quality, particularly with regard to breast muscle haemorrhaging and their use may result in considerable commercial advantage.

Carcase and meat quality in ducks killed with either gas mixtures or an electric current under commercial processing conditions

1. The feasibility of killing 7-week old Peking ducks with gas mixtures and their effects on carcase and meat quality were evaluated and compared with killing in electrical waterbath under commercial conditions. 2. The prevalence of carcase appearance defects and broken bones in the carcases and haemorrhaging, pH, colour, cooking loss and texture of breast muscles were determined. 3. Ducks can be killed within 3 min by exposure to either 90% argon in air or a mixture of 30% carbon dioxide and 60% argon in air. 4. Gas or controlled-atmosphere killing of ducks, whilst they are still in their transport containers, would eliminate some of the welfare concerns associated with the conventional electrical waterbath stunning systems, without adversely affecting carcase and meat quality.

The design of pig stunning tong electrodes-A review.

The effectiveness of current electrical stunning systems for pigs is discussed and the need for improvements in the design and construction of stunning tongs and electrodes are explored. A review of existing stunning tong electrodes for use with free standing or restrained pig is discussed. The potential problems with existing systems are highlighted as: (1) the profile of the pigs head precludes the application of existing electrodes in the correct position; (2) the small area of contact enhances carbon build-up which increases electrical impedance; (3) the electrodes are easily tarnished with few cleaning tools provided. Good tong positions that span the brain are described as between the eye and ear on each side of the head, below the ear on each side of the head or, diagonal application between the top and bottom of the head. The notional contact impedance is the major component of resistance to current flow within the stunning system. The proposed use of different electrode designs and constructional material is investigated. The effect of the introduction of the fail-safe device would be to heighten the interest in contact impedance within the plant and that could ensure that the investigation of different electrodes is explored at least at plant level.