Evaluation of Alternative Euthanasia Methods of Neonatal Chickens

The use of high expansion foam for stunning and killing pigs and poultry

The EFSA Panel on Animal Health and Welfare (AHAW) was asked to deliver a scientific opinion on the use of high-expansion foam for stunning and killing pigs and poultry. A dossier was provided by the applicant as the basis for an assessment of the extent to which the method is able to provide a level of animal welfare at least equivalent to that ensured by the currently allowed methods for pigs and poultry. According to legislation, to be approved in the EU, new stunning methods must ensure (1) the absence of pain, distress or suffering until the onset of unconsciousness, and (2) that the animal remains unconscious until death. An ad hoc Working Group set up by EFSA performed the assessment as follows: (1) The data provided were checked against the criteria laid down in the EFSA Guidance (EFSA, 2018), and was found to partially fulfil those criteria; (2) extensive literature search; (3) data extraction for quantitative assessment; (4) qualitative exercise based on non-formal expert elicitation. The assessment led to conclude that it is more likely than not (certainty > 50%-100%) that high-expansion foam for stunning and killing pigs and poultry, named NEFS in container (Nitrogen Expansion Foam Stunning in container), provides a level of welfare at least equivalent to one or more of the currently allowed methods listed in Annex I of Council Regulation (EC) No 1099/2009. The overall assessment of EFSA is valid only under the technical conditions described in this Opinion for laying hens, broiler chickens of all age and pigs weighing 15-41 kg in situations other than slaughter. The overall assessment of EFSA is that NEFS can be suitable for depopulation using containers for pig and poultry farms respecting the technical conditions and the categories and types of animals defined in this Scientific Opinion.

Evaluation of mechanical cervical dislocation, captive bolt, carbon dioxide, and electrical methods for individual on-farm euthanasia of broiler breeders

Efficacious euthanasia by applying manual cervical dislocation can be difficult on large and mature poultry. The challenge with using manual cervical dislocation is that the strength required to hold heavy poultry and swiftly apply cervical dislocation can be physically impossible for most people. Therefore, alternative methods of euthanasia are needed for mature and large poultry. Mechanical cervical dislocation using the Koechner Euthanizing Device (KED), captive bolt using the Turkey Euthanasia Device (TED), carbon dioxide (CO₂), and electrical euthanasia were evaluated for use on 65-wk-old broiler breeders at flock termination. Following application of each method, physiological reflexes including the eye nictitating membrane reflex, mouth gaping, and body movement, broken skin, blood loss, kill success, time to cessation of heartbeat, and blood plasma corticosterone levels were assessed. Birds euthanized using the KED had longer response durations for eye nictitating membrane (91 s) and reflexive mouth gaping (161 s) compared to TED, CO₂, and electrical euthanasia (0–7 s). Body movement durations were also longer for KED (214 s) and TED (209 s) than for CO₂ and electrical euthanasia (0–8 s). The highest percentages of broken skin (93%) and blood loss (96%) were observed for TED, followed by KED (71%, 68%), then CO₂ (0%, 6%) and electrical euthanasia (0%, 3%). No significant differences (P = 0.1781) were observed for kill success rates with 98% for KED, 100% for TED, 97% for CO₂, and 100% for electrical euthanasia at 4-min. Time to heartbeat cessation did not differ between KED (659 s), TED (427 s), or CO₂ (583 s) euthanasia methods. No heartbeat was detected following electrical euthanasia. Blood plasma corticosterone levels did not differ between preeuthanasia or posteuthanasia from any of the methods applied. Based on these results each euthanasia method is acceptable for use with broiler breeders.

Applied Animal Ethics in Industrial Food Animal Production: Exploring the Role of the Veterinarian

Industrial food animal production practices are efficient for producing large quantities of milk, meat, and eggs for a growing global population, but often result in the need to alter animals to fit a more restricted environment, as well as creating new animal welfare and health problems related to animal confinement in high densities. These practices and methods have become normalized, to the extent that veterinarians and others embedded in these industries rarely question the ethical challenges associated with raising animals in this fashion. Moral ‘lock-in’ is common with those working in food animal industries, as is the feeling that it is impossible to effect meaningful change. Animal welfare issues associated with the industrialization of food animal production are ‘wicked problems’ that require a multi- and transdisciplinary approach. We argue that veterinarians, as expert animal health and welfare advocates, should be critical stakeholders and leaders in discussions with producers and the food animal sector, to look for innovative solutions and technology that will address current and future global sustainability and food security needs. Solutions will necessarily be different in different countries and regions, but ethical issues associated with industrial food animal production practices are universal.

Comparison of Gaseous and Water-Based Medium-Expansion Foam Depopulation Methods in Cull Sows

Simple Summary

In the face of a swine health crisis, emerging zoonotic diseases or environmental catastrophe, the mass depopulation of swine may be required to prevent the additional spread of disease and to minimize animal pain or suffering. Due to the increasing risk of global disease outbreaks, the U.S. swine industry needs feasible guidelines in place in preparation for such events. Current American Veterinary Medical Association (AVMA) approved swine depopulation methods can be difficult to implement under field conditions. Emergency depopulation using inhalants such as carbon dioxide (CO₂) and nitrogen gas (N₂) or the use of aspirated foam agents have been approved and conducted in poultry in the US, but are not approved for use in other livestock. Our findings, using cull sows, demonstrate that although CO₂, N₂ and aspirated foam combinations successfully killed all the animals, CO₂ and aspirated foam did so in the shortest timeframe. In addition, the use of aspirated foam was as effective as CO₂ for sow depopulation while having potential operational advantages, such as no use of lethal gases and reduced risk of associated equipment failure.

Abstract

The U.S. swine industry is currently inadequately prepared to counteract the increasing threat of high-consequence diseases. Although approved and preferred depopulation guidelines exist, ventilation shutdown (VSD+) is currently the only method being deployed during a state of emergency to depopulate large swine populations. However, the permitted use of VSD+ during constrained circumstances has been criticized due to raised swine welfare concerns. The objective of this study was to investigate the effectiveness of carbon dioxide gas (CO₂), nitrogen gas (N₂), compressed air foam (CAF), compressed nitrogen foam (CAF-N₂) and aspirated foam (AF) during a 15-min dwell time on adult swine in an emergency depopulation situation. A small-scale trial using 12 sows per depopulation method showed the highest efficiency to induce cessation of movement for AF and CO₂ (186.0 ± 48 vs. 202.0 ± 41, s ± SD). The ease of implementation and safety favored AF for further investigation. A large-scale field study using AF to depopulate 134 sows in modified rendering trailers showed a mean fill time of 103.8 s (SD: 5.0 s) and cessation of movement of 128.0 s (SD: 18.6 s) post filling. All sows were confirmed dead post-treatment for both trials. The implementation of AF in modified rendering trailers may allow for a safe and reliable method that allows for the expedient and mobile depopulation of both small and large numbers of sows during an emergency.

The Need for an Alternative to Culling Day-Old Male Layer Chicks: A Survey on Awareness, Alternatives, and the Willingness to Pay for Alternatives in a Selected Population of Dutch Citizens

A concerning by-product of producing laying hen chicks are the hatched male layer chicks. As a consequence of their inability to lay eggs, these male chicks are culled as day-old chicks in the hatchery. To find an alternative for this ethical dilemma (generally), three alternatives are under study, namely, in ovo sex determination, using dual-purpose breeds, and the rearing of layer cockerels. In order to assess the awareness of this practice and preference for one of the alternatives, we conducted an online survey of the Dutch public. Most of the 259 respondents completing the survey were highly educated woman (HEW, n = 143) versus others (REST, n = 86). The questionnaire was divided into six topics: (1) general knowledge of the poultry industry, (2) awareness of culling male layer chicks (CMC), and (3) its acceptability, (4) alternatives to CMC, (5) willingness to pay (WTP) for eggs without CMC, and (6) WTP for cockerel meat. Awareness about CMC was 52%, and its acceptability was rejected by 78% (HEW) and 67% (REST). The level of acceptability increased when more salient facts were given, and almost all respondents agreed that an alternative was needed (90% HEW, 84% REST). For both groups of respondents, more than 50% preferred in ovo sex determination over keeping the current practice or using dual-purpose breeds or male layers. Furthermore, the majority of respondents were willing to pay more than double the price for eggs without CMC being involved. Roughly 40% would not buy processed cockerel meat burgers, most likely due to their vegan or vegetarian diet. Of the remaining respondents, half were willing to pay the current price or 1 euro more for processed cockerel meat burgers. The most important factors when buying poultry meat or eggs without CMC were food safety, animal friendliness (welfare), and the environment; price was the least important factor. Despite the skewed respondents' background, the results of our survey show that consumers are willing to pay more for poultry products that do not require culling day-old male chicks.

Evaluation of Euthanasia Methods on Behavioral and Physiological Responses of Newly Hatched Male Layer Chicks

Newly hatched male layer chicks are considered as "by-products" in the egg industry and must be humanely euthanized at the hatchery. Instantaneous mechanical destruction (maceration) is the predominant euthanasia method applied in poultry hatcheries and is approved by the American Veterinary Medical Association (AVMA). However, maceration is not perceived by the public to be a humane means of euthanasia. The effects of alternative euthanasia methods, including carbon dioxide (CO₂) or nitrogen (N₂) inhalation, and a commercial negative pressure stunning system on behavioral and physiological responses of day-of-hatch male layer chicks, were evaluated in a field trial. Chick behaviors, including ataxia, loss of posture, convulsions, cessation of vocalization, and cessation of movement, were monitored. Serum hormones were assessed at the end of each of the alternative euthanasia treatments, including a control group allowed to breathe normal atmospheric air. The N₂ method induced unconsciousness and death later than the CO₂ and negative pressure methods, and increased serum corticosterone concentrations of neonatal chicks. Carbon dioxide inhalation increased serotonin concentrations as compared to controls, as well as the N₂ and the negative pressure methods. The behavioral and physical responses observed in this study suggest that both CO₂ inhalation and negative pressure stunning can be employed to humanely euthanize neonatal male layer chicks.

Animal welfare assessment of on-farm euthanasia methods for individual, heavy turkeys

On-farm euthanasia of poultry, including turkeys, may not be possible for most people as birds gain weight; thus alternative mechanical methods have been developed. Our objective was to compare mechanical cervical dislocation with the Koechner Euthanizing Device (KED), captive bolt euthanasia with the Turkey Euthanasia Device (TED), head-only CO₂ euthanasia (CO₂), and electric euthanasia as potential humane methods for euthanizing individual, heavy turkeys. We assessed their impact on loss of brain stem reflexes, acute distress (corticosterone, CORT), kill success, torn skin, and blood loss. Turkeys (n = 174) were euthanized on 3 sampling days, while birds were restrained using a mobile bird euthanasia apparatus. Brain stem reflexes recorded were the cessation and return of induced nictitating membrane reflex (loss of consciousness and brain stem dysfunction), mouth gaping reflex (brain stem dysfunction), and musculoskeletal movements (spinal cord dysfunction). Overall, KED resulted in more frequent (at 4 min: KED 7 of 14; electric 0 of 13; TED 0 of 11; CO₂ 2 of 14 birds on day 1) and longer durations of the induced nictitating reflex compared to the other methods (means of day 2 and 3: KED 233; electric 15; TED 15; CO₂ 15 s). The mouth gaping reflex endured the longest after KED euthanasia (means of day 2 and 3: KED 197; electric 15; TED 51; CO₂ 15 s). Musculoskeletal movements endured longest after KED euthanasia (means of day 2 and 3: KED 235; electric 15; TED 219; CO₂ 15 s). Returning reflexes were more frequent after KED and TED compared to CO₂ and electric euthanasia, where it was absent. CO₂, electric, and TED euthanasia showed comparable kill success (success: CO₂ 42 out of 43; electric 44 of 45; TED 42 of 44), with KED resulting in most unsuccessful kills (unsuccessful: 8 out of 42). CORT responses were inconsistent. Torn skin and blood loss occurred more frequently after KED and TED compared to CO₂ and electric applications. Therefore, we conclude that, based on a comparison of these 4 methods, the most discernibly humane was electric euthanasia, which consistently resulted in quick loss of consciousness within 15 s, no returning reflexes, and no torn skin or blood loss.

Incubation, hatchery practice and the welfare of layer hens

For modern layers to achieve optimum production performance and welfare state, the entire production process needs to be managed to achieve target bodyweight, body composition and flock uniformity. In addition to genetic improvements, flock health, environment, nutrition and on-farm husbandry practices, incubation and hatchery practices have become a focal point for producing optimum chick quality. Chick quality is a collective term involving chick size and anatomical features, physiology, robustness and liveability over the first week after placement. Chick quality is a key focus for hatcheries as this has been positively correlated with overall flock performance, especially egg production, shell quality, liveability and animal welfare. Recent advances in incubation have focussed on the benefits of all-in–all-out (single-stage) machines. Innovation in incubation systems is completely conducted today by international manufacturers, and is largely driven by the meat chicken industry. Disposal of male layer chicks has increased as a consumer welfare concern, and while investment in research and legislation changes are focussed towards providing or driving new solutions, there are currently no commercial options for industry to deal with this problem before incubation or hatch. Chick transport systems and equipment have also significantly improved in recent years, providing optimum conditions to ensure temperature uniformity and minimal moisture loss during transit before placement, thus optimising chick quality. Together, recent improvements in incubation equipment and hatchery practice can produce commercial layer chicks that are healthy, of high quality, and are then in an optimal physiological state and condition to achieve their genetic potential.

Euthanasia of laying hens: an overview

Euthanasia of an animal requires that its death occurs in as humane a manner as possible. There are three key scenarios for euthanasia in the egg industry: the humane destruction of day-old male chicks, euthanasia of individual birds, and the depopulation of flocks for disease control or because conventional transport and slaughter is uneconomic. For day-old chicks, instant mechanical maceration, although conditionally humane, presents a public perception problem. Submerging in CO2 gas is less confronting but is thought to be aversive to animals unless more expensive and harder to manage inert gases are incorporated. Future technologies involving pre-hatching sex determination or sex selection may largely solve the problem when fully developed. For the euthanasia of individual birds within the flock, manual cervical dislocation has been shown to be humane when performed by trained personnel who are willing to perform the procedure. Penetrating and non-penetrating mechanical devices that cause irreversible brain trauma are becoming more available and represent a humane alternative to cervical dislocation when properly placed and maintained. These devices may be less confronting for some staff to use than is cervical dislocation. For whole-flock euthanasia, the overwhelming requirements of disease control and public safety may override considerations of euthanasia. Whole-shed CO2 (or other gas combinations) and foam-based alternatives can be used, but have challenges in commercial settings. Modified atmosphere killing units or low atmospheric stunning systems are alternatives that overcome some of these practical problems, but do require birds to be handled.

Aerosol delivery of synthetic DNA containing CpG motifs in broiler chicks at hatch under field conditions using a commercial-scale prototype nebulizer provided protection against lethal Escherichia coli septicemia

Synthetic DNA containing CpG motifs (CpG-ODN) are potent innate immune stimulators in neonatal and adult broiler chickens against bacterial septicemia. We have recently demonstrated that intrapulmonary (IPL) delivery of CpG-ODN as microdroplets under laboratory conditions can protect neonatal chickens against lethal Escherichia coli septicemia. The objectives of this study were to develop a commercial-scale poultry nebulizer (CSPN) that can deliver CpG-ODN as microdroplets in neonatal broiler chicks in the hatcheries and study the efficacy of CSPN in inducing immune-protective effects under different environmental conditions in 2 geographical locations in Canada. Three field experiments were conducted in commercial poultry hatcheries during different seasons of the year in Saskatchewan and British Columbia, Canada. Neonatal broiler chicks (n = 8,000/experiment) received CpG-ODN by the IPL route in the CSPN chamber for 30 min, and control chicks received distilled water (DW) for 30 min. Broiler chicks (CpG-ODN—240 chicks/experiment and DW—40 chicks/experiment) were randomly sampled from all locations of the CSPN after nebulization and challenged with a lethal dose of E. coli to examine the CpG-ODN nebulization induced protection. We found a significant level (P < 0.05) of protection in broiler chicks against E. coli challenge, suggesting that the newly built CSPN successfully delivered CpG-ODN via the IPL route. We found that when the CSPN was maintained at humidex 28°C or below and relative humidity (RH) between 40 and 60%, neonatal birds were significantly (P < 0.05) protected against E. coli septicemia after IPL delivery of CpG-ODN. By contrast, protection in chicks was adversely affected when the CSPN was maintained at the humidex of 29°C or higher and RH of 70%. Overall, the present study successfully built a CSPN for CpG-ODN delivery in chicks at the hatchery and revealed that the temperature, humidity, and humidex were critical parameters in CSPN for efficient delivery of CpG-ODN.

COVID-19 Effects on Livestock Production: A One Welfare Issue

The COVID-19 pandemic highlights that we exist in a global community. From a single city, it spread to 188 countries across the world and infected 30 million people by September 18, 2020. Decades of modeling pandemics predicted potential consequences, but COVID-19's impact on the food supply chain, and specifically livestock production was unexpected. Clusters of cases among workers in meat processing plants evolved quickly to affect human, animal, and environmental welfare in several countries. In processing plants, the hygiene focus is on product quality and food safety. Because of their close proximity to one another, COVID-19 spread rapidly between workers and the lack of sick leave and health insurance likely resulted in workers continuing to work when infectious. In the United States (U.S.) many processing plants shut down when they identified major outbreaks, putting pressure especially on pig and poultry industries. At one point, there was a 45% reduction in pig processing capacity meaning about 250,000 pigs per day were not slaughtered. This resulted in longer transport distances to plants in operation with extra capacity, but also to crowding of animals on farm. Producers were encouraged to slow growth rates, but some had to cull animals on farm in ways that likely included suffering and caused considerable upset to owners and workers. Carcass disposal was also associated with potential biosecurity risks and detrimental effects on the environment. Hence, this is a One Welfare issue, affecting human, animal, and environmental welfare and highlighting the fragility of intensive, high-throughput livestock production systems. This model needs to be re-shaped to include the animal, human, and environmental elements across the farm to fork chain. Such a One Welfare approach will ensure that food production systems are resilient, flexible, and fair in the face of future challenges.

Defining characteristics of immersion carbon dioxide gas for successful euthanasia of neonatal and young broilers

This study investigated how the carbon dioxide (CO₂) concentration within a chamber affects the efficacy of CO₂ euthanasia and how the efficacy of CO₂ induction methods changes as birds age. In experiment 1, pairs of broiler chicks (n = 192; 0, 3, and 6 D of age) were immersed into a chamber prefilled with 70, 80, 90, or 100% CO_2. For experiment 2, 3- and 6-day-old broiler chicks (n = 88) were immersed in pairs into 100% CO₂ or exposed to CO₂ gradual fill in a chamber with a displacement rate of 28% chamber volume per minute. Latency to performance of headshaking (HS) and gasping (GS) as potential indicators of distress, loss of posture indicative of insensibility, and the cessation of rhythmic breathing (CRB) and cessation of movement (COM) as the indicators of death were monitored (live focal sampling/video recordings). The duration and frequency of HS and GS were assessed. For both experiments, behavior data were analyzed for CO₂ method and age (4 × 3 factorial). Age and CO₂ concentration interacted for latency to CRB and COM, with longer latencies for 0-day-old chicks immersed into 70% CO₂ than other concentrations and ages. CO₂ concentration did not affect latency to HS, GS, or loss of posture but affected CRB and COM, with latencies longest for 70% and shortest for 90 and 100% CO₂. Newly hatched chicks had a longer latency to CRB and COM and longer duration and frequency of distress behaviors than older chicks. At all ages, initiation of all behaviors occurred later with gradual fill compared to immersion. There was an increased duration and frequency of distress behaviors with gradual induction compared with immersion. Overall, immersion into 90 to 100% CO₂ resulted in the shortest time to insensibility and death, with a decreased duration and frequency of distress behaviors. Chicks immersed into 70% CO₂ had the longest duration of GS and time to death. Age affects the efficacy of CO₂ euthanasia, with increasing age decreasing time to death and the duration and frequency of distress behaviors.

Humanely Ending the Life of Animals: Research Priorities to Identify Alternatives to Carbon Dioxide

: The use of carbon dioxide (CO2) for stunning and killing animals is considered to compromise welfare due to air hunger, anxiety, fear, and pain. Despite decades of research, no alternatives have so far been found that provide a safe and reliable way to induce unconsciousness in groups of animals, and also cause less distress than CO2. Here, we revisit the current and historical literature to identify key research questions that may lead to the identification and implementation of more humane alternatives to induce unconsciousness in mice, rats, poultry, and pigs. In addition to the evaluation of novel methods and agents, we identify the need to standardise the terminology and behavioural assays within the field. We further reason that more accurate measurements of consciousness state are needed and serve as a central component in the assessment of suffering. Therefore, we propose a roadmap toward improving animal welfare during end-of-life procedures.

Killing for purposes other than slaughter: poultry

Poultry of different ages may have to be killed on-farm for purposes other than slaughter (in which slaughtering is defined as being for human consumption) either individually or on a large scale (e.g. because unproductive, for disease control, etc.). The processes of on-farm killing that were assessed are handling and stunning and/or killing methods (including restraint). The latter were grouped into four categories: electrical methods, modified atmosphere, mechanical methods and lethal injection. In total, 29 hazards were identified and characterised, most of these regard stunning and/or killing. Staff were identified as origin for 26 hazards and 24 hazards were attributed to lack of appropriate skill sets needed to perform tasks or due to fatigue. Specific hazards were identified for day-old chicks killed via maceration. Corrective and preventive measures were assessed: measures to correct hazards were identified for 13 hazards, and management showed to have a crucial role in prevention. Eight welfare consequences, the birds can be exposed to during on-farm killing, were identified: not dead, consciousness, heat stress, cold stress, pain, fear, distress and respiratory distress. Welfare consequences and relevant animal-based measures were described. Outcome tables linking hazards, welfare consequences, animal-based measures, origins, preventive and corrective measures were developed for each process. Mitigation measures to minimise welfare consequences were also proposed.

Suitability of layer-type male chicks for capon production

The aim of this study was to determine the effect of age and caponization on the growth performance and carcass quality characteristics of Leghorn cockerels. The experiment was conducted on 224 Leghorn cockerels. At 8 wk of age, 112 birds were surgically castrated by a qualified veterinarian in accordance with Commission Regulation (EC) No. 543/2008. The birds were divided into 2 sex categories (with 8 replications per group and 14 birds per replication). The birds were raised to 28 wk of age, and were fed commercial diets ad libitum. From 12 wk of age, at 4-wk intervals, 8 intact cockerels and 8 capons (1 bird per replication) were selected randomly and slaughtered. Caponization had a beneficial influence on the feed conversion ratio (FCR). FCR (kg/kg) based on body weight (BW) gain, carcass weight gain, and edible weight gain was lower in capons from 24 wk of age (P < 0.05), and FCR based on lean weight gain was lower in capons from 21 wk of age (P < 0.05). The content of edible components expressed as a percentage of the total BW of cockerels and capons was similar in the corresponding age groups. Caponization had no effect on the total lean meat content of the carcass (P = 0.744), but differences were found between the weights of breast muscles and leg muscles. In week 24 and 28, the weight of breast muscles was higher in capons than in cockerels (P < 0.05). Cockerels had higher leg muscle weight than capons, and significant differences were noted in week 16 and in 28 (P < 0.05).

Evaluation of carbon dioxide induction methods for the euthanasia of day-old cull broiler chicks

This study was conducted to evaluate the efficacy of 5 different CO2 euthanasia induction techniques for day-old cull chicks in minimizing distress and inducing a rapid loss of sensibility and death. Each induction treatment was characterized for concentration change over time, maximum concentration, and time to reach maximum. Sixteen chicks were euthanized with the gradual treatments to establish validity of treatment. Then, all 5 treatments were evaluated for effect on distress, insensibility, and death. Day-of-hatch cull chicks (n = 110) were euthanized in pairs by either immersion into 100% CO2 or gradual induction to 100% CO2 at displacement rates of 7, 14, 21, or 28% of chamber volume added per min (% vol/min). CO2 concentration was measured at chick level. Live focal observations and video recordings were used to assess latency to behavioral responses: head shaking (HS) and gasping (GS) as indicators of distress; loss of posture (LOP) as an indicator of insensibility; and cessation of rhythmic breathing (CRB) and movement (COM), indicating death. All behaviors occurred at the earliest with immersion compared to gradual treatments, and time between first signs of distress and LOP was shorter for immersion than gradual treatments. Gradual treatments showed a linear decrease in latency to HS, GS, and LOP as displacement rate increased. Latency to CRB decreased quadratically with increasing displacement rate, while COM decreased linearly. Within gradual treatments, HS and GS occurred at CO2 concentrations between 0.43 and 1.14%, LOP between 11.1 and 17.5%, while CRB and COM occurred between 61.8 and 78.4%. Overall, immersion induced distress, insensibility, and death significantly faster and with the shortest interval between distress and insensibility. For gradual treatment, insensibility and death occurred faster with increasing displacement rates. Behavioral signs of distress were observed with all treatments, and occurred at concentrations lower than those causing insensibility. In conclusion, immersion into 100% CO2 environment resulted in the shortest time of distress and fastest time to death compared to gradual displacement rates of any speed measured.