Influence of CO2 stunning on EEG, catecholamines and clinical reflexes of slaughter pigs
JÖRG HARTUNG1, THEDA VON MÜFFLING2, BERNHARD NOWAK2
Institut for Animal Hygiene, Animal Welfare and Behaviour of Farm Animals, Bünteweg 17p, 30559 Hannover
Institute for Food Quality and Safety, Bischofsholer Damm 15, 30173 Hannover
University of Veterinary Medicine Hannover, Foundation, Germany, firstname.lastname@example.org
Introduction atmosphere of 90 vol. % CO2 compared to 80 vol.
Approximately 240 million pigs are slaughtered in %.
the EU countries per year. Slaughter is bleeding of
an animal to induce death after stunning. This is a Discussion and Conclusions
statutory requirement. The most common stunning A concentration of at least 90 vol. % CO2 should be
methods use electricity or carbon dioxide (CO2). applied when stunning pigs for slaughter. It seems
Since CO2 stunning requires less handling of the necessary to look in greater detail in the effects of
animals and usually allows stunning of more CO2 stunning on the well-being of pigs. It is to
animals per hour than electrical stunning, it has consider whether pre-stunning using an anaesthetic
become quite popular in many countries. The EU gas should be applied in order to avoid or reduce
directive 93/119/EC permits stunning with an suffering of the animals in the initial phase when
atmosphere containing at least 70% CO2 by volume exposed to the CO2 atmosphere. Proper stunning
in air for a minimum of 70 s, in Germany the law will also improve meat quality.
requires at least 80% CO2. However, there are
observations that after stunning with 80% CO2 for References
70 s some animals still show signs of consciousness Anonymous (1993). Council Directive on the
before exsanguination. Therefore experiments were protection of animals at the time of slaughter or
carried out to measure pig responses to CO2 killing.
atmospheres of both 80% and 90%. EFSA (2004): Report on welfare aspects of animal
stunning and killing methods.
Materials and Methods Hartung, J. et al. (1997). Dtsch. Tierärztl. Wschr.
A total of 460 pigs were stunned with CO2 in a 104, 66-68.
German slaughterhouse with a one-gondola dip-lift Hartung, J.et al. (2002). Dtsch. Tierärztl. Wschr.
system. The animals were immediately brought into 109, 135-139.
the CO2 atmosphere at maximum concentration. Raj, M. (1999). Vet. Rec. 144, 165-168.
The floor of the gondola reached the bottom of the Troeger, K., Woltersdorf (1991). Fleischwirtschaft
pit in 22 s and returned to the ejection level 25 s 71, 1063-1068.
later. Investigations were carried out during the Velarde, A. et al. (2000). Vet. Rec. 146, 65-68.
normal slaughter routine. The response of the pigs
to CO2 such as catecholamines (adrenalin, AD, nor-
adrenalin, NAD) and lactate in the blood as well as Tab. 1: Clinical reflexes
clinical reactions (nasal septum and corneal reflex, directly during
heart rate) were investigated. Special EEG- after tip-out de-bleeding
electrodes were adapted on some pigs for the
CR NR HB CR NR HB
measurement with a mobile data logger. The CO2 - -
concentrations were measured continuously close to 80 Vol. % CO2 + + + +
- - - - - -
the head of the pigs when transported up and down 90 Vol. % CO2
in the stunning gondola. CR: corneal reflex; NR: nose reflex; HB: heart beat
+ = present
Results - = absent
The results show that the exposure of pigs to a CO2
atmosphere of 80 vol. % for 70 s is not sufficient
for a proper stun. A number of animals still showed
typical reactions in the EEG (delta activities). Tab. 2: Catecholamines and lactate in blood plasma
Clinical reflexes were seen regularly during de- of pigs before and after CO2-stunning
bleeding (Tab. 1). When 90 vol. % CO2 is applied, before stunning in sticking blood
most animals seem to be already dead before de- Ad Nad La Ad Nad La
bleeding starts. This may create concerns in regard (ng/l) (ng/l) (mmol/l) (ng/l) (ng/l) (mmol/l)
to meat hygiene. In the sticking blood very high 80 Vol% CO2 90 320 1.4 131400 252600 10.8
concentrations of catecholamines were found after 90 Vol% CO2 146 395 1.2 112.600 228100 7.1
both applications (80 and 90 vol. % CO2) which Ad: adrenalin; Nad: noradrenalin; La: lactate
were 1000 times higher than in the same pigs
waiting in the lairage (Tab. 2). These values are
even 10 times higher than after electrical stunning.
Lactate levels are lower after exposure to an