Stunning pigs with nitrogen and carbon dioxide mixtures: Effects on animal welfare and meat quality

P. Llonch, P. Rodríguez, M. Gispert, A. Dalmau, X. Manteca, A. Velarde

Research output: Contribution to journalArticleResearchpeer-review

18 Citations (Scopus)


The aim of this study was to assess the effect of exposure to the gas mixtures of 70% nitrogen (N 2) and 30% carbon dioxide (CO 2; 70N30C), 80% N 2 and 20% CO 2 (80N20C) and 85% N 2 and 15% CO 2 (85N15C) on aversion, stunning effectiveness and carcass, as well as meat quality in pigs, and to compare them with the commercial stunning of 90% CO 2 (90C). A total of 68 female pigs were divided into four groups and stunned with one of the gas mixtures. During the exposure to the gas, behavioural variables (retreat attempts, escape attempts, gasping, loss of balance, muscular excitation and vocalizations) were recorded, and at the end of the stunning, corneal reflex and rhythmic breathing were assessed. After slaughter, meat quality parameters such as pH at 45 min post mortem (pH45) and at 24 h post mortem (pHu), electrical conductivity, drip loss and colour, in the Longissimus thoracis (LT) and Semimembranosus (SM) muscles were measured, and the presence of ecchymosis on the hams was noted. The PROC MIXED and the PROC GENMOD of SAS® were used to analyse the parametric and binomial variables, respectively. The 'gas mixture' was always considered a fixed effect and the 'live weight' as a covariate. To assess the correlation between meat quality and behaviour measures, PROC CORR was used. Pigs exposed to 90C showed a higher percentage of escape attempts and gasping, a lower percentage of vocalization and shorter muscular excitation phase than pigs exposed to the other N 2 and CO 2 mixtures (P < 0.05). After stunning, no pig exposed to 90C showed corneal reflex or rhythmic breathing, whereas 85% and 92% of the animals exposed to N 2 and CO 2 mixtures showed corneal reflex and rhythmic breathing, respectively. Animals stunned with 80N20C and 85N15C had a lower pH45 (P < 0.01) than animals exposed to 90C. Electrical conductivity in the SM muscle was lower (P < 0.001) in 90C and 70N30C pigs than in 80N20C and 85N15C pigs, whereas in LT, it was lower (P < 0.05) in 90C pigs than in 85N15C. As the CO 2 concentration of the gas mixture was decreased, the prevalence of exudative pork increased. Twenty-five percent of animals exposed to N 2 and CO 2 mixtures (n = 68) had ecchymosis in their carcasses, whereas no animal stunned with 90C had ecchymosis. In conclusion, although N 2 and CO 2 stunning exhibit fewer signs of aversion than 90C, their induction time to unconsciousness is longer, and this may negatively affect meat and carcass quality. © 2011 The Animal Consortium.
Original languageEnglish
Pages (from-to)668-675
Issue number4
Publication statusPublished - 1 Apr 2012


  • aversion
  • meat quality
  • nitrogen
  • pigs
  • stunning


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