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Simple Summary: Stunning during the slaughter process consists of inducing unconsciousness in animals in order to prevent them from feeling any avoidable pain, distress, or suffering during bleeding and related operations. In an unconscious state, the animal is unable to perceive and respond to any external stimuli, including pain. Currently, the two main stunning methods used commercially in broiler chickens are the electrical waterbath and carbon dioxide in two phases. Although the latter is widely recommended over electrical waterbath stunning, it is still not devoid of risks for animal welfare. For instance, the induction to unconsciousness is not immediate and involves a transitional period during which aversion to the inhalation of carbon dioxide might occur. The present study demonstrates that mixtures of carbon dioxide with nitrogen improve a broiler chicken's welfare during stunning since they result in a more rapid induction of unconsciousness and reduce the aversion experienced, compared to carbon dioxide in two phases, in broiler chickens. This study evaluated the exposure to gas mixtures of carbon dioxide (CO2) associated with nitrogen (N2) as alternatives to CO2 in two phases to improve the welfare of broiler chickens at slaughter. Broilers were exposed to one of three treatments: 40C90C (1st phase: <40% CO2 for 2 min; 2nd phase: >90% CO2 and <2% O2 for 2 min, n = 92), 40C60N (40% CO2, 60% N2, and <2% O2 for 4 min, n = 79), or 20C80N (20% CO2, 80% N2, and <2% O2 for 4 min, n = 72). Brain activity (EEG) was assessed to determine the onset of loss of consciousness (LOC) and death. Behavioural assessment allowed for characterisation of an aversive response to the treatments and confirmed loss of posture (LOP) and motionlessness as behavioural proxies of LOC and brain death in 40C60N and 20N80C. However, the lack of quality of the EEG traces obtained in 40C90C did not allow us to determine the onset of LOC and brain death for this treatment. The onset of LOC in 40C60N was found at 19 s [14–30 s] and in 20C80N at 21 s [16–37 s], whereas a LOP was seen at 53 s [26–156 s] in 40C90C. Birds showed brain death in 40C60N at 64 s [43–108 s] and in 20C80N at 70 s [45–88 s]), while they became motionless in 40C90C at 177 s [89–212 s]. The 40C90C birds not only experienced more events of aversive behaviours related to mucosal irritation, dyspnoea, and breathlessness during induction to unconsciousness but were at risk of remaining conscious when the CO2 concentration was increased in the 2nd phase (known to cause severe pain). From an animal welfare point of view, 40C60N proved to be the least aversive of the three treatments tested, followed by 20C80N and 40C90C. [ABSTRACT FROM AUTHOR]

ABSTRACT: Increased consumer concern for animal welfare has led some poultry producers to alter their stunning methods from electrical to controlled atmosphere stunning. The potential for different impacts on meat quality between commercially applied controlled atmosphere stunning (CAS) and electrical stunning (ES) using current US parameters needs further evaluation. Three trials were conducted in a commercial broiler processing facility that uses separate processing lines for ES and CAS. Blood glucose concentrations were measured from broilers stunned by either CAS or ES at: 1) lairage, 2) pre-stunning, and 3) post-stunning, using a glucose monitor. Occurrence of visible wing damage was evaluated post-defeathering and breast fillet meat quality was evaluated through measurement of pH, color, and drip loss at deboning and after 24 h. Data were analyzed using GLM or chi-square with a significance at P ≤ 0.05 and means were separated by Tukey's HSD. Blood glucose concentrations (mg/dL) from CAS and ES birds were not different at lairage (284, 272, P = 0.2646) or immediately prior to stunning (274, 283, P = 0.6425). Following stunning and neck cut, circulating blood glucose from birds stunned by CAS was higher than ES (418, 259, P < 0.0001). CAS carcasses had more visible wing damage than ES carcasses (3.6%, 2.2%, P < 0.0001). Breast fillet pH was lower, L* was higher, and a* was lower at debone for CAS fillets (5.81, 54.65, 1.96) compared to ES fillets (5.92, 53.15, 2.31, P < 0.0001, P = 0.0005, P = 0.0303). Drip loss did not differ between breast fillets from CAS or ES broilers (4.83, 4.84; P = 0.0859). The implications of increased blood glucose concentration post-CAS are unknown and require further evaluation. However, the increase in visible wing damage observed post-defeathering from CAS carcasses indicated a need for equipment parameter adjustments during the process from stunning through defeathering when using CAS for broiler stunning. Although differences were observed in breast fillet attributes at deboning, these differences would have minimal practical application and were no longer present at 24 h. Overall, use of CAS in a commercial facility resulted in differences in subsequent product quality when compared to ES.

ABSTRACT: To be compliant with religious requirements for poultry, slaughter facilities using controlled atmosphere stunning may require a reliable method for detecting signs of life. However, the production setting challenges methods utilized in veterinary and field use by generating excess sound and vibration, which can impact the effectiveness of typical measurement tools, such as the stethoscope or doppler ultrasound. In addition, it is required that the process be quick and efficient as to not interfere with the rapid pace of production. The current study assessed various methods including reflexes (pupillary light reflex, nictitating membrane reflex, and pedal reflex), doppler ultrasound, stethoscopes, and pulse oximeter for determination of signs of life in broiler chickens postcontrolled atmosphere stunning in production. Data were analyzed using a generalized linear mixed model in SAS. Each bird was considered an experimental unit (n = 18) and differences between dead on arrival (DOA; n = 6), stunned (n = 10) and sensible (n = 2) birds were compared using contrast statements. Reflexes were seen only in sensible birds. Of the evaluated tools, only the pulse oximeter was consistently capable of detecting heart beats per minute (bpm) within the production environment. Although the values of bpm did not differ between sensible and stunned birds (P = 0.724), DOA birds had a lower bpm than all others (P < 0.001). Although the accuracy of results deserves further investigation and the small sample size of this study posed challenges to our statistical analyses, including low statistical power for the comparison between sensible and stunned groups, the achieved results suggest that the pulse oximeter meets the requirements for a reliable and practical method in detecting signs of life in broilers. With the increasing importance of halal products in a market that prioritizes animal welfare, our results present a promising approach to meet halal certification requirements. Further studies on this topic are strongly encouraged.

Abstract Background Meat color and lipid peroxidation are important traits related to meat quality. CO2 concentration is a critical factor that can affect meat quality in the commercial use of gas stunning (GS). However, the effect and mechanism of CO2 stunning on meat color and lipid peroxidation during long-term storage remain poorly studied. We aimed to study the effects of GS methods, especially CO2 concentration, on meat color and meat lipid peroxidation in broilers during long-term storage at 4 °C and to explore the potential mechanism of meat color change via lipid peroxidation and the inner lipid peroxide scavenging system. Methods Eighteen broilers were sacrificed after exposure to one of the following gas mixtures for 90 s: 40% CO2 + 21% O2 + 39% N2 (G40%), 79% CO2 + 21% O2 (G79%), or no stunning (0% CO2, control). Meat color, serum variables, enzyme activities, and the gene expression of mitogen-activated protein kinase (MAPK), nuclear factor-erythroid 2-related factor 2 (Nrf2), glutathione S-transferase (GST) and superoxide dismutase (SOD) were determined. Results The concentrations of serum triiodothyronine (T3, P = 0.03) and the ratio of serum free triiodothyronine/free thyroxine (FT3/FT4, P

In this study, the simulated hock flexion resistance at which employees could consistently differentiate a stunned bird from a recently dead end-of-lay hen was evaluated. A mechanical apparatus was used with individually weighted levers, ranging in resistance from 66 to 485 gram-force (gf), in a random order. A reference lever was weighted at 120 gf, which is similar to that of stunned birds measured immediately after gas stunning. Each employee (n = 15) lifted each lever to an approximately horizontal plane and designated it as having less resistance or similar resistance to the reference lever (light) or greater resistance than the reference lever (heavy). Dominant and non-dominant hands were tested independently. For resistance of up to 300 gf, there was a significant (P ≤ 0.05) increasing curvilinear trend in the proportion of employees who considered the lever to be heavy, and a significant decreasing curvilinear trend in the proportion who considered the lever to be light. At greater than 300 gf, close to 100% of employees gave the designation heavy, and there was no significant (P > 0.05) change with any further increases in weight. It was concluded that employees could reliably detect hock flexion resistances of ≥300 gf as larger in magnitude than 120 gf. [ABSTRACT FROM AUTHOR]

This study of end-of-lay fowl characterized the development of rigor mortis over time after euthanasia by testing the force required to flex a hock joint and by evaluating wing position as a test to differentiate euthanized birds from stunned birds. Using a force gauge, it was demonstrated that measurable resistance to hock flexion to the point of activation of the perch reflex develops rapidly after death and consistently increases over time, plateauing at 90 min. Based on a minimum detection threshold of 300 gram-force (gf) for hock stiffness, birds that developed rigor quickly, in the 50th percentile and higher, were detectable by 5min postmortem, and all birds in the study population were detectable by 21 min postmortem. In addition, the sensitivity and specificity of wing position to differentiate dead birds from stunned birds was high (87.5 and 100%, respectively). We conclude that the development of palpable hock joint stiffness is sufficiently rapid to be useful as ameans of differentiating between hens unconscious after CO2 gas stunning from hens that died during transport or lairage. Wing position can be used as a secondary assessment as the hen is lifted to the shackle line, such that the presence of wings held tight to the body would identify the hen as a DOA. [ABSTRACT FROM AUTHOR]

This study examined the welfare implications of euthanizing broilers with 3 gas mixtures relevant to the commercial application of controlled atmosphere stunning (GAS). Birds were implanted/equipped with electrodes to measure brain activity (electroencephalogram, EEG) and heart rate. These signals were recorded using a purpose-built telemetry-logging system, small enough to be worn by each bird in a spanclex backpack. The birds were euthanized in a scaled-down GAS apparatus consisting of a conveyor belt passing through 2 compartments. Three gas environments were applied (8 birds per treatment): 1) anoxia (N2 with <2% residual O2, in both compartments), 2) hypercapnic anoxia (N2 with 30% CO2 and <2% residual O2, in both compartments), and 3) a 2-phase approach with a hypercapnic hyperoxygenated anesthetic phase (40% GO2, 30% O2, and 30% N2, in the first compartment, 80 s) followed by a second euthanasia phase (80% CO2 in air, in the second compartment). All 3 GAS approaches effectively achieved nonrecovery states, and time to loss of consciousness for each bird was determined by visual determination of isoelectric EEG and by calculation of the correlation dimension of the EEG. Hypercapnic anoxia resulted in rapid unconsciousness and death; both anoxic treatments were associated with early onset prolonged wing flapping and sustained tonic convulsions as displayed in the electiophysiological recordings. These responses were seen in the period when consciousness remained a possibility. Hypercapnic hyperoxygenation (the 2-phase approach) was associated with respiratory disruption, but this treatment eliminated initial clonic convulsions in the stunning process, and tonic convulsions were not seen. These results suggest that the presence of O2 in the first stage of CAS is associated with an absence of potentially distressing behavioral responses. The respiratory discomfort associated with hypercapnic hyperoxygenation is an issue. We propose that this may be compensated by a more gradual induction to unconsciousness, which eliminates the impact of other potentially negative experiences. [ABSTRACT FROM AUTHOR]

Background: Meat color and lipid peroxidation are important traits related to meat quality. CO2 concentration is a critical factor that can affect meat quality in the commercial use of gas stunning (GS). However, the effect and mechanism of CO2 stunning on meat color and lipid peroxidation during long-term storage remain poorly studied. We aimed to study the effects of GS methods, especially CO2 concentration, on meat color and meat lipid peroxidation in broilers during long-term storage at 4 °C and to explore the potential mechanism of meat color change via lipid peroxidation and the inner lipid peroxide scavenging system. Methods: Eighteen broilers were sacrificed after exposure to one of the following gas mixtures for 90 s: 40% CO2 + 21% O2 + 39% N2 (G40%), 79% CO2 + 21% O2 (G79%), or no stunning (0% CO2, control). Meat color, serum variables, enzyme activities, and the gene expression of mitogen-activated protein kinase (MAPK), nuclear factor-erythroid 2-related factor 2 (Nrf2), glutathione S-transferase (GST) and superoxide dismutase (SOD) were determined. Results: The concentrations of serum triiodothyronine (T3, P = 0.03) and the ratio of serum free triiodothyronine/free thyroxine (FT3/FT4, P < 0.01) were decreased, whereas levels of serum cortisol (P < 0.01) were increased in the 40% CO2 group compared with the control group. Additionally, the thiobarbituric acid-reactive substances (TBARS) 3 d (P < 0.01) and TBARS 6 d (P = 0.01) in breast meat and the TBARS 3 d in thigh meat (P < 0.01) were increased in the 40% CO2 group compared with the control group. Serum T3 was negatively correlated with TBARS6 d both in the breast and thigh meat (r = − 0.63, P < 0.01 and r = − 0.47, P = 0.05 respectively). T3/T4 was negatively correlated with TBARS6 d in the breast meat and in the thigh meat (r = − 0.57, P = 0.01; and r = − 0.53, P = 0.03 respectively). Compared with the control group, Lightness (L*) 1 d (P = 0.03) and L*9 d (P < 0.01) were increased, whereas total chromatic aberration (E*) 1 d (P = 0.05) and E*3 d (P < 0.01) were decreased in the breast meat of both the G40% and G79% groups. The values of yellowness (b*) 3 d (P = 0.01), b*6 d (P < 0.01) and E*6 d (P < 0.01) in the thigh meat were lower in both the G40% and G79% groups than in the control group. In the breast muscle, the mRNA levels of c-Jun N-terminal kinase 2 (JNK2, P = 0.03), GSTT1 (P = 0.04), and SOD1 (P = 0.05) were decreased, and the mRNA levels of JNK1 (P = 0.07), Nrf2 (P = 0.09), and GSTA3 (P = 0.06) were slightly lower in both the G40% and G79% groups compared with the control group. However, among these genes, only the mRNA level of JNK1 was decreased in the G40% group compared with the control group and the G79% group (P = 0.03) in the thigh muscle. Conclusions: Compared with the control group, meat color quality in the breast meat was decreased, and the expression of genes in the MAPK/Nrf2/ARE (antioxidant responsive element) antioxidant pathway in breast muscle was partly suppressed by GS of both 40% and 79% CO2. However, oxidative stress and meat lipid peroxidation during storage were aggravated by GS with 40% CO2 compared to GS with 79% CO2 and no GS. [ABSTRACT FROM AUTHOR]