Report on the use of Carbon dioxide stunning at Pork packers
Introduction
The abattoir at the Pork packer’s facility in Olifantsfontein is using a stunning method
whereby the pigs are exposed to a high concentration of carbon dioxide in order to render
the pigs unconscious before slaughter. While this system has some advantages over the
older method, the pigs have to endure severe aversion and respiratory distress for a
considerable amount of time before losing consciousness.
The manufacturing companyof the equipment needed to administer the gas, confirm in their
own PowerPoint presentation that carbon dioxide at a high concentration does not render
the pigs insensible and unconscious instantaneously. This company has only sold one unit in
South Africa, which is the one being used at Pork packers. While the company seems to be
expanding into South Africa it should be noted that they themselves are based in Denmark
and should be complying with council directive (93/119/EC). This legal requirement in their
own country states that all animals destined for meat consumption must be rendered
insensible instantaneously.
There is a worldwide consensus that using another inert gas called argon would be the
solution to the unnecessary suffering. Concerns regarding a faster return to consciousness in
pigs are not insurmountable, especially since the Meat Safety Act 40 of 2000 in South Africa
requires an animal to be bled within 60 seconds of stunning. Pork packers is not complying
with this at present. Inducing cardiac ventricular fibrillation post exposure to the argon
exposure is another option.
I do not believe that the cost implications should influence the type of gas used. The pork
industry in this country is transforming itself towards better welfare practices according to
the needs of the consumer. Two major supermarket chains have been working with the
major role players in the industry to improve the welfare of pigs from farrowing to slaughter.
1) Carbon dioxide stunning
Pork packers are using the automated dip lift system (Gondola system) to stun the
pigs. The pigs enter the chamber and are dropped into the pre-filled gas pit. A video,
obtained by the NSPCA on a court order in 2014, demonstrates that the pigs become
very excited, vocalise and in my opinion seem to be trying to escape when being
lowered into the pit where the CO2 is concentrated.
Reported times to unconsciousness or unresponsiveness have varied in the literature.
This has been attributed to different methods, types of pigs etc. The time to achieve
induction can therefore not be scientifically established as uniform. This abbatoir in
question is using an 81-83% CO2 concentration to stun. A study was done using a
similar dip lift system from the same company and it found the onset of
unconsciousness occurred after 37.6 seconds using a 90% CO2 concentration
(Llonchet al,2013, respectively).Studies have demonstrated that the higher the
concentration of CO2, the quicker the induction will be (Mota-Rojas et
al,2012).Insensibility can be determined by vocalization and squealing of pigs is
considered unacceptable (Grandin, 2013).On the video recording taken at this
facility, squealing can be heard at38 seconds after being lowered into the pit.
Carbon dioxide stunning is achieved by inducing hypercapnic hypoxia which results in
a decrease in the PH of the cerebrospinal fluid and the animal loses consciousness.
Loss of consciousness is not immediate and pigs experience aversion as the
concentration of C02 gas is increased (Velardeet al, 2007). Inhalation of CO2 at high
concentration causes irritation in the nasal mucous membranes and lungs, where the
presence of chemoreceptors acutely sensitive to this gas have been described
(Dalmauet al, 2010).Secondly it is a strong respiratory stimulator that provokes
hyperventilation and suffocation prior to the loss of consciousness (Rodriguez, 2008).
Unfortunately it is difficult to demonstrate it on a carcass as the acute nature of the
insult just before slaughterdoes not allow signs to be seen on post-mortem. It is
likely to be irritating to the eyes if it were to be extrapolated from the effects that
human beings have described in studies done (Gregory, 1990; Conlee, 2005).
There is also an issue with the uniformity of effects of the CO2 gas. The manager at
the facility has found differences in sexes but a study has confirmed that pigs
carrying the halothane gene are more likely to suffer from acute stress than those
that do not (Velardeet al, 2007).
2.) Argon induced anoxia/hypoxia
Inert gases such as argon induce unconsciousness differently to CO2 by causing
anoxia (total lack of oxygen) or hypoxia ( Low oxygen) in the blood which stops the
brain`s respiratory centre. In contrast to the carbon dioxide hypercapnia, research
has shown that hypoxia or anoxia does not cause aversion in pigs and does not
induce any signs of respiratory distress prior to the loss of consciousness (Dalmauet
al, 2010). The pigs would have to be exposed to Argon 90% in air (2% residual by
volume) for 5 minutes and then stuck within 45 seconds (Raj, 2008) which would
comply with the meat safety act in South Africa. There is also an option to induce
cardiac ventricular fibrillation using an electrical current after the pigs have been
exposed to anoxia for at least 90 seconds (Raj, 2008).
Argon can be mixed with carbon dioxide at a (60% / 30% ratio) or higher as it has
been shown to lessen the negative effects seen with high concentration C02
stunning but would still increase the time to unconsciousness and period of
consciousness compared to 90% CO2 (Raj, 1997; Raj and Gregory,1996).
Conclusion
The group handling system that is used at Pork packers has improved the welfare issue
associated with electrical stunning but clearly the current method is causing unnecessary
suffering to the pigs. Changing the system to one that improves the welfare aspect for the
thousands of pigs that are slaughtered there on a weekly basis should be a high priority to
the management.
References
1.) Rodriguez P, Dalmau A et al; Animal welfare 2008; 17:341-349
2.) Llonch P, Rodriguez P, Jospin M, Dalmau A; Animal 2013;7:3 pp 492-498
3.) Moja-Rojas D et al; International journal of pharmacology 2012;8(3):141-151
4.) Grandin T; Annual review of animal biosciences 2013;1:491-512
5.) Velarde A, Cruz J, Gispert M et al; Animal welfare 2007; 16:513-522
6.) Dalmau A, Rodriguez P et al; Animal welfare 2010; 19:325-333
7.) Gregory NG, Raj ABM et al; Animal welfare 1990; 70 (10):1173-4
8.) Conlee KM, Stephens ML, Rowan A and King LA; lab. Anim. 2005;39:137
9.) Raj ABM and Gregory NG; Animal welfare 1996;5:71-78
10.) Raj ABM et al; The veterinary journal 1997; 153:329-340
11.) Raj M. 2008. Welfare of pigs during stunning and slaughter. In: Faucitano L and
Schaefer AL (eds.), Welfare of Pigs from Birth to Slaughter (Wageningen, The
Netherlands: Wageningen Academic Publishers, pp.225-42).
Yours sincerely,
Dr. Bryce Marock, BVSc (Pret.)