Everybody agrees that there is no good way to depopulate poultry in an emergency but there are times, such as during the outbreak of disease, when mass slaughter or “depopulation” of birds is the only way to protect human health.
So what is the “best” way to depopulate?
The jury’s still out.
Mass depopulation options that are currently available to respond to an
AI outbreak or natural disaster in the United States include cervical
dislocation, the use of carbon dioxide gas (CO2),
which includes whole or partial house gassing, containerized gassing
systems, gassing birds under polyethylene sheeting and other mobile
gassing or electrocution systems, and now firefighting foam.
No one method can cover all circumstances and each method has its pros
and cons. The challenge is to balance the protection of workers and
aggressive disease control with animal welfare issues while finding a
method that is practical, effective and humane.
While animal welfare advocates debate the physiology of the death of
the birds using foam, others continue to raise questions regarding the
practical application of firefighting foam.
The emergency use of firefighting foam was conditionally approved in
the United States in November 2006 for floor-housed poultry but it has
yet to be accepted as a viable option here in Canada.
An Emerging Technology
Bud Malone is an extension poultry specialist at the University of
Delaware. In 2004 he was faced with the challenges of
CO2 depopulation methods during an outbreak of low
pathogenic avian influenza. One of the responders on the disposal team
was also a volunteer firefighter who happened to mention using foam to
fight a fire at a poultry farm, and so the idea was conceived.
A team of University of Delaware researchers began to investigate the
use of firefighting foam as a mass depopulation method in hopes of
addressing challenges that arose during the use of carbon dioxide – challenges such as procuring adequate manpower, training and protecting
the team, disposal of contaminated material and the speed of response
to an emergency situation.
How Foam Works
Firefighting foam was originally used to fight fires as far back as the
late 1800s. The foam is designed to fight forest fires and certain
types of structural fires. The foam concentrate is technically known as
a synthetic detergent hydrocarbon surfactant and it is biodegradable
when mixed with water at the recommended ratios, typically around one
per cent concentration.
The mode of action in fire fighting is the formation of a foam blanket
with a consistency similar to shaving cream, cooling down the fire and
coating the fuel to prevent its contact with oxygen. With poultry, that
same foam blanket covers the flock with a blanket of foam whose bubble
size is small enough to enter the trachea and cause death by hypoxia.
Practical Considerations
At present there are two technologies available to apply the foam in the appropriate consistency and density.
The aerated nozzle-based system developed in North Carolina mixes water
and foam concentrates in collapsible tanks on the farm. This applicator
is more conducive to use in smaller houses where up to eight
individuals may be required to manoeuvre the hoses and nozzles in the
barn. In a disease control zone this technology would work best for
those houses not actively shedding the virus since it does require more
people coming in contact with the birds.
Kifco is an Illinois-based manufacturer and developer of commercial
irrigation equipment that has been working with researchers at the
University of Delaware to develop a high expansion foam generating
system for use in poultry barns called the Avi-FoamGuard. Andrew Baker,
spokesperson for Kifco, explained that the applicator looks like a
large-barrelled searchlight mounted on a three-wheeled trolley.
Baker described how the unit, which costs between $30,000 to $55,000
US, is retracted through the centre of the barn while a generator
delivers a medium-expansion foam with small, dense bubbles. The foam
rolls to the edges of the barn until an overall height is achieved to
cover up the tallest of the birds, which can be up to one metre or more
for large turkeys.
A broiler barn of 40 feet by 600 feet will take 72,000 cubic feet of
foam to fill to a height of three feet and will require 4,250 gallons
of water. The whole procedure for this size of barn would take about an
hour with two people needed to manage the equipment and only one of
those people needs to enter the house.
One of the major incentives to developing foam technology has been to
reduce the human health implications and the complications of working
with gas during zoonotic disease depopulation situations. Once a
responder has suited up with respirators, suits, boots and gloves to
the required level of personal protection and compliance for working
with gas, it’s not so easy to handle either the equipment or the birds.
The labour-intensive procedures that are involved with the four
acceptable methods for carbon dioxide depopulation (whole house,
container, polytent and mobile gassing systems) are avoided with foam.
In addition, the use of foam eliminates human exposure to carbon
dioxide or other gases that may pose safety risks to human health.
When the emergency involves a barn damaged by a tornado or earthquake
and perhaps unsafe to enter, foam may be the only practical option for
mass depopulation.
While firefighting foam is not readily available in large amounts in
Canada, it is commercially available and has a shelf life of up to 25
years, meaning that it can be stockpiled for emergency use as needed.
Carbon dioxide, on the other hand, can be difficult to secure in
adequate quantities in emergency situations.
Water is a potentially limiting factor to the use of foam, both in
terms of supply and quality or hardness. And as for disposal, foam is
compatible with composting of the dead birds.
Animal Welfare Issues
While some consider the use of foam to be humane, others refer to the
process as suffocation and as such find it unacceptable from an animal
welfare point of view. Proponents describe how a gentle wave of foam
quietly fills the house, while opponents claim that the foam just hides
the horrors of the dying birds.
Mass depopulation raises different issues than euthanasia and
unfortunately the issue of animal welfare does get complicated in
emergency situations. According to information on the American
Veterinary Medical Association (AVMA) website, “Mass depopulation
refers to methods by which large numbers of animals must be destroyed
quickly and efficiently with as much consideration given to the welfare
of the animals as practicable, but where the circumstances and tasks
facing those doing the depopulation are understood to be extenuating.
Euthanasia involves transitioning an animal to death in a manner that
is as painless and stress-free as possible. The AVMA currently
considers that destruction of poultry using water-based foam is a
method of mass depopulation and not a form of euthanasia. The AVMA
supports additional research to evaluate whether water-based foam can
be accepted as a form of euthanasia.”
Such research is ongoing as the technology develops.
Bud Malone explained that his research team has addressed the concern
that the foam may “drown” the birds. Through pathological examination
of dead birds they determined that no foam actually entered the lungs.
Death is caused by blockage in the trachea: the foam bubbles trigger
the rapid onset of hypoxia.
When carcasses were examined to compare death by foam, which physically
induces hypoxia, and carbon dioxide, which chemically induces hypoxia,
the lesions were consistent: the birds died by similar mechanisms.
Further research using blood analysis for corticosterone levels as an
indicator of stress has shown no difference in the birds’ stress
response between the depopulation methods.
Advocates of the use of carbon dioxide or other inert gases believe
that the gas renders the bird unconscious before death by hypoxia;
therefore, the addition of inert gas to the foam may help to avoid pain
or distress.
Malone’s original intent was to fill the foam bubbles with
CO2 gas. The research team studies, however,
showed that adding the gas did not reduce the time to death for the
birds. The use of foam alone is the safer method of mass depopulation
in terms of human health.
Mohan Raj is a senior research fellow in Food and Animal Science at the
University of Bristol in the U.K. His research is focused on effective
but humane slaughter of animals. Referring to euthanasia, he points to
a legal requirement of stunning methods to induce an immediate loss of
consciousness until death, and he maintains that any method of killing
should be without avoidable pain or distress.
To that end, Raj’s research continues to look into to addition of gas
to the foam. He points out that the foam needs to be robust enough to
feed through the house but the bubbles need to be fragile enough to
deliver the gas. In one trial he filled the foam with nitrogen, which
left the birds dead within 40 seconds, but the birds did experience
convulsions that need further trials to evaluate. Whether such wing
flapping is a sign of conscious suffering is not yet known.
Many questions remain unanswered, but if scientists can develop the
techniques and technology to include inert gases without increasing the
human health risk due to gas exposure it may further reduce some
welfare concerns.
Trial Runs
Foam was used for the first time in large-scale depopulation in West
Virginia in April and July of 2007 in response to the detection of low
pathogenic avian influenza in turkeys at two separate farms. Bud Malone
describes walking into a worst-case scenario: the large, market-ready
birds weighed in at 18 kilograms and required a depth of 1.2 to 1.5
metres of foam.
What did the response teams learn?
“These two foam depopulation events provided a great learning
experience and the opportunity to build on our knowledge base when
using this technology in the future,” said Malone.
He suggested three areas that need to be addressed after these events:
more training of qualified resource people is needed to operate and
maintain the mechanical systems and implement the proper procedures for
foam depopulation, and ample water supply of satisfactory quality and
an adequate supply of the proper type of foam concentrate need to be
sourced and delivered.
In July 2007, firefighting foam technology came to Canada. Ontario, to
be more precise. Dr. Harold Kloeze, co-chair of the Humane Destruction
Committee with the Canadian Food Inspection Agency (CFIA), was there.
As far as Kloeze was concerned, it failed. No one had counted on the
high limestone content of Ontario water that resulted in the foam not
foaming. He suggested that the foam method may be, “great under certain
conditions, but they may not exist here.”
Further research is needed to determine if a particular type of foam
concentrate may work better with hard water or if softening the water
is the answer.
Kloeze points to significant differences between the U.S. and Canadian
poultry industries that led to foam technology being, “probably not as
applicable here as there.”
For example, the infrastructure is not the same. In Delaware,
single-storey barns will house tens of millions of birds on earthen
floors where the use of plastic to seal the barns for
CO2 on such a large scale may be impractical. Here
in Ontario our barns are smaller and designed to keep out our Canadian
winters, which means they are also better constructed to keep in carbon
dioxide for use in the case of emergency depopulation. As well, many of
our barns are multi-storey buildings that are not designed to handle
the huge weight of the water involved in the foam depopulation method.
“Local solutions are needed,” says Kloeze. “Our industries aren’t the
same.” To that end, what he would like to see in the near future is an
inventory of housing types so that appropriate depopulation methods can
be evaluated and prescribed.
There are also practical dispensing problems with the foam which limit
its use at this time: while it pumps in well to open houses it doesn’t
flow around barriers such as cages, creating air pockets and reducing
the effectiveness of the process.
Conclusions?
For the Canadian poultry industry? There are no conclusions yet. The
debate continues. Kloeze says that the CFIA do not have a protocol at
this time for the use of firefighting foam and experts are awaiting the
results of further U.S. research.
In the U.S., “the recent conditional approval of water-based foam by
the USDA and endorsement by AVMA gives the poultry industry another
option for mass depopulation of flocks,” said Malone. “All methods used
for mass depopulation, particularly for zoonotic diseases, must take
into consideration, and balance, poultry welfare and human health; and
must minimize biosecurity risk and logistical challenges.”
At least firefighting foam offers another option for depopulation, and
while no option will ever be entirely palatable everyone seems to agree
that we’re just doing the best we can.
References:
American Veterinary Medical Association, Use of Water-Based Foam for the Depopulation of Poultry (2006).
http://www.avma.org/issues/policy/poultry_depopulation.asp
Malone, B., Benson, E., Alphin, B., Van Wicklen, G., and Pope, C., Methods of Mass Depopulation for Poultry Flocks with Highly
Infectious Disease (2007) Proceedings to Symposium on
Emerging Diseases, Queretaro, Mexico.
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