Use of high concentrations of carbon dioxide for stunning rabbits reared for meat production


  • A. Dalmau Animal Welfare Unit. IRTA
  • J. Pallisera Animal Welfare Unit. IRTA
  • C. Pedernera Animal Welfare Unit. IRTA
  • I. Muñoz Food Technology Unit. IRTA.
  • R. Carreras Animal Welfare Unit. IRTA
  • N. Casal Animal Welfare Unit. IRTA
  • E. Mainau Animal Welfare Unit. IRTA
  • P. Rodriguez Animal Welfare Unit. IRTA
  • A. Velarde Animal Welfare Unit. IRTA



animal welfare, aversion, behaviour, CO2, rabbits, stunning


Abstract: An investigation was performed to determine whether high concentrations of carbon dioxide (CO2) at 70-98% in atmospheric air are a suitable alternative for stunning rabbits compared to conventional approaches such as electronarcosis. Aversion to the gas and efficacy in causing prolonged unconsciousness and death were studied in a total of 480 rabbits by means of behavioural parameters, physiological indicators (presence of rhythmic breathing and corneal reflex) and electroencephalography (EEG, brain function). The use of any of the 4 studied concentrations of the gas caused more nasal discomfort and vocalisations than the use of atmospheric air (P<0.001). EEG activity confirmed that loss of posture is a good indicator of the onset of unconsciousness in rabbits exposed to CO2, occurring earlier (P<0.05) at 90 and 98% than at 70 and 80%. Rabbits showed signs of aversion for 15 s before the onset of unconsciousness, which occurred around 30 s after the beginning of the exposure to the gas, similar to species such as swine in which high concentrations of CO2 are also used for stunning. CO2 at 80 to 98% is suggested as a reasonable concentration range to induce a long state of unconsciousness and death in rabbits, while 70% CO2 is not recommended because it requires too long duration of exposure (more than 360 s) to ensure effectiveness. Despite the advantages in terms of pre-stun handling and irreversibility, CO2 is not free of animal welfare concerns. In consequence, a debate is necessary to ascertain if CO2 can be considered a suitable alternative to stun rabbits, considering the advantages and drawbacks cited, quantified in the present study as 15 s of aversion (nasal discomfort and vocalisations) before losing posture.


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Anil M.H., McKinstry J.L. 1991. Reflexes and loss of sensibility following head-to-back electrical stunning in sheep. Vet. Rec., 128: 106-107. doi:10.1136/vr.128.5.106

Bradley Bays T., Lightfoot T., Mayer J. 2006. Exotic pet behaviour: Birds, Reptiles and Mammals. Philadelphia: Saunders.

Cameron A.C., Trivedi P.K. 1998. Regression analysis of count data. Cambridge: Cambridge University Press. doi:10.1017/CBO9780511814365

Coenen A.M.L. 1995. Neuronal activities underlying the electroencephalogram and evoked potentials of sleeping and waking: implications for information processing. Neurosci. Biobehav. R., 19: 447-463.


Conlee K.M., Stephens M.L., Rowan A.N., King L.A. 2005. Carbon dioxide for euthanasia: concerns regarding pain and distress, with special reference to mice and rats. Lab. Anim., 39: 137-161. doi:10.1258/0023677053739747

Council Regulation (EC). 2009. No 1099/2009 on the protection of animals at the time of killing. European Community Official Journal, L303:1-30

Dalmau A., Rodríguez P., Llonch P., Velarde A. 2010a. Stunning pigs with different gas mixtures. Part 2: aversion in pigs. Anim. Welfare, 19: 324-333

Dalmau A., Llonch P., Rodríguez P., Ruíz-de-la-Torre J.L., Manteca, X., Velarde A. 2010b. Stunning pigs with different gas mixtures. Part 1: gas stability. Anim. Welfare, 19: 315-323.

EFSA. 2004. Welfare aspects of animal stunning and killing method. Scientific report of the Scientific Panel of Animal Health and Welfare on a request from the Commission. Question. Adopted on the 15th of June 2004. Brussels. Available at: Accessed March 2016

EFSA. 2005. The Impact of the current housing and husbandry systems on the health and welfare of farmed domestic rabbits, 267, 1-31. Available at: Accessed March 2016

EFSA. 2013. Guidance on the assessment criteria for studies evaluating the effectiveness of stunning interventions regarding animal protection at the time of killing, EFSA J.,11: p. 41.

Forslid A. 1987. Transient neocortical, hippocampal and amygdaloid EEG silence induced by one minute inhalation of high concentration CO2 in swine. Acta Physiol. Scand., 130: 1-10. doi:10.1111/j.1748-1716.1987.tb08104.x

Forslid A. 1992. Muscle spasms during pre-slaughter carbon dioxide anaesthesia in swine. Fleischwirtschaft, 72: 167-168.

Leach M., Bowell V.A., Allan T.F., Morton D.B. 2002. Degrees of aversion shown by rats and mice to different concentrations of inhalational anaesthetics. Vet. Rec., 150: 808-815. doi:10.1136/vr.150.26.808

Llonch P., Andaluz A., Rodríguez P., Dalmau A., Jensen E.W., Manteca X., Velarde A. 2011. Assessment of consciousness during Propofol anaesthesia in pigs. Vet. Rec., 169: 496-497. doi:10.1136/vr.d5643

Llonch P., Rodríguez P., Velarde A., Abreu de Lima V., Dalmau A. 2012a. Aversion to the inhalation of nitrogen and carbon dioxide mixtures compared to high concentrations of carbon dioxide for stunning rabbits. Anim. Welfare, 21(S2): 123-129. doi:10.7120/096272812X13353700593923

Llonch P., Dalmau A., Rodríguez P., Manteca X., Velarde A. 2012b. Aversion to nitrogen and carbon dioxide mixtures for stunning pigs. Anim. Welfare, 21: 33-39. doi:10.7120/096272812799129475

Llonch P., Rodríguez P., Jospin M., Dalmau A., Manteca X., Velarde A. 2013. Assessment of unconsciousness in pigs during exposure to nitrogen and carbon dioxide mixtures. Animal, 7: 492-498. doi:10.1017/S1751731112001966

Llonch P., Rodríguez P., Casal N., Carreras R., Muñoz I., Dalmau A., Velarde A. 2015. Electrical stunning effectiveness with current levels than 1A in lambs and kid goats. Res. Vet. Sci., 98: 154-161. doi:10.1016/j.rvsc.2014.12.009

Nodari S.R., Lavazza A., Candotti P. 2009. Technical note: rabbit welfare during electrical stunning and slaughter at a commercial abattoir. World Rabbit Sci., 17: 163-167. doi:10.4995/wrs.2009.656

Raj A.B.M. 1999. Behaviour of pigs exposed to mixtures of gases and the time required to stun and kill them: welfare implications. Vet. Rec., 144: 165-168. doi:10.1136/vr.144.7.165

Raj A.B.M., Gregory N.G. 1995. Welfare implications of the gas stunning of pigs 1. Determination of aversion to the initial inhalation of carbon dioxide or argon. Anim. Welfare, 4: 273-280.

Raj A.B.M., Gregory N.G. 1996. Welfare implications of gas stunning of pigs 2. Stress of induction of anaesthesia. Anim. Welfare, 5: 71-78

Rodríguez P., Dalmau A., Ruiz-de-la-Torre J.L., Manteca X., Jensen E.W., Rodríguez B., Litvan H., Velarde A. 2008. Assessment of unconsciousness during carbon dioxide stunning in pigs. Anim. Welfare, 17: 341-349.

Smith W., Harrap S.B. 1997. Behavioural and cardiovascular responses of rats to euthanasia using carbon dioxide gas. Lab. Anim., 31: 337-46. doi:10.1258/002367797780596130

Velarde A., Cruz J., Gispert M., Carrión D., Ruiz-de-la-Torre J.L., Diestre A., Manteca X. 2007. Aversion to carbon dioxide stunning in pigs: effect of the carbon dioxide concentration and the halothane genotype. Anim. Welfare, 16: 513-522.

Velarde A., Gispert M., Faucitano L., Manteca X., Diestre A. 2000. Effect of stunning method on the incidence of PSE meat and haemorrhagies in pork carcasses. Meat Sci., 55: 309-314. doi:10.1016/S0309-1740(99)00158-8