Could low atmospheric pressure stunning (LAPS) be suitable for pig slaughter? A review of available information

Characterizing candidate decompression rates for hypobaric hypoxic stunning of pigs. Part 1: Reflexive behavior and physiological responses

Alternatives to carbon dioxide (CO2) stunning for the commercial slaughter of pigs are urgently needed because there is robust evidence that exposing pigs to hypercapnic environments is associated with pain, fear, and distress. Hypobaric hypoxia (via gradual decompression, also known as Low Atmospheric Pressure Stunning or LAPS) has been validated in poultry as a humane option, but its potential to improve the welfare of pigs at slaughter is unknown. We investigated the potential of hypobaric hypoxia to reliably elicit a non-recovery state in anesthetized weaner-grower pigs within a commercially viable timeframe. We determined the effect of candidate decompression rates (40, 60, 80, 100 ms−1, at two cycle durations 480 s and 720 s) on a range of physiological and reflexive behavioral indicators of hypoxia and death. We found that the decompression rates tested caused a 100% death rate. As expected, the decompression rate had overarching effects on behavioral and physiological markers of hypoxia and death, with faster decompression rates resulting in shorter latencies to cardiac arrest and cessation of breathing. We observed a higher proportion of pigs displaying repeated and prolonged whole-body movements (likely indicative of convulsive activity) at higher frequencies when we applied the slowest decompression rate (40 ms−1) compared to all other rates. Since these responses may impact the carcass and meat quality, the slower rate of decompression (40 ms−1) should be excluded as a candidate decompression rate. Furthermore, given the marginal effects of decompression rate on physiological indicators of death and reflexive behavioral parameters, we also recommend that the fastest rate tested (100 ms−1) is excluded in further study on conscious pigs (to prevent conscious animals from being exposed to unnecessary faster decompression rates which may compromise animal welfare). This work represents a necessary proof of principle step and confirms the potential of gradual decompression for stunning purposes in pigs. Importantly, however, the data presented provide no information on the welfare outcomes associated with decompression in conscious pigs. Subsequent work should focus on the comprehensive welfare assessment of intermediate decompression rates to determine the potential of hypobaric hypoxia to provide a humane stunning method for pigs.

Characterizing candidate decompression rates for hypobaric hypoxic stunning of pigs. Part 2: Pathological consequences

Pigs are commonly stunned pre-slaughter by exposure to carbon dioxide (CO2), but this approach is associated with significant welfare concerns. Hypobaric hypoxia, achieved with gradual decompression (also known as Low Atmospheric Pressure Stunning or LAPS) may be an alternative, allowing the retention of welfare friendly handling approaches and group stunning. Although validated in poultry, the feasibility and welfare consequences of gradual decompression for pigs are unknown. Here, we characterize pathological changes in 60 pigs resulting from exposure to a range of candidate decompression curves (ranging from 40 to 100 ms-1 ascent equivalent, with two cycle durations 480 and 720 s). To protect welfare, we worked on unconscious, terminally anesthetized pigs which were subject to detailed post-mortem examinations by a specialized porcine veterinary pathologist. All pigs were killed as a result of exposure to decompression, irrespective of cycle rate or length. Pigs showed no external injuries during ante-mortem inspections. Exposing pigs to decompression and the unavoidable subsequent recompression resulted in generalized congestion of the carcass, organs and body cavities including the ears, oral cavity, conjunctivae and sclera, mucosa of other external orifices (anus and vulva), nasal planum, nasal cavities including nasal conchae, frontal sinuses, cranium, meninges, brain, larynx, trachea, lungs, heart, parietal pleura of the thoracic cavity, peritoneum of the abdominal cavity, stomach, small intestine, caecum, colon, liver, spleen and kidneys and representative joint cavities in the limbs (stifles and elbows). Various severities of hemorrhage were observed in the conjunctivae and sclera, mucosa of other external orifices (anus and vulva), nasal cavities including nasal conchae, frontal sinuses, cranium, meninges, brain, larynx, tracheal lumen, lungs, parietal pleura of the thoracic cavity, liver, spleen and kidneys and representative joint cavities in the limbs (stifles and elbows). In general, faster decompression rates produced higher scores, but in the conjunctivae, sclera and kidneys, faster decompression rates were associated with marginally lower congestion scores. There was considerable individual variation in pathological scores across all body regions. The congestion and hemorrhage observed could translate into welfare harms in conscious pigs undergoing this type of stunning, depending when in the cycle the damage is occurring, but no welfare related conclusions can be drawn from the responses of unconscious pigs. Since recompression is always required, its effects cannot be separated from decompression, however cessation of cardiac activity several minutes before recompression should have eliminated any haemodynamic effects relating to cardiac function and blood pressure. This study represents the first systematic attempt to identify candidate rate profiles to underpin future explorations of decompression as a stunning method for pigs. These pathological findings also inform discussions about the likely carcass quality implications of this novel stunning method.

On-farm culling methods used for pigs

The culling of injured and non-viable pigs (Sus scrofa) (neonate to breeding stock) is a routine and necessary procedure on most farms. Usually, pigs are culled using one of the following methods: blunt-force trauma (manual and mechanical), captive-bolt stunners, electrical stunning and electrocution or carbon dioxide. Manual blunt-force trauma is one of the most widely used methods due to its low or absent operational and investment costs. However, as a method, it has serious limitations, which include the risk of incomplete concussion, pain, and distress. Manual blunt-force trauma is also aesthetically unpleasant to operators and wider society. To address these issues there has been significant recent research into the development of alternatives to manual blunt-force trauma, these include: captive-bolt stunners, on-farm, gas-based controlled atmosphere systems, low atmospheric pressure systems and electrical stunning. Some of these are currently in commercial use while others are still in the developmental phase. This review brings together the relevant research in this field, evaluating the methods in terms of mechanism of action (mechanical and physiological), effectiveness and animal welfare.

Review: Potential alternatives to high-concentration carbon dioxide stunning of pigs at slaughter

Using carbon dioxide (CO₂) for stunning pigs at slaughter is common in Europe. The use of group stunning is a major advantage with CO₂, which is done without restraining the pigs and with minimized human contact. However, high concentrations of CO₂ have been known for decades to cause pain, fear and distress in pigs before loss of consciousness, and the stunning method is clearly associated with animal welfare concerns. This study reviewed the scientific literature to find recent developments or evaluations of alternative methods that could lead to the replacement of CO₂ for stunning pigs at slaughter. Potential alternative methods found in the literature were described and then assessed to identify specific research and development needs for their further development. Only 15 empirical studies were found in the search of peer-reviewed literature since 2004, which is less than one per year. Furthermore, half of the studies focused on evaluating methods to improve high-concentration CO₂ stunning rather than an alternative to CO₂. Since no clear alternative has emerged, nor a method to improve CO₂ stunning, there is obviously a strong need to focus research and development to find solutions for improving animal welfare when stunning pigs at slaughter.