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Roughly 9 billion chickens are slaughtered for food each year in the United States, and according to the poultry industry, each one of these sentient animals is mercifully stunned into unconsciousness before its neck is slit by an industrial blade. But scientists have come to a far more ghastly conclusion. Their research shows that the method favored by U.S. poultry processors to stun the birds ― moving them through a vat of electrified water ― does not consistently render birds insensible before slaughter. As a result, scientists say, an untold number of the chickens that we eat ― hundreds of millions of them and potentially many more ― likely experience intense suffering when they are slaughtered. Brain activity indicates that these animals may be capable of experiencing pain first when they receive a paralyzing electric shock that induces tonic muscle seizures, then when their throats are forced against a sharpened blade. The extent of suffering is almost certainly vast. If just 1 percent of chickens raised each year in the U.S. are not effectively stunned, it means roughly 90 million animals are experiencing a violent and painful death. That’s more than the total number of dogs kept as pets in this country. Unlike in Europe, there are virtually no U.S. regulations governing the humane slaughter of chickens. Nevertheless, following public pressure, the first major U.S. poultry producer, Perdue, pledged this year to phase out the use of electric water-baths. Now animal protection groups are pressuring Perdue’s competitors, like Tyson Foods, and large U.S. food service companies, like Aramark, to follow suit.

Immobilized chickens are shown exiting an electric water-bath stunner. (Credit: U.S. Poultry and Egg Association) Researchers say that a properly calibrated electric water-bath can reliably stun a large majority of birds that pass through it. But the devil is in the details. Each water-bath has various electricity settings (for features like current, voltage, and frequency), and changes to these settings involve major trade-offs. Using a lower-frequency charge increases the chance that a bird will be stunned, but it also raises the likelihood of damage to the bird’s carcass. Lower-frequency shocks can trigger more intense muscle seizures, sometimes causing fractured bones and ruptured blood vessels. The resulting meat can be too damaged or visually unappealing to sell. As a result, and with no animal welfare regulations to guide them, U.S. poultry companies use electric water-bath settings aimed at producing the best quality meat, not ensuring that chickens are reliably stunned. In other words, they use higher-frequency, lower-voltage shocks, which may leave birds paralyzed (so they can be easily whisked around the processing factory line) but not always unconscious, according to an extensive record of published studies that measured chickens’ brain activity after administering shocks at different settings.

Immobilized chickens have their throats cut by an industrial blade. Scientists believe many of them are conscious as it happens. (Credit: U.S. Poultry and Egg Association) No one knows how many individual chickens farmed in the U.S. might be conscious while they are slaughtered. Each processing plant uses its own water-bath settings, and none makes their settings public. Federal regulators don’t record the settings, let alone check that animals are unconscious before slaughter. Independent researchers say they are virtually never allowed to set foot in commercial processing plants. But scientists say what little is known about standard U.S. industry practices is cause for alarm. A review by Dr. Mohan Raj, the most widely cited researcher on this topic and an adviser to the European Union’s food safety agency, concluded, “We are aware of no direct evidence demonstrating that the electrical settings used in the United States are adequate to meet international standards for humane stunning and slaughter of poultry.” The co-author of that review, Dr. Sara Shields, who is now a welfare specialist for Humane Society International, told The Huffington Post that the settings used by U.S. poultry companies “have not been demonstrated to actually produce an effective stun.” Steve Wotton, a researcher at the University of Bristol’s School of Veterinary Sciences, one of the world’s leading centers for animal welfare research, said much the same. “The U.S. settings that have been reported to me and that I’ve read in published papers are far too low to stun.” A spokesman for Tyson Foods, the largest U.S. poultry processor, told HuffPost that “proper animal handling is an important moral and ethical obligation and we take it very seriously.” But, he acknowledged, “like most of the industry, our plants currently use low-voltage electrical stunning.” The company maintains no standard electrical settings, he added, “due to variation from plant to plant.”

Chickens experience a tonic seizure during the application of the electrical stun (in this footage, the stun is administered by an electrified head-only application rather than a water-bath). During a tonic seizure, “the body of the bird stiffens as muscles contract, the neck is arched, the legs are rigidly extended, rhythmic breathing stops, the eyes are wide open, and the blink reflex is absent.” Chickens at U.S. poultry facilities may be conscious during and following these seizures. (Credit: TopKip) Welfare researchers favor an alternative approach called “controlled atmosphere killing,” whereby birds are exposed to a steadily rising concentration of gas (typically carbon dioxide) until they irreversibly lose consciousness. More than 20 percent of chickens farmed in Europe are already stunned using controlled atmosphere killing systems, including the majority of chickens in Britain and about half in Sweden, a shift that has not led to price increases for consumers, analysts said. Even if electric stunners were perfectly effective, animal researchers say they would still be inferior because they involve several additional steps that can inflict pain on the billions of birds that are processed every year. To prepare for the water-bath, the birds must first be removed from their transport crates, an inelegant process that can result in broken bones and wings as chickens are dropped from their crates. Each bird is then turned upside-down and has its legs shackled into a metal conveyor. Nearly every aspect of this process causes the animals stress and pain, studies have found. Unlike humans, chickens do not have diaphragms, so when inverted their viscera compresses their heart and lungs. Chickens also have pain receptors in their legs, and studies show the shackling process causes bruising to thigh muscles and damage to their legs.

Chickens are inverted and shackled into a conveyor. (Credit: U.S. Poultry and Egg Association) Disoriented and in pain, about 90 percent of chickens flap their wings immediately after shackling. Because the birds that we eat are very young ― just six weeks old on average ― their joints and tendons are underdeveloped, so intense wing-flapping can lead to dislocated joints, broken bones and hemorrhages of the wing tip. Flapping can also cause birds to receive painful pre-stun shocks as their wings touch the electrified water before their heads are submerged. Footage of birds entering electric water-baths is rare, but one such video, posted online by a water-bath manufacturer, appears to show one or more ducks receiving pre-stun shocks as they approach an electrified bath. Warning: The footage may be unpleasant for some viewers.