Effect of electrical stunning at slaughter on the quality of farmed turbot (Psetta maxima)

Food quality aspects of farmed turbot (Psetta maxima) were compared following two methods of slaughter: the current commercial method, by immersion in an ice slurry, which is then dewatered after approximately 20 min, or by first humanely, electrically stunning the fish using a prototype commercial stunner, before immersion in an ice slurry, which is dewatered after 20 min. Quality was assessed for up to 10 days of storage on ice following slaughter. No differences were found between the slaughter methods in terms of an overall carcass quality: overall appearance, haemorrhage, damage, burst gall bladder, staining of the body cavity by leakage from the gut or damage to the spine. No detectable difference was found between the treatments using the industry standard freshness scoring system, the Quality Index Method. Both groups of fish were classified as ‘Fresh’ after 10 days of storage on ice. Using objective measurements of colour, no differences between fish from either treatment were found in fillet colour. Changes in flesh pH were similar in electrically stunned and traditionally killed fish with a mean pH (±SE) at 2 h post‐mortem of 6.80±0.027 declining to 6.44±0.032 at 24 h post‐mortem. Humane electrical stunning of turbot at slaughter neither detectably improved nor decreased product quality as measured between 1 and 10 days of storage on ice.     

Field evaluation of live chilling with CO2 on stunning Atlantic salmon (Salmo salar) and the subsequent effect on quality

Atlantic salmon were slaughtered in three ways on a commercial slaughter line: (1) killed by a percussive stun after crowding; (2) killed by percussive stun after crowding, pumping and live chilling; (3) killed by exsanguination after crowding, pumping and live chilling. The live‐chilled fish were exposed to seawater (2°C) saturated with carbon dioxide (pH 5.5–5.7) for 40 min. The fish were calm after live chilling, but not unconscious, as eye rolling was observed in all individuals. Subsequent exsanguination of the unstunned fish resulted in death. Both rapid live chilling and the subsequent exsanguination appeared stressful to the fish, as a large and rapid pH drop coupled with earlier onset of rigor mortis, indicative of high muscle activity during the process were observed. The muscle core temperature during ice storage showed that live chilling only has an effect on carcass temperature during the first 6 h post mortem. After 6 h, no significant differences in temperature were detected between live‐chilled and traditionally ice‐chilled fish. We conclude that commercial use of live chilling in combination with high levels of CO₂ does not stun Atlantic salmon. Live chilling followed by exsanguination of the unstunned fish appears to be highly stressful and should be avoided.     

A feasible method for humane slaughter of eel (Anguilla anguilla L.): electrical stunning in fresh water prior to gutting

It was observed that farmed eels could be rendered unconscious and insensible instantaneously by passing an electrical current through fresh water. The general epileptiform insult on the EEG was characterized by a tonic/clonic and an exhaustion phase. After stunning, the ECG (electro‐cardiogram) revealed fibrillation. The electrical stunning parameters were on average 194 ± 4 V and 0.636 ± 0.040 A/dm² for 1.6 ± 0.4 s. Within a confidence level of 95%%, taking into account the number of animals with a reliable EEG (n = 29), at least 93% of all eels are effectively stunned in fresh water by an average current of 0.636 ± 0.040 A/dm². The behaviour of groups of five eels, which were able to move freely in the water was observed before and after stunning with 50 V and 0.17 A/dm². After 3‐s stunning, two eels were turned upside down. They changed to a normal position after 10 and 13 s respectively. Subsequently, all eels were very active in swimming behaviour and stopped swimming after 75 s. When stunned for a longer duration, all eels were turned upside down and stopped breathing for a limited period of time. In the last experiment the eels were stunned in fresh water (500 μS) with a voltage of 200 V for approximately 1 s, which was followed by 50 V for 5 min. As soon as the stunning started the water was de‐oxygenated by flushing nitrogen to kill the eels by suffocation during the period of unconsciousness and insensitivity. The oxygen saturation decreased from 74 ± 10 to 23 ± 11% at 22 °C. After stunning no brain activity and no responses to pain stimuli were observed on the EEG. The heart rate increased (P < 0.05) after stunning, which was followed by a significant decrease. Only 1 out of 18 eels returned partially from upside down to a normal position 2 h after stunning; however, the eel did not respond to pain stimuli in behaviour. The developed stunning procedure can be recommended for humane slaughter of 50‐kg batches of eels.     

Non‐invasive recording of brain function in rainbow trout: Evaluations of the effects of MS‐222 anaesthesia induction

Effective methods of producing instantaneous and irreversible unconsciousness at the time of slaughter are crucial for ensuring animal welfare in commercial aquaculture. However, the traditional method of visually evaluating unconsciousness has been shown to be insufficient and may lead to misjudgements of stunning efficiency. In this study, we developed a non‐invasive technique that measures brain activity in fish as an alternative to traditional invasive, brain implants and used it to determine when a change in consciousness occurs in trout during anaesthesia induction. Nine rainbow trout (Oncorhynchus mykiss) were equipped with a custom designed silicone cup fitted with electrodes and submerged in 10°C water with dissolved MS‐222. During anaesthesia, the state of consciousness was assessed by recordings of electroencephalogram (EEG). The EEG recordings were analysed both by visually evoked responses from light stimulation (VERs) and from changes in signal amplitude, median frequency and relative signal power. According to the loss of VERs and decrease in signal amplitude, trout transitioned to surgical depth of anaesthesia within 5 min. Our results show that consciousness, or loss of, can be determined using a non‐invasive system to record EEG in fish.     

Comparison of the effects of six stunning/killing procedures on flesh quality of sea bass (Dicentrarchus labrax,Linnaeus 1758) and evaluation of clove oil anaesthesia followed by chilling on ice/water slurry for potential implementation in aquaculture

The effects of different stunning/killing procedures on flesh quality of European sea bass were investigated: (1) anaesthesia with clove oil, (2) anaesthesia with 2‐phenoxyethanol, (3) percussive stunning, (4) immersion in ice/water slurry, (5) chilling on ice and (6) anaesthesia with clove oil followed by immersion in ice/water slurry. Muscle pH values were significantly lower in sea bass anaesthetized or stunned by a blow to the head compared with fish immersed in ice/water slurry, chilled on ice or immersed in ice/water slurry after clove oil anaesthesia. Lightness was highest in sea bass anaesthetized by 2‐phenoxyethanol or percussively stunned and lowest in ice‐chilled fish. Redness and yellowness were highest in fish chilled on ice and lowest in fish anaesthetized with clove oil. Liquid loss, fat loss and shear values were not significantly different among the procedures. In general, lipid oxidation values during refrigerated or frozen storage did not significantly differ among treatment groups. Combination of clove oil anaesthesia followed by chilling on ice/water slurry appears to improve both flesh quality and welfare of sea bass, although the implementation of further studies is warranted to consolidate this finding.     

Relevance of age at slaughter on meat quality of turkeys stunned with CO2

1. The objective of this work was to determine the effect of slaughter age and stunning method on the quality of turkey meat from poultry processing plants.

2. One hundred B.U.T. Premium turkeys were divided into 4 groups of 25 animals according to slaughter age (15 or 17 weeks) and CO₂ stunning procedure (G1 stepwise: step1: 30% CO₂, 15 s; step 2: 55% CO₂, 40 s; step 3: 70% CO₂, 45 s; G2: progressive increase of the CO₂ concentration at a rate of 0.8% per s for 100 s). The quality of the breast meat was determined in fillets taken at different post-mortem times.

3. There were differences between the stunning groups for several variables (pH: 6.01 ± 0.01 and 5.95 ± 0.02; a*: ?1.84 ± 0.05 and ?2.21 ± 0.04; b*: 4.99 ± 0.15 and 4.68 ± 0.16; drip loss: 0.85 ± 0.02 and 0.71 ± 0.02 for G1 and G2, respectively), while no significant differences were found for L*, cooking loss and texture analysed with a Warner Bratzler Shear Force cell (WBSF).

4. Slaughter age had a significant effect on all the parameters studied (pH: 6.01 ± 0.01 and 5.95 ± 0.01; a*: ?2.21 ± 0.05 and ?1.88 ± 0.05, b*: 5.50 ± 0.17 and 4.42 ± 0.15; drip loss: 0.71 ± 0.02 and 0.86 ± 0.02, cooking loss: 12.56 ± 0.22 and 14.69 ± 0.16 for turkeys slaughtered at 15 and 17 w, respectively) except on L* and WBSF.

5. The ageing of the meat affected pH, colour values, drip loss and WBSF, with differing degrees of evolution: mean values of L* (39.36 ± 0.35. 45.77 ± 0.20 and 46.30 ± 0.24, for 20 min, 24 h and 7 d post mortem, respectively) and drip loss (0.75 ± 0.03 and 0.84 ± 0.02 for 24 h and 7 d post mortem, respectively) increased, those of a* (?1.77 ± 0.08, ?1.94 ± 0.07 and ?2.22 ± 0.05 for 20 min, 24 h and 7 d post mortem, respectively) and WBSF decreased (3.73 ± 0.06 and 2.63 ± 0.04 for 24 h and 7 d post mortem, respectively), those of pH decreased in the first 24 h and remained stable for the next 6 d (6.19 ± 0.02, 5.87 ± 0.01 and 5.88 ± 0.01), and those of b* increased in the first 24 h post-mortem and remained stable for the next 6 d (3.26 ± 0.31, 5.86 ± 0.16 and 5.47 ± 0.08).

6. The results revealed no critical differences between stunning methods, and suggest that animals slaughtered at 15 weeks present higher quality meat than those slaughtered at 17 weeks.     

The occurrence of reflexes and reactions in cattle following stunning with a captive bolt at the slaughterhouse

The difference in the frequency of the occurrence of reflexes/reactions in 355 cows (average weight 505.5 ± 7.9 kg) and 262 bulls (average weight 735.6 ± 8.4 kg) following stunning with a Matador SS 3,000 B trigger‐activated captive bolt gun (Termet) was determined. The stun shot more than 2 cm from the ideal position was found in 79.6% of animals. Vocalization, corneal reflex, rhythmic breathing, blinking, eyeball rotation and the absence of tongue protrusion occurred more frequently in bulls (p < .05). Spontaneous limb movements and nystagmus occurred more frequently in cows (p < .05). No difference between bulls and cows was determined in the occurrence of a response to painful stimuli or attempts to regain normal posture. No dependency was determined between the frequency of the occurrence of a reflex/reaction and the distance of the stun shot from the ideal point on the skull for any of the monitored signs. This study shows that the occurrence of reflexes/reactions following the stunning of cattle with a captive bolt is not only dependent on the position of the shot if placed within a 9 cm radius from the ideal point on the cattle skull.     

宿根矮化病菌的竞争定量PCR检测方法建立

利用宿根矮化病菌的特异检测引物,构建竞争定量PCR检测的非同源模板,建立宿根矮化病菌的竞争定量PCR检测方法.实验中非同源模板(竞争模板)构建是采用PCR方法对大肠杆菌基因组进行低严谨度扩增,回收合适的DNA片段并将其构建到T-esay载体上,通过测序和序列比对,除两端引物序列完全相似外,其余部分没有同源性,因此可以作为定量检测的非同源模板.通过计算非同源模板的拷贝数,进行竞争定量PCR检测宿根矮化病,建立宿根矮化病菌的标准竞争曲线和直线回归方程.本研究建立的竞争定量PCR检测方法操作简单、特异性和敏感性高,适合于宿根矮化病菌的检测,并可为其它病菌竞争定量PCR检测方法的建立提供参考.     

屠宰前不同二氧化碳浓度的混合气体致晕对肉鹅肝脏颜色、脂质氧化及抗氧化能力的影响

本试验旨在研究屠宰前不同二氧化碳(CO_2)浓度的混合气体致晕(控制气体击晕)对肉鹅肝脏颜色、脂质氧化及抗氧化能力的影响。试验选取56只85日龄的扬州鹅公鹅,随机分成7个组(1个对照组,6个试验组),每组8个重复,每个重复1只。对照组不致晕直接屠宰,试验组屠宰前由不同CO_2浓度的混合气体致晕。6个试验组致晕混合气体组成如下:G40组,40%CO_2+21%氧气(O_2)+39%氮气(N_2); G50组,50%CO_2+21%O_2+29%N_2; G60组,60%CO_2+21%O_2+19%N_2; G70组,70%CO_2+21%O_2+9%N_2; G79组,79%CO_2+21%O_2。上述5组致晕时间均为7 min。G40+G79组,40%CO_2+30%O_2+30%N_2致晕2 min,然后79%CO_2+21%O_2致晕5 min。结果显示:G79组肉鹅的放血率最低,与对照、G40、G50、G70和G40+G79组均存在显著差异(P<0.05)。G40组肝脏在屠宰后1和4 d的亮度值及在屠宰后1 d的黄度值均显著高于G79和G40+G79组(P<0.05)。屠宰后1 d,G40组肝脏中丙二醛(MDA)含量显著低于G70和G79组(P<0.05);屠宰后4和7 d,G79组肝脏中MDA含量显著低于G40组(P<0.05)。屠宰后0 d,G79组肝脏1,1-二苯基-2-三硝基苯肼(DPPH)自由基清除能力最低,G40组最高,但组间差异不显著(P>0.05)。屠宰后1、4和7 d,G40组肝脏中谷胱甘肽过氧化物酶(GSH-Px)活性均显著低于G79组(P<0.05)。屠宰后4 d,G40组肝脏中总超氧化物歧化酶(T-SOD)活性显著高于G79组(P<0.05)。综上所述,肉鹅屠宰前采用40%CO_2混合气体(40%CO_2+21%O_2+39%N_2)致晕可以改善肝脏颜色,且在短期(0～1 d)内肝脏DPPH自由基清除能力最高,脂质氧化程度较低,而高浓度(79%) CO_2混合气体(79%CO_2+21%O_2)致晕可以缓解中长期(4～7 d)储存时肝脏的脂质氧化。