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Applied Animal Behaviour Science 67 2000 67–76 www.elsevier.comrlocaterapplanim
The aversiveness of carbon dioxide stunning in pigs and a comparison of the CO stunner crate vs. the
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V-restrainer
E.C. Jongman , J.L. Barnett, P.H. Hemsworth
Animal Welfare Centre, Victorian Institute of Animal Science, Sneydes Road, PriÕate Bag 7, Werribee, Victoria 3030, Australia
Accepted 20 October 1999
Abstract
Using aversion learning techniques, the relative aversiveness of CO to pigs in comparison to a
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shock with an electric prodder, and the aversiveness of a CO -stunner crate in comparison to the
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aversiveness of a V-belt restrainer used for electric stunning were examined. The results showed that 90 CO was considerably less aversive than an electric shock with a prodder. However,
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during exposure to 90 CO all pigs lost conscious, which may have affected their memory of the
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procedure. The pigs remained conscious after exposure to 60 CO and again showed virtually
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no aversion towards the stunner crate, while an electric shock with a prodder appeared highly aversive. The aversion to the V-restrainer belt and the CO crate were similar. q 2000 Published
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by Elsevier Science B.V. All rights reserved.
Keywords: Pigs; Stunning; Carbon dioxide; Slaughturestraint; Aversion testing
1. Introduction
Carbon dioxide stunning of pigs is widely used in Europe and America, however, there are still some concerns about the effects on animal welfare. Of particular concern
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are the pungent nature of CO gas Gregory et al., 1990 and the variation in responses
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between pig genotypes to CO stunning Grandin, 1988 . Carbon dioxide is an unpleas-
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ant gas to inhale at high concentrations for humans because of its pungency and the
Corresponding author. Tel.: q61-3-9742-0468; fax: q61-3-9742-0400. Ž
. E-mail address: ellen.jongmannre.vic.gov.au E.C. Jongman .
0168-1591r00r - see front matter q 2000 Published by Elsevier Science B.V. All rights reserved. Ž
. PII: S 0 1 6 8 - 1 5 9 1 9 9 0 0 1 0 3 - 3
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induction of breathlessness Gregory et al., 1990 . Raj and Gregory 1995 found that a majority of pigs showed a strong aversion to 90 of CO . After 24 h of fasting,
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pigs refused to enter an atmosphere of 90 CO for a food reward. Exposing pigs to
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15–20 s of a 70 mixture of CO in air produced an excitation phase with movements
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which resemble escape behaviour and this response has been considered unacceptable Ž
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. Grandin, 1988; Gregory et al., 1990 . However, research by Forslid 1987 and Troeger
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and Woltersdorf 1991 based on electroencephalogram recordings indicates that the animal is unconscious before reaching this phase of behaviour. Induction of uncon-
sciousness prior to the excitatory response should reduce the concern for the welfare of CO -stunned pigs, although there could still be a window of time between unconscious-
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ness and insensibility to pain. Exposure to CO is only one aspect of the slaughtering process. In fact, a number of
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components of the slaughter process may contribute to concern for animal welfare. Aspects of this process that pigs may find unpleasant or aversive and that potentially
impact on welfare include lairage systems and handling systems. Delivery to the CO
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stunner is often through a raceway at ground level, where pigs enter a well-lit crate, sometimes in small groups. This is different to most electrical stunning systems, where
pigs enter a V-restrainer belt. Aversive handling systems can contribute to acute stress Ž
. prior to slaughter as well as affecting meat quality D’Souza et al., 1998 . Therefore, it
is important when studying effects of stunning methods on welfare and meat quality, to study the differences in aversiveness of the components of the slaughter process such as
handling systems associated with the stunning unit.
Ž . The objectives of this study were 1 to examine the relative aversiveness of CO to
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Ž . pigs and 2 to compare the aversiveness of a CO stunner crate to the aversiveness of a
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V-belt restrainer used for electrical stunning.
2. Materials and methods
