Scientific research has proven that using carbon dioxide to induce death is an effective and humane way to slaughter swine.
Until recently, however, the method was not an option because it was not USDA-approved.
But that changed on May 26 when the voluntary administration of carbon dioxide in slaughtering plants became legal. USDA, in its final ruling, said the use of carbon dioxide is consistent with the purpose of the Humane Slaughter Act, which is to render animals insensible to pain before slaughter. The rule appeared in the April 26 Federal Register. There are no plants currently using carbon dioxide to commercially slaughter swine
The change will not require swine to be asphyxiated by carbon dioxide before bleeding, but will permit exposure to concentrations of the gas for a sufficient amount of time for death to occur.
The swine should be in a state of surgical anesthesia throughout shackling, sticking and bleeding, except for swine in which death has been induced by the use of carbon dioxide, according to the rule.
The carbon dioxide gas is administered in a tunnel that is designed to permit effective exposure to the swine.
Two types of tunnels are commonly used for carbon dioxide anesthesia-U and Straight Line. Both are based on the principle that carbon dioxide gas has a higher specific gravity than air. The tunnels are opened at both ends for entry and exit of animals, and have a depressed central section.
Death-inducing carbon dioxide concentrations are maintained in the central sections of the tunnel, forming an effective anaesthetization.
Animals are driven from holding pens through pathways constructed of large-diameter pipe or smooth metal and onto continuous conveyor devices that move the swine through the tunnels. The animals are either compartmentalized on the conveyors by mechanical impellers or synchronized with the conveyor, which prevents crowding in the tunnel. While impellers are used to compartmentalize the animals, mechanically or manually operated gates are used to move the animals onto the conveyors. Swine that are killed are moved out of the tunnels on the same continuous conveyor.
Studies have shown that the necessary conditions for death to occur are a 95 percent to 98 percent carbon dioxide concentration and exposure time of between three and four minutes.
The death-to-bleeding interval should be no longer than two minutes to prevent pooling of blood intestines in edible organs, and no longer than five minutes to prevent the pooling of blood in muscle tissue.
USDA officials estimate that $50,000 to $100,000 per slaughtering line is needed to construct a carbon dioxide tunnel. The investment could be offset by a reduction of manpower for restraining, stunning and handling hogs after stunning.
Advocates of the process believe that it will lead to increased sales of pork products because hogs are more relaxed when stunned with carbon dioxide, which reduces the amount of undesirable meat. Also, less effort is expended on trimming and the removal of quality defects.
Under the rules for the use of carbon dioxide to anaesthetize animals before slaughter, plants are required to sample gas for analysis from representative locations within the gas tunnels. Gas concentrations and exposure times are to be recorded throughout each day's operations. The records are subject to FSIS standards and must be made available to inspectors.
The Danish and Swedish Meat Research Institute petitioned USDA to permit carbon dioxide to induce death based on studies demonstrating the beneficial effects on meat quality and the efficient handling of slaughtered swine.
Several Danish firms that export product to the United States are planning to install systems for stunning swine with carbon dioxide now that it is permitted. Prior to the regulation change, a company using carbon dioxide to induce death in swine could not export the product to the United States.
The use of carbon dioxide for stunning has been permitted in Europe since the early 20th century. During the past two decades, scientific research indicated that the stunning of slaughter animals with carbon dioxide is as effective as electrical stunning. Fewer injuries to animals and plant employees have also been
recorded.