Assessing unconsciousness in livestock at slaughter

Abstract

Verhoeven, M.T.W. (2016). Assessing unconsciousness in livestock at slaughter. PhD thesis, Wageningen University, The Netherlands Assessing unconsciousness in livestock at different stages of the slaughter process is a legal requirement according to EU legislation. The assessment can be based on absence of readily observable indicators (behavioural indicators, physical signs and reflexes) or, under experimental conditions, by recording and subsequent assessment of brain activity as presented in an electroencephalogram (EEG). There is no consensus, however, to what extent different behavioural indicators, physical signs and reflexes accurately reflect unconsciousness. The aim of this thesis was to study the relationships between these readily observable indicators and EEG activity to provide information on 1. the exact point in time at which animals lose consciousness when subjected to different stunning and slaughter methods and 2. the validity of behavioural indicators, physical signs and reflexes used to assess unconsciousness at slaughter under commercial conditions. The results showed a large variation in time to loss of consciousness, based on EEG activity, both between stunning and slaughter procedures and amongst animals. Captive bolt stunned calves lost consciousness instantly following the stun. Loss of consciousness in pigs during CO 2 stunning varied from 21 to 61 s after start of the exposure. An increased CO 2 concentration decreased the time to loss of consciousness. Times to loss of consciousness in sheep slaughtered without stunning varied from 6 to 24 s. In cattle slaughtered without stunning, times to loss of consciousness varied from 14 s up to over two minutes. Following captive bolt stunning in calves, absence of reflexes indicated unconsciousness. When consciousness was lost gradually (e.g. CO 2 stunning and nonstunned slaughter) none of the readily observable indicators could identify the exact point in time at which animals lost consciousness. Absence of rhythmic breathing, corneal reflex-and eyelid reflex were valid indicators of unconsciousness following CO 2 stunning and non-stunned slaughter, but these indicators were quite conservative as they were initially absent long after EEG activity indicated unconsciousness. When presence of these indicators would require (re)stunning, many animals will have to be (re)stunned. The results also showed that under full commercial conditions, stunning effectiveness must be closely monitored by slaughter plant employees, since risks for stun failures are higher under commercial conditions compared to experimental conditions. CONTENTS

Movements after Captive Bolt Stunning in Cattle and Possible Animal- and Process-Related Impact Factors—A Field Study

“…This is in line with previous studies, such as the work of Fricker and Riek [20], who confirmed that convulsive activity still occurs in cattle with absent brain function (isoelectric EEG). Convulsions result from the failure of higher-level motor control centres in the brain, thus being incompatible with a simultaneously maintained consciousness [18,28,40]. Therefore, the mere presence of movements is not suitable to distinguish between consciousness and unconsciousness [29].…”

“…In studies by Terlouw et al [17], all cattle showed at least one movement after stunning, and post-stun movements by cattle with the spinal cord severed after stunning did not differ from those by cattle on which this manipulation was not performed. Clonic seizures such as reflex-like paddling of the hind limb are signs of a correctly performed bolt stun in cattle [17,18]. This is caused by the lack of inhibition of medullary or spinal reflexes due to the trauma-induced failure of higher-level centres in the brain [19] and also explains the occurrence of the above-mentioned convulsions during a zero-line EEG [20,21].…”

Qualitative welfare risks of cows offered to a Dutch mobile slaughter unit

“…In a later Swedish study, the stun-to-stick interval was 104 seconds for the MSh and 44 seconds at a stationary-but small-scale-slaughterhouse (Hultgren et al, 2018). The stun-to-stick interval should not be longer than 30 s in mechanically stunned animals, in order to ensure that the animal remains unconscious during bleeding [Grandin and Committee 2013in Verhoeven (2016]. In (un-stunned) ritually slaughtered animals, it is not uncommon for blood to enter the airway of the animals.…”

Welfare indicators for stunning versus non‐stunning slaughter in sheep and cattle: A scoping review

“…28,29 EEG or electrocorticographic (ECoG) traces are used experimentally to measure trends in electrical brain activity of anaesthetised animals, which may indicate onset and extent of insensibility following slaughter. 18,30 A universally preferred measurable welfare indicator at slaughter is difficult to establish, leading stakeholders to incorporate the full variety reported across the literature when discussing welfare at slaughter. 4,31 To the authors' knowledge, there does not appear to be a previously published structured review of the literature specifically comparing welfare indicators of sheep and/or cattle measured at both stun and non-stun slaughter.…”

“…Other studies measure observed signs of unconsciousness such as loss of posture, palpebral and corneal reflexes and absence of rhythmic breathing to indicate welfare 28,29 . EEG or electrocorticographic (ECoG) traces are used experimentally to measure trends in electrical brain activity of anaesthetised animals, which may indicate onset and extent of insensibility following slaughter 18,30 . A universally preferred measurable welfare indicator at slaughter is difficult to establish, leading stakeholders to incorporate the full variety reported across the literature when discussing welfare at slaughter 4,31 .…”