Assessing a Method of Mechanical Cervical Dislocation as a Humane Option for On-Farm Killing Using Anesthetized Poults and Young Turkeys

Avian Influenza: Strategies to Manage an Outbreak

Avian influenza (AI) is a contagious disease among the poultry population with high avian mortality, which generates significant economic losses and elevated costs for disease control and outbreak eradication. AI is caused by an RNA virus part of the Orthomyxoviridae family; however, only Influenzavirus A is capable of infecting birds. AI pathogenicity is based on the lethality, signs, and molecular characteristics of the virus. Low pathogenic avian influenza (LPAI) virus has a low mortality rate and ability to infect, whereas the highly pathogenic avian influenza (HPAI) virus can cross respiratory and intestinal barriers, diffuse to the blood, damage all tissues of the bird, and has a high mortality rate. Nowadays, avian influenza is a global public health concern due to its zoonotic potential. Wild waterfowl is the natural reservoir of AI viruses, and the oral-fecal path is the main transmission route between birds. Similarly, transmission to other species generally occurs after virus circulation in densely populated infected avian species, indicating that AI viruses can adapt to promote the spread. Moreover, HPAI is a notifiable animal disease; therefore, all countries must report infections to the health authorities. Regarding laboratory diagnoses, the presence of influenza virus type A can be identified by agar gel immunodiffusion (AGID), enzyme immunoassay (EIA), immunofluorescence assays, and enzyme-linked immunoadsorption assay (ELISAs). Furthermore, reverse transcription polymerase chain reaction is used for viral RNA detection and is considered the gold standard for the management of suspect and confirmed cases of AI. If there is suspicion of a case, epidemiological surveillance protocols must be initiated until a definitive diagnosis is obtained. Moreover, if there is a confirmed case, containment actions should be prompt and strict precautions must be taken when handling infected poultry cases or infected materials. The containment measures for confirmed cases include the sanitary slaughter of infected poultry using methods such as environment saturation with CO₂, carbon dioxide foam, and cervical dislocation. For disposal, burial, and incineration, protocols should be followed. Lastly, disinfection of affected poultry farms must be carried out. The present review aims to provide an overview of the avian influenza virus, strategies for its management, the challenges an outbreak can generate, and recommendations for informed decision making.

A decade on: where is the UK poultry industry for emergency on-farm killing?

Millions of poultry are farmed intensively every year across the United Kingdom (UK) to produce both meat and eggs. There are inevitable situations that require birds to be emergency killed on farm to alleviate pain and suffering. In Europe and the UK, emergency methods are regulated by the European Council Regulation (EC) No. 1099/2009 and The Welfare of Animals at the Time of Killing Regulations (England 2015; Scotland 2012; Wales and Northern Ireland 2014). Cervical dislocation has been reported to be the most widely used method prior to these legislative changes which took place from 1 January 2013. Based on limited scientific evidence and concern for bird welfare, these legislative changes incorporated restrictions based on bird weight for both manual (≤3 kg) and mechanical (≤5 kg) cervical dislocation, and introduced an upper limit in the number of applications for manual cervical dislocation (up to 70 birds per person per day). Furthermore, it removed methods which showed evidence of crushing injury to the neck. However, since legal reform new scientific evidence surrounding the welfare consequences of cervical dislocation and the development of novel methods for killing poultry in small numbers on farm have become available. Whether the UK poultry industry have adopted these novel methods, and whether legislative reform resulted in a change in the use of cervical dislocation in the UK remains unknown. Responses from 215 respondents working across the UK poultry industry were obtained. Despite legal reform, manual cervical dislocation remains the most prevalent method used across the UK for killing poultry on farm (used by 100% of farms) and remains the preferred method amongst respondents (81.9%). The use of alternative methods such as Livetec Nex® and captive bolt guns were available to less than half of individuals and were not frequently employed for broilers and laying hens. Our data suggests there is a lack of a clear alternative to manual cervical dislocation for individuals working with larger species and a lack of gold standard methodology. This risks bird welfare at killing and contributes to inconsistency across the industry. We suggest providing stakeholders with practical alternatives prior to imposing legislative changes and effective knowledge transfer between the scientific community and stakeholders to promote positive change and protect bird welfare.

Efficacy of three different cervical dislocation methods for on-farm killing of layer chicks

Unfit chicks with low viability are often euthanized in the layer industry. An effective euthanasia protocol is characterized by rapid, irreversible insensibility, followed by prompt death. This study was conducted to evaluate the efficacy of three cervical dislocation methods for killing layer chicks (2-3-day-old, avg BW ± SD; 44 ± 3 g, n = 40): manual cervical dislocation (CD), assisted manual cervical dislocation (ACD; the bird's ventral neck is placed on a blunt table edge and the back of the neck pressed firmly), and mechanical cervical dislocation by Koechner Euthanizing Device (KED-model-S). All three killing methods were assessed on anesthetized chicks (intramuscular injections of medetomidine [0.3 mg/kg BW] and ketamine [30 mg/kg BW] were used to induce clinical anesthesia). CD and ACD were also evaluated using conscious chicks to compare the killing methods and to determine the effect of anesthesia on response variables. There were no differences in time to loss of pupillary light reflex, cessation of heartbeat, or duration of gasping between conscious chicks killed with CD and ACD, but these values were all longer for conscious compared to anesthetized chicks. KED resulted in longer latencies to loss of pupillary light reflex, cessation of heartbeat, and duration of gasping. Radiographs revealed that both CD and ACD resulted in cervical luxation, mainly below the C4 vertebra, whereas KED did not cause luxation in any of the 8 chicks tested. Chicks killed by CD and ACD presented more subdural hemorrhage (SDH) at the site of cervical dislocation than those killed by KED. None of the killing methods resulted in brain trauma. Compared to CD and ACD, KED resulted in longer latency to brain death and less anatomical pathology indicating a lower efficacy of KED as an on-farm killing method.

Does wing use and disuse cause behavioural and musculoskeletal changes in domestic fowl (Gallus gallus domesticus)?

Domestic chickens may live in environments which restrict wing muscle usage. Notably, reduced wing activity and accompanying muscle weakness are hypothesized risk factors for keel bone fractures and deviations. We used radio-frequency identification (RFID) to measure duration spent at elevated resources (feeders, nest-boxes), ultrasonography to measure muscle thickness (breast and lower leg) changes, radiography and palpation to determine fractures and deviations, respectively, following no, partial (one-sided wing sling) and full (cage) immobilization in white- and brown-feathered birds. We hypothesized partially immobilized hens would reduce elevated resource usage and that both immobilization groups would show decreased pectoralis thickness (disuse) and increased prevalence of fractures and deviations. Elevated nest-box usage was 42% lower following five weeks of partial immobilization for brown-feathered hens but no change in resource usage in white-feathered birds was observed. Fully immobilized, white-feathered hens showed a 17% reduction in pectoralis thickness, while the brown-feathered counterparts showed no change. Lastly, fractures and deviations were not affected in either strain or form of wing immobilization; however, overall low numbers of birds presented with these issues. Altogether, this study shows a profound difference between white- and brown-feathered hens in response to wing immobilization and associated muscle physiology.

Wing-feather loss in white-feathered laying hens decreases pectoralis thickness but does not increase risk of keel bone fracture

Feather loss in domestic chickens can occur due to wear and tear, disease or bird-to-bird pecking. Flight feather loss may decrease wing use, cause pectoral muscle loss and adversely impact the keel bone to which these muscles anchor. Feather loss and muscle weakness are hypothesized risk factors for keel bone fractures that are reported in up to 98% of chickens. We used ultrasound to measure changes in pectoral muscle thickness and X-rays to assess keel bone fracture prevalence following symmetric clipping of primary and secondary feathers in white- and brown-feathered birds. Four and six weeks after flight feather clipping, pectoralis thickness decreased by approximately 5%, while lower leg thickness increased by approximately 5% in white-feathered birds. This pectoralis thickness decrease may reflect wing disuse followed by muscle atrophy, while the increased leg thickness may reflect increased bipedal locomotion. The lack of effect on muscle thickness in brown-feathered hens was probably due to their decreased tendency for aerial locomotion. Finally, pectoralis thickness was not associated with keel bone fractures in either white- or brown-feathered birds. This suggests that the white-feathered strain was more sensitive to feather loss. Future prevention strategies should focus on birds most susceptible to muscle loss associated with flight feather damage.

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.

The efficacy of three on-farm euthanasia methods for broiler chickens throughout the production cycle

1. There is a need to humanely kill moribund or injured broiler birds on-farm with no reasonable chance of recovery. Two experiments evaluated the efficacy of three commercially applicable killing methods; manual cervical dislocation (CD), mechanical cervical dislocation with the Koechner Euthanising Device (KED) and a non-penetrative captive bolt device (Zephyr-EXL; ZEXL), at 7, 21 or 35 d of age, on their ability to induce insensibility (unconsciousness and loss of brain stem reflexes) and death.2. Experiment one assessed the damage to the cranial-cervical region resulting from the methods applied to cadavers of cull birds (n = 180) by radiography and gross pathology observation.3. Experiment two evaluated the latency to insensibility and death when cull broiler birds (n = 240) were killed by CD, KED or ZEXL, using behavioural and reflexive indicators. Insensibility and death were measured by the absence of pupillary light, palpebral blink and nictitating membrane reflexes and cessation of rhythmic breathing, cloacal winking and convulsions. Analysis of variance for the main effect of the method was performed to determine the differences.4. In experiment one, only the Zephyr resulted in skull fractures. A higher number of vertebral fractures occurred with KED application compared to CD, at 21 and 35 d.5. In experiment two, indicators of sensibility were absent earliest with the ZEXL (μ < 2 s); then,CD (μ = 28 s) and were longest with KED (μ = 47 s), at 21 and 35 d. Cloacal winking and convulsions ceased earlier after CD (88 s), compared to either KED (124 s) or Zephyr (118 s). Death after a single application occurred 100%, 100% and 98% of time for CD, KED and ZEXL, respectively.6. Overall, all methods were efficacious at inducing insensibility and death. Insensibility occurred earliest with ZEXL, whilst death occurred earliest with CD. KED resulted in the longest time to insensibility and death.

Evaluation of intravenous T-61 as a euthanasia method for birds

The use of T-61 as a sole euthanasia agent for birds was investigated. Nine broiler chickens (Gallus gallus domesticus) were euthanized by intravenous T-61 and assessed for insensibility [brainstem reflexes: nictitating membrane reflex (NIC), palpebral blink reflex (PAL)], brain death [isoelectric electroencephalogram activity (EEG)], cessation of audible heartbeat, and abnormal electrocardiogram. Birds were considered dead when the heart rate was less than 180 beats/minute with an isoelectric EEG. No vocalization or wing flapping occurred. Both NIC and PAL were lost 10.5 s from start of injection and audible heartbeat ceased at 24.5 s. Latency to isoelectric activity was 16.6 s. All but 1 bird died within 60 s. Rapid induction of insensibility meant birds did not experience pain and distress within 10.5 s from start of injection and birds were not conscious during cardiac and circulatory arrest. Intravenous injection of T-61 is an effective and efficient euthanasia method for birds.

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.

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.

Evaluation of Brain Death in Laying Hens During On-Farm Killing by Cervical Dislocation Methods or Pentobarbital Sodium Injection

This study investigated changes in the electroencephalograph (EEG) power spectrum as well as physiological and behavioral responses to on-farm killing via mechanical cervical dislocation (MCD), manual cervical dislocation (CD) or intravenous pentobarbital sodium administration in lightly anesthetized laying hens, to evaluate the welfare impact of each method. A mixed group of 44 white Leghorn and Smoky Joe laying hens (60 weeks-old) were anesthetized with isoflurane in oxygen and maintained at 1.5–2% isoflurane/O₂ until the killing method was applied. Birds were randomly assigned to one of three experimental groups on each trial day. The EEG was recorded bilaterally in a four-electrode montage. After recording a 5-min baseline, the killing method was applied and EEGs and other behavioral and physiological responses, including convulsions, gasping, cessation of body movements and feather erection were recorded for 5 min. Changes in EEG frequency bands (alpha, beta, delta, theta), median frequency (F50), 95% spectral edge frequency (F95), and total power (Ptot) were used to assess the quality of the on-farm killing event. Within 15 s after administration of pentobarbital sodium, there were significant decreases in mean frequency bands, increases in mean F50 and F95, and decreases in Ptot, suggesting brain death. In addition, birds presented a shorter latency to cessation of movement after pentobarbital sodium injection compared to MCD and CD (22 vs. 115 s and 136 s, respectively). There were significant increases in F95 and decreases in Ptot at 120 s after application of CD; and a concomitant decrease in the frequency bands at 135 s and isoelectric EEG at 171 ± 15 s. Changes consistent with brain death after MCD included isoelectric EEG at 207 ± 23 s and a significant decreases in some frequency bands at 300 s post-application. No other significant spectrum frequency changes were observed in the MCD group, suggesting brain death likely occurred near the 5-min endpoint. There was no clear association between behavioral, physiological, and EEG responses within CD and MCD treatments. The data demonstrate that pentobarbital sodium induced a rapid death with minimal behavioral and physiological responses regardless of strain of hens. In comparison, use of CD and MCD resulted in a slow onset of brain death in hens.

Efficacy of a Novel Mechanical Cervical Dislocation Device in Comparison to Manual Cervical Dislocation in Layer Chickens

The main objective of this study was to assess the efficacy of mechanical cervical dislocation using the Koechner Euthanasia Device Model C (KED) in comparison to manual cervical dislocation in layer chickens. Laying hens and/or roosters in three different age groups (12, 27-29, and 65-70 weeks old) were randomly assigned to one of three experimental groups: manual cervical dislocation in conscious birds (CD), manual cervical dislocation in anesthetized birds (aCD), or mechanical cervical dislocation by KED in anesthetized birds (aMCD). Anesthetized birds received an intramuscular dose of 0.3 mg/kg medetomidine and 30 mg/kg of ketamine to achieve clinical anesthesia. A comparison of CD vs. aCD responses confirmed that the anesthetic plane abolished or reduced clonic convulsions, nictitating membrane reflex, tonic convulsions, and cloacal relaxation. Time to loss of the pupillary light reflex (~123 s), and time to cardiac arrest (~172 s) were longer (p < 0.001) in the birds in the aMCD group than aCD (~71 and ~137 s, respectively). Radiographs revealed that the majority of the birds killed by manual cervical dislocation (CD + aCD) had dislocations between the skull and atlas (C1) or between cervical vertebrae C1-C2. The KED resulted in a majority of dislocations at C2-C3. Birds killed by manual cervical dislocation presented more subdural and parenchymal hemorrhage in the brain stem compared to birds killed by KED. Radiographs indicated the presence of fractures in a few birds killed by either method (CD + aCD versus aMCD). Compared to manual CD, KED resulted in less brain trauma and a longer latency to brain death, indicating a lower efficacy of KED as an on-farm killing method.

Electroencephalographic, physiologic and behavioural responses during cervical dislocation euthanasia in turkeys

Background

There is a critical need to develop appropriate on-farm euthanasia methods for poultry species. Euthanasia methods should affect the brain first causing insensibility, followed by cardiorespiratory arrest. Neck or cervical dislocation methods, either manual (CD) or mechanical (MCD), are reported to cause a prolonged time to loss of sensibility and death with inconsistent results upon application, especially MCD methods. However, there is limited information on cervical dislocation in turkeys. The overall objective of this study was to assess the welfare implications of CD and a newly developed MCD device for euthanasia of cull turkeys in comparison with intravenous (IV) pentobarbital sodium (1 mL/4.5 kg), the gold standard euthanasia method. Time to death using electroencephalographic (EEG) and behavioural responses were monitored in eight and eighteen week-old turkeys for five minutes after each euthanasia method application. Spectral analyses of EEG responses and onset of isoelectric EEGs were compared to baseline EEG recordings of birds under anesthesia and behavioural responses were studied among euthanasia treatments. A significant decrease in brain activity frequencies analysis and isoelectric EEG were recorded as time of brain death.

Results

All turkeys euthanized with IV pentobarbital sodium presented a rapid and irreversible decrease in the EEG activity at approximately 30s post-injection with minimal behavioural responses. CD and MCD methods caused EEG responses consistent with brain death at approximately 120 s and 300 s, respectively. Additionally, isoelectric EEGs resulted in all pentobarbital sodium and CD groups, but only in 54 and 88% of the eight and eighteen week-old turkeys in the MCD groups, respectively. There were few clear patterns of behavioural responses after CD and MCD application. However, cessation of body movement and time to isoelectric EEG after CD application were positively correlated.

Conclusions

Use of CD and MCD resulted in a prolonged time to death in both age groups of turkeys. MCD application presents a number of welfare risks based on electroencephalographic and behavioural findings. Intravenous pentobarbital sodium induced rapid brain death, but possesses several on-farm limitations. To develop improvements in cervical dislocation methods, further investigations into combined or alternative methods are required to reduce the prolonged time to insensibility and death.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1885-x) contains supplementary material, which is available to authorized users.

Anatomical Pathology, Behavioral, and Physiological Responses Induced by Application of Non-penetrating Captive Bolt Devices in Layer Chickens

We evaluated three models of non-penetrating captive bolt devices, Zephyr-E, Zephyr- EXL, and Turkey euthanasia device (TED) for time to loss of sensibility and degree of brain damage during euthanasia in four age groups of male and female layer chickens (10–11, 20–21, 30–35, 60–70 weeks respectively). Latencies to onset of insensibility and cardiac arrest were assessed to detect whether killing birds via these devices was humane and effective. Both gross and microscopic pathology evaluations were conducted to score skull and brain trauma post mortem. All three NPCB devices induced loss of breathing, pupillary reflex and nictitating membrane reflex within 5 s after application in most chickens. Latencies to loss of jaw tone and neck muscle tone were longer in 60–70 weeks old roosters (p < 0.05). Younger birds (10–21 week-old) demonstrated the longest time (p < 0.0001) to onset of tonic convulsions, time at last movement, cloacal relaxation and cessation of heart beat. A positive correlation (p < 0.0001) was found for all three devices between time of cardiac arrest and times to onset of tonic convulsions, last movement, and cloacal relaxation. More than 80% of birds had skin lacerations with external bleeding following application of all 3 devices. Device type did not affect the incidence of skull fractures but higher skull fracture scores were noted in 10–11 week-old birds compared to other ages. Regardless of device type and age, microscopic SDH was most apparent in the brain and proximal spinal cord of all birds. In summary, all three devices caused significant trauma to the midbrain and spinal cord. Results demonstrated that all three devices induce rapid insensibility after application and can be used as a single-step method that results in a humane death in all age groups of layer chickens.