Animal rights groups have been quick to claim credit for Burger King Holdings Inc. recent announcement regarding changes to its animal product purchasing preferences. The company said it expects to increase its purchases of eggs from "cage-free hens" to 5 percent of its total egg purchases by the end of 2007. Burger King also expects to increase its pork volume purchased from "gestation crate-free" producers to 20 percent of its total pork volume by year end as well. But the policy change that could impact the USA broiler industry is the announced preference for chicken meat from processors who employ controlled atmosphere stunning (CAS) systems.

Both PETA and the Humane Society of the United States have claimed credit for the announced changes by Burger King, and both organizations trumpet these changes as a victory for the animal rights movement. "With its new policy changes, Burger King is signaling to agribusiness that the most inhumane factory farming practices are on the way out," said Wayne Pacelle, president and CEO of the Humane Society of the United States.

At the present time, only one broiler plant in the USA, MBA Poultry, Tecumseh, Neb., is using a CAS system as its exclusive means of stunning. Gold'n Plump Poultry, Inc., St. Cloud, Minn., installed and then later removed a CAS system at one of its broiler plants. According to industry sources, at least one major broiler processor was testing a CAS system at time of press, but CAS had not been adopted at any other plants as the exclusive means of stunning broilers.

CAS systems are employed by four USA turkey companies at plants that slaughter and debone heavy toms. Michigan Turkey Producers, Wyoming, Mich.; Dakota Provisions, Huron, S.D.; Jennie-O Turkey Store, Willmar, Minn.; and Cooper Farms, St. Henry, Ohio; all employ CAS systems. Other turkey processors are considering CAS systems, industry sources report.

Broiler CAS in the USA

Luciano Maradona, director of quality assurance, MBA Poultry, LLC, presented some of the pros and cons of the CAS system used by MBA at the U.S. Poultry & Egg Association Processor Workshop. MBA installed a Stork CAS system at its Tecumseh plant in 2005. Maradona said that using the CAS system has improved overall carcass and meat quality. Specifically, blood spots in breast meat, which had been found in 10 percent of breasts with electrical stunning, have virtually disappeared with CAS, according to Maradona. He said that the birds bleed-out better with the CAS than with electrical stunning and that the more complete bleed-out improves meat tenderness in addition to reducing the incidence of blood spots in breast meat.

Some research has shown that CAS can give early maturation of breast meat and reduce the amount of time required to age front halves. In Europe, some processors employing CAS deboned front halves immediately after air-chilling.

Maradona said that using the CAS system has reduced the number of broken wings and legs on the carcasses at the Tecumseh plant. He indicated that while staffing has not been reduced in live receiving and hanging with implementation of CAS, the work environment has been improved because there is less dust and noise.

MBA's CAS system uses a mixture of carbon dioxide and oxygen. The carbon dioxide cost for the Tecumseh plant is around $500 per week. Maradona said that there is an ethanol plant nearby, so MBA gets a good price on carbon dioxide, which is a by-product of ethanol production. The total gas cost for the system is around $0.003 per bird.

Maradona said that the CAS system requires more management time than electrical stunning does, because the CAS is a sophisticated piece of equipment. MBA has found that carbon dioxide levels for the CAS need to be tweaked with the changing seasons of the year; it gets quite cold in the winter in Nebraska and hot in the summer. It takes more carbon dioxide in the winter time to stun the birds since the birds come in to the plant with a slower metabolism due to the cold temperatures during transport.

Evaluating the options

Dr. A. Bruce Webster, poultry science professor, University of Georgia, has conducted a number of experiments where the behavior of chickens is monitored during CAS. Speaking about CAS at the Processor Workshop, he said that commercially available CAS systems were designed to minimize handling of the birds, because the birds are stunned prior to shackling, and to minimize carcass damage. Several different gas mixtures and methods of stunning or killing are being used, and there has been debate over the relative merits from an animal welfare standpoint of the various gas mixtures and techniques for administering the gas.


Some researchers and animal welfare advocates have questioned the merits of carbon dioxide use in CAS systems because birds are able to recognize the presence of carbon dioxide and show a natural aversion to the gas. Webster pointed out the carbon dioxide has several characteristics that are beneficial for use in CAS systems. Carbon dioxide produces anesthesia during the stunning process, and it can reduce convulsions associated with anoxia. Also, carbon dioxide is readily available and relatively inexpensive and, since it is heavier than air, it is relatively easy to contain.

A CAS working group which was comprised of European and American researchers on CAS and United Kingdom government representatives was convened in May 2005 to review existing research on CAS and come up with recommendations. The working group concluded that welfare related differences exist between CAS gas mixtures, but that these differences are not so great or unilateral as to give one gas mixture an advantage over the others.

Webster said that there are four types of CAS being done now (hypercapnic anoxia, anoxia, hypercapnic hyperoxygenation and hypercapnic hypoxia), and that all are acceptable means of stunning birds from an animal welfare standpoint. He also said that electrical stunning is not unacceptable. The welfare difference between electrical stunning and CAS is in the manner in which birds are unloaded from the cages and hung on the line. According to Webster, the welfare disadvantage of electrical stunning results from the removal from the cage and hanging of the bird before the bird is stunned. Webster said that it is better for the welfare of the birds if they are stunned prior to hanging them on the line or unloading them from the cages.

At the Poultry Handling and Care Conference in 2006, Webster showed videos of his CAS research. Birds stunned/ killed with CAS do "move around" or convulse in some manner. None of the gas mixtures produce a motionless death, so video of birds inside a CAS would not necessarily be any nicer to show the public than would video of birds in the blood tunnel using traditional electrical stunning and slaughter techniques.

CAS economics

Capital costs are higher for CAS than for electrical stunning and the gas cost is higher than the cost for electricity. CAS systems are relatively expensive when compared to electrical stunners. In many cases, switching to CAS in a turkey plant would require changes to live trailers and the live-receiving area of the plant. One commercially available CAS system, however, stuns turkeys while the birds are on the trailer. CAS systems have been developed for broilers which can stun birds while they are in standard industry cages.

CAS systems improve the work environment for the live hangers because there is less dust and noise and the ergonomics of the job are improved. It is easier to hang stunned broilers or turkeys than birds that are still moving. Traditional live-receiving systems for turkeys require that the live hangers remove the birds from the cage and then hang them on the shackle line. Most CAS systems for turkeys stun the birds in the cage and then automatically dump the birds from the cages. Live-hanging labor at some tom turkey plants employing CAS systems has been reduced by up to 50 percent. CAS would not provide the same level of labor savings for hanging turkey hens or broilers as it does for toms. In the case of MBA Poultry, a broiler plant, there was no reduction in staffing with CAS.

Overall, the economics of CAS for a given slaughter plant will depend on the type of birds being processed and a plant's finished product mix. CAS systems in use in the USA for broilers and turkeys have provided processors yield and grade improvements. The relative value of these improvements will depend on the type of birds being processed and the products produced. For example, a reduction in blood spots in breast meat is of more value to a deboning plant than to a cut-up or whole-bird plant. Industry sources report that yield improvements at turkey deboning plants employing CAS can easily offset the additional cost of using CAS.

Vacuum stunning: Another alternative?

Techno-Catch LLC has patented a vacuum stunning process and is conducting research with Dr. J. Paul Thaxton, Mississippi State University, Dr. Jodie Purswell and Dr. Scott Branton, both with USDA ARS. The prototype vacuum stunning system will stun an entire standard-size cage of broilers, and the company has begun testing the unit with a broiler integrator.

It takes about 30 seconds to pull the pressure down to about 20 percent of normal atmospheric pressure in the chamber, or 80 percent vacuum. Within 30 seconds at 80 percent vacuum the birds are dead. Vacuum stunning has a shorter cycle time than does CAS so less space would be required for a vacuum stunning system, and there is no gas cost. Vacuum stunning is still in the testing stage, and the system is not yet available for commercial use.