Warning: This story contains information that some readers may find distressing about the killing of animals for food products.
Bird flu means mass chicken killing. Some 200,000 hens in Otago were gassed in December to halt the spread of an avian influenza that had become highly pathogenic.
Shocking as the numbers sound, regularly killing many thousands of chickens is intrinsic to the egg and chicken-meat industries. The condemned birds had shortened lives due to the disease outbreak, but their death was routine. They were placed in crates and moved into containers into which almost pure CO₂ was piped. Mary van Andel, chief veterinary officer of the Ministry for Primary Industries (MPI), says a much lower CO₂ concentration mixed with less aversive gases is recommended but the very high concentration is allowed and used. Gassed chickens are required to fall unconscious within 35 seconds, and death should soon follow.
Chickens gasp, wing-flap and vocalise in response to elevated CO₂, suggesting they’re distressed. But it’s conceivable they’re not, says Professor Ngaio Beausoleil, who co-directs the Animal Welfare Science and Bioethics Centre at Massey University. “Birds show a lot of behaviours that could be conscious – or they could be just reflex behaviours. Because birds don’t show facial expressions, we don’t give them the benefit of the doubt like we do for mammals.”
She thinks we are obligated to understand what it’s like for them. “This is literally millions of animals in New Zealand that our law says are sentient and capable of having unpleasant experiences and suffering.”
For mammals, CO₂ killing is clearly inhumane, says Beausoleil. “Even at quite low levels of CO₂, about 7%, mammals show responses that align with what people show when they’re exposed to the same levels. Very unpleasant feelings of suffocation, breathlessness, anxiety and panic are consistent reports and behavioural responses. When you start to get higher than about 40%, we also see activation of pain receptors in the airways, the eyes and the nose lining.”
Some mammals overseas are killed with very high CO₂ levels. To settle whether birds suffer similarly, Beausoleil is part of an international research project funded by the UK government. It includes brain activation studies to look at whether areas involved in pain and fear light up in response to CO₂ and other gasses.
“We train animals to expect a certain treatment, like CO₂ exposure, in a particular location and then later we let them show us if they would go back there again if they have the choice, based on their memory of that treatment.”
In New Zealand, other sanctioned ways to kill adult chickens are neck dislocation and stunning in electrified water before neck cutting. All methods must meet the requirements of the Animal Welfare Act 1999, which says actions must not cause unreasonable or unnecessary pain or distress.
The words “unreasonable or unnecessary” do a lot of heavy lifting, though, as Rodriguez Ferrere, an associate professor of law at the University of Auckland, has pointed out. Society accepts that some pain and distress is reasonable and necessary to get affordable animal food products.
There are worse ways to die. Ventilation shutdown involves stopping a shed’s airflow so the heat from tens of thousands of chickens rises for hours until they die of heatstroke. One commentary by veterinarians stated “their pathophysiology suggests that animals are likely to experience pain, anxiety, nausea and heat distress,” and that such methods “often do not achieve 100% mortality”. Millions of chickens in the United States have died this way to control the feared H5N1 influenza, which many believe will eventually arrive here. MPI and the poultry industry say they will take all possible steps to ensure ventilation shutdown is not required.
