Checking the effectiveness of stunning was one of the major tasks when the authors evaluated the stunning process on request of the slaughterhouse managements, retailers or competent authorities in slaughterhouses in Austria, Germany and Switzerland between the years 2000 and 2011. A total of 50 assessments in slaughterhouses for cattle and 116 for pigs were included in this study. For every assessment the technical features of the stunning device, the performance by the personnel and the clinical signs of the animals after stunning were recorded. The assessments of captive-bolt (CB) stunning were made in 1,823 cattle. For pigs, 63 assessments were carried out in electrical stunning (26 in a pen [ESP], 24 in a trap [EST] and 13 in an automatic restrainer [ESR]) and 53 assessments in CO2 stunning, covering a total of 35,220 pigs (6,855 electrically stunned and 28,365 stunned using CO2). The proportions of assessments in which there were no failures were 28% (CB), 12% (ESP), 21% (EST), 31% (ESR) and 13% (CO). The mean percentages of animals showing signs not compatible with sufficient depth of stunning were 13.5 (± 19.0)% (CB), 12.5 (± 16.4)% (ESP), 10.9 (± 11.4)% (EST), 3.2 (± 3.3)% (ESR) and 7.5 (± 13.0)% (CO2) showing a high variability between premises assessed. Stunning effectiveness for cattle was better where a chest stick was performed compared to a neck cut. For pigs, less stunning failures occurred in electrical stunning where the two-cycle method (head/heart current) was applied compared to head-only stunning, and most of the failures in CO2 stunning were due to insufficient dwell time. Reasons for the stunning failures are described and recommendations given to improve the situation.

Efficient stunning is essential for the welfare of animals destined for slaughter. Several studies have dictated certain signs as reliable for the assessment of stunning efficiency in cattle. However, there is still a lack of data concerning the viability of these signs. The aim of the following study was to assess stunning efficiency at a slaughterhouse, studying the relationship between age, sex and breed of cattle and the efficiency of stunning and determining the feasibility of the following signs in assessing stunning efficiency: immediate collapse, muscle spasms, rhythmic breathing, rotation of the eyeballs, painful response to ear or nose pinch, vocalisation and muscle tone of the ears. Cattle were observed immediately after stunning and hoisting onto the bleed rail. Results showed that stunning efficiency decreased with age, was greater in females than males (for animals greater than 12 months of age) and was superior in ‘dairy’ compared to ‘beef’ cattle at all age ranges. Presence of ear muscle tone, absence of muscular spasms, presence of rhythmic breathing, and vocalisation were the most common signs of inefficient stunning recorded in the present study. Recognition of the most frequently occurring signs associated with inefficient stunning will point out the need for re-stunning, preventing animals from regaining sensibility.

Cattle may suffer pain and distress if incorrectly stunned. Regular monitoring of stun quality in abattoirs is now required by EU law. This study aimed to assess stun quality in cattle slaughtered under commercial conditions. A stun protocol was developed to evaluate when inadequate stunning occurred. This included rating of identified symptoms into three levels from highest to lowest risk for inferior animal welfare. Stun to stick interval times, shot accuracy, repeat shots, and stun quality variations between different cattle classes and by different shooters was also investigated. A total of 585 bulls and 413 other cattle classes (306 cows, 58 steers and 49 calves) were studied. Inadequate stunning occurred in 12.5% (16.7% of bulls, compared with 6.5% other cattle). Bulls displayed symptoms rated the highest level for inferior stun quality three times more frequently than other cattle. Despite being shot accurately, 13.6% bulls were inadequately stunned compared with 3.8% other cattle. Twelve percent of cattle were reshot, and 8% were inaccurately shot. Calves were shot inaccurately more frequently (14%) than other cattle. Percentage of cattle shot inaccurately ranged from 19% for the least experienced shooter to 5% for the most experienced. Stun to stick times averaged 105 (± 17) s posing questions for animal welfare, considering the number of cattle inadequately stunned. Stun quality could be improved by using more powerful stunners for shooting bulls, regular servicing of weapons, and use of neck restraints to improve shot accuracy. This study highlights the importance of external monitoring of stun quality at slaughter.