In the not too distant past, Europe routinely used gas stunning and the U.S. used electrical stunning during the harvest process at packing plants. However, this has all changed and the biggest driver of the change here has been pork quality. We stun hogs at the beginning of the harvest line because it is the law and for the welfare of the animals. Electrical stunning had always been the method of choice with the methods ranging from handheld wands to fully automated v-belt systems with electrodes in critical spots to convey the necessary amperage to the animal. We have perfected the electrical stunning system to include constant amperage rather than constant voltage and to include adjustments for resistance. We know all the factors in electrical stunning that can contribute to petechial hemorrhages or blood spots in the meat.
Only in the last 15 years has carbon dioxide stunning come into the U.S. as an option, and now over 250,000 head per day are stunned in this way compared to our daily harvest which is about 400,000. This includes eighteen large plants.
Why has there been such a large shift to gas stunning in the industry in such a short time? Increased interest in product quality accelerated about two decades ago, when development and pursuit of the export market intensified. There was also an interest in all the factors that can contribute to pork quality deterioration in the pig and in the carcass.
Certainly, there are several factors affecting pork quality during stunning. To slow the metabolic processes that continue to occur after exsanguinations (the removal of the blood), one must remove all the sources of heat in the carcass. These reservoirs of heat include the blood, the viscera, and finally the meat itself. Therefore, with electrical stunning, it is critical that the process move very quickly through blood removal, viscera removal and finally to the coolers for carcass chilling. With CO2 stunning, it is not nearly so critical to look at the stun-to-exsanguinations interval. In addition, broken backs, a problem associated with electrical stunning of heavy muscled hogs, is not a problem at all with gas stunning. The latter also allows for automated moving of groups to the stunner, which has great animal welfare and pork quality implications.
Even though CO2 stunning has become prevalent in the U.S., a couple of large companies have looked at the technology and decided to stick with electrical stunning. Their reasoning mostly relates to the detail approach they use in their plants. Electrical stunning can work with a minimum of blood splash; pale, soft, exudative (PSE) pork; and of broken backs if there is a focus on the system and an attention to detail. One company has implemented a computer-based system that uses low- and high-frequency stunning in combination. Company spokesmen say their outcomes are so good that they just cannot justify making the capitol investment necessary to bring a CO2 system on line.
Outside of Europe and in other parts of the world, not many areas that have moved away from electrical stunning at this point in time. However, as interest in pork quality increases and as more of these countries look for export opportunities, interest will probably increase. There is also a lot of interest in coming up with new, less expensive gas-stunning systems. It will be interesting to watch where this technology ends up.
Editor’s Note: Dr. Meisinger is the Executive Director of the U.S. Pork Center of Excellence. To contact Dr. Meisinger, e-mail him at: drdave@iastate.edu or call him by phone at: (515) 975-3557.
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