The Disposal of Spent Laying
Jacqueline Wepruk, B.A. Psych., M.E.Des.
TABLE OF CONTENTS
Laying Hen Lifecycle
Humane Issues Surrounding Spent
Hens and Their Disposal
Disposal Methods for Spent
On-Farm Disposal Systems
Available Options - A Discussion
The issues surrounding the disposal of spent laying
hens are complex. This fact sheet is intended
as a source of information on potential resolutions
to the question of how to humanely dispose of
spent laying hens. Discussions within this publication
will include: a description of spent laying hens
in Canada, humane issues that surround spent laying
hen disposal, a discussion of current practices,
the case for improving disposal methods, available
humane options including their strengths and weaknesses,
and recommendations and conclusions. It is hoped
that open discussion of this topic within this
fact sheet, and the resulting dissemination of
information, will lead to future research and
advances in the humane disposal of spent laying
LAYING HEN LIFECYCLE
Hens generally being laying at 18 to 20 weeks
of age. Normally they are considered spent between
71 and 72 weeks of age. Therefore, laying hens
have a production lifespan of approximately one
year.1 In that year, hens lay an average of 288
eggs each.2 After peaking at 24 - 26 weeks of
age, a hen's production rate drops slowly. By
72 weeks of age a flock's egg production rate
can be down by 30%. Eventually, the hens will
cease to produce eggs and go into a moult. However,
laying hens in Canada are generally not allowed
to moult. If moulting does occur, hens will resume
laying eggs once new feathers are grown, but egg
production will be approximately 10 - 15% lower
than the first year.3
Numbers of spent laying hens are gradually decreasing
as egg consumption falls and as improved breeding
results in birds producing more eggs.4 In Canada,
approximately 22 million spent laying hens were
produced in 19955, and an estimated 18.5 million
for 1999.6 These numbers do not include hens from
very small unregistered producers, provincially
registered producers, or spent fowl arriving from
the United States for disposal at Canadian processing
1. Personal communication, Martin Zuidhof, Poultry
Specialist, Alberta Agriculture, March 5, 1999.
2. Overview of the Alberta Poultry Industry, Alberta
Agriculture, Food and Rural Development, June
4, 1998, p. iv.
3. University of Saskatchewan, Poultry Factsheets
#4 Egg Producing Chickens. http://eru.usask.ca/saf_corp/livestok/poultry/egg_chicken.htm
(December 8, 1998).
4. Personal communication, Dr. Ian Duncan, University
of Guelph, December 10,
5. Poultry Section, Animal Industry Division,
Market and Industry Services Branch, Agriculture
and Agri-Food Canada, "All about Canada's
egg industry..." http://www.agr.ca/misb/aisd/poultry/egg-fs.htm
(February 19, 1999).
6. Personal communication. Bernadette Cox, Canadian
Egg Marketing Agency, March 15, 1999.
SURROUNDING SPENT HENS AND THEIR DISPOSAL
The disposal of spent laying hens raises a number
of concerns regarding their humane treatment.
Spent laying hens tend to be physically fragile
by the end of their laying cycle. Removal from
cages can cause painful injuries due to the fragility
of their bones and the poor design of older cages.
Transportation to processing plants can expose
hens to inclement weather conditions over long
hauling distances. Market variability affects
the economic value of spent hens, sometimes challenging
producers to find more economically feasible means
of destroying spent flocks. These three issues
- fragile bones, transportation and market variability
- interact to create circumstances which can gravely
affect the humane disposal of spent laying hens.
Osteoporosis, or thinning of the bones, in laying
hens is a concern recognized by the researchers
and producers alike. Fragile bones in laying hens
can result in bone fractures during catching and
transportation. Osteoporosis in laying hens is
generally attributed to lack of exercise or weight
bearing, and the heavy demands for calcium during
eggshell formation. Lack of weight bearing is
known to weaken and reduce bone mass, thereby
increasing the incidence of broken bones during
handling. Calcium demands on laying hens can be
difficult to meet. Research into dietary means
of reducing osteoporosis have shown that while
a good diet can minimize bone fragility, it cannot
Research into the incidence of broken bones in
hens has reinforced welfare concerns. Between
24% and 29% of laying hens, on average, experience
broken bones by the time they reach the processing
plant, according to one study done in 1989.2 Bone
breakage in spent laying hens is a humane issue
because it is reasonable to assume that such injuries
cause pain to the animals involved. It is important
to note that catching methods can greatly reduce
the incidence of broken bones.3 Any method that
aims to improve upon the humane disposal of spent
hens must take into account the risks involved
with handling fragile birds.
Due to the generally low economic value placed
on spent laying hens, the number of processing
plants willing to accept them is limited. This
can mean that producers are forced to transport
their spent flocks over long distances to an available
processing plant. Transportation distances of
80 to 800 kilometers are common with economic
circumstances justifying trips upwards of 2,400
kilometers at times. This translates into transportation
times of 6 to 10 hours for hens travelling 500
to 800 kilometers. These transportation times
do not include loading and unloading time, which
can be from 2 to 4 hours at each point. One study
in Canada found that interprovincially transported
hens were in transit for 26 hours, while locally
transported birds took 18 hours to reach the processing
plant. "Dead on arrival" (DOA) and condemnation
rates (meat condemned by inspectors) can vary.
There is a general positive correlation between
numbers of DOA and condemned birds, and time spent
in transit, particularly in winter months.4 Excessive
heat or cold, previous injuries, vehicle vibration,
noise and light likely combine to stress spent
hens fur ther during their transportation to the
DOA figures of 2% to 4% and condemnation rates
between 5.4% and 9.2% serve to illustrate the
welfare concerns of transported spent hens.5 Agriculture
Canada has published the "Recommended code
of practice for the care and handling of poultry
from hatchery to processing plant," which
provides direction to producers, trans porters
and processing plants for the humane treatment
of poultry and recognizes welfare problems with
the handling and transportation of fowl.
The demand for spent hens can vary from year to
year depending upon a variety of conditions. Due
to the relatively limited amount of meat on spent
hens, they hold little monetary value as a food
product.6 In times of poor demand producers may
be hard pressed to find a processing plant willing
to take their spent flocks. The market can vary
so drastically that the disposal of one flock
can require the producer to pay, while the next
flock will reap some minor financial benefit.
Research and development is presently creating
a demand for spent hens in some areas, as their
carcasses are being used for the development of
Market variability also contributes to the transportation
concerns already discussed. As some processors
may be unwilling to take spent hens, producers
must transport their flocks further distances.
With limited access to processors willing to accept
spent hens during times of market falls, producers
may find their spent flocks to be a liability.
Producers require a means of humanely killing
spent flocks regardless of market conditions.
On-farm slaughter has arisen as a potential means
of protecting producers and their flocks from
variations in the market. On-farm slaughter may
be the preferred way of addressing other humane
issues regarding spent flock disposal. While bone
breakage may still occur wit h on-farm slaughter,
the duration of suffering would be lessened due
to the elimination of transportation. However,
any on-farm method should also provide a means
of salvaging the carcass for other uses.
1. T.G. Knowles and L.J. Wilkins, "The Problem
of Broken Bones During the Handling of Laying
Hens - A Review," Poultry Science, 77 (1998),
3. Ibid, p. 1798 and, Ruth C. Newberry, A. Bruce
Webster, Nora J. Lewis and Charles Van Arnam,
"Management of Spent Hens," Journal
of Applied Animal Welfare Science, 2(1) (1999),
4. Ibid, p. 20-21.
5. Ibid, p. 20.
6. Overview of the Alberta Poultry Industry, Alberta
Agriculture, Food and Rural Development, June
7. Personal Communication, Jim Johnstone, poultry
producer, March 5, 1999.
8. Newberry, p. 22.
FOR SPENT LAYING HENS
The federal "Meat Inspection Regulations,"
following from the Canada Meat Inspection Act,
outline acceptable methods for slaughtering and
rendering food animals unconscious prior to slaughter
at Registered Establishments. An example of a
Registered Establishment would be a federally
inspected processing plant. In such an establishment,
acceptable methods of rendering an animal unconscious
prior to slaughter include:
* exposure to carbon dioxide,
* application of an electric current causing immediate
loss of consciousness,
* "by delivering a blow to the head by means
of a penetrating or non-penetrating mechanical
Each of these methods is expected to result in
rapid unconsciousness ensuring that the animal
does not regain consciousness prior to its death.
Death must occur before an animal regains consciousness
and may be achieved through bleeding, electrocution
or, for birds and rabbits, decapitation.2
While the "Recommended code of practice for
the care and handling of poultry from hatchery
to processing plant" recommends adherence
to the above slaughter measures as outlined in
the "Meat Inspection Regulations", there
are no recommended provisions for on-farm slaughter
of poultry. Provincially inspected processing
plants must adhere to their respective provincial
legislation regarding humane slaughter. In Alberta,
for example, within the provincial "Meat
Inspection Regulations" acceptable methods
of rendering an animal unconscious prior to slaughter
* delivery of a penetrating or non-penetrating
blow using a mechanical device,
* exposure to carbon dioxide gas,
* by application of an electric current to the
* shooting with a rifle,
* any new methods that aim at improving the humaneness
of slaughter that the Minister approves for such
The disposal of spent laying hens raises issues
that do not neatly fit into the above list of
accepted means of slaughter As already noted,
on-farm slaughter is being promoted for spent
laying hens as an alternative to transportation
to processing plants.
Information on how egg producers are presently
disposing of their flocks is not collected nationally.
The Alberta Egg Producers Board is presently gathering
this information provincially, but details are
not available.4 This is an area where information
and recommendations are needed. At present some
animal welfare advocates have grave concerns over
what is happening to spent flocks.
A number of on-farm slaughter methods have been
receiving attention and hold promise for improving
the humane killing of spent flocks. A Modified
Atmosphere Killing cart has received some limited
use by egg producers. Processing plants have also
contributed to on-farm slaughter initiatives.
Oleet Processors in Saskatchewan have developed
a chicken macerator, while Northern Alberta Processors
have streamlined a mobile electrocution unit.
In the UK, Dr. Mohan Raj has developed a captive
bolt system that may have practical applications.
None of these on-farm slaughter methods has gained
widespread acceptance or popularity, as of yet.
Susan Gal of the Alberta Egg Producers Board has
stated that they are interested in promoting on-farm
slaughter and if a viable and humane method could
be recommended it would be included in their regulations.
5 These methods will be discussed in greater detail
later in this fact sheet.
1. Agriculture Canada, Meat Inspection Regulations,
2. Ibid, ss. 76-78.
3. Government of Alberta, "Meat inspection
Regulations," AR 51/73, January 10, 1999,
(May 12, 1999).
4. Personal communication, Susan Gal, Alberta
Egg Producers Board, March 5, 1999.
On farm killing systems have the potential to
greatly improve the humane disposal of spent hens.
The egg industry generally supports initiatives
by researchers to develop viable on-farm slaughter
methods. Promoters of on-farm slaughter, whatever
the specific method, believe that it better addresses
humane concerns surrounding spent hen disposal.
While bone breakage due to osteoporosis is still
a serious concern, on-farm slaughter does not
aggravate such injuries through transportation
to a processing plant. The additional stressors
of transportation, (vibration, cold, heat, water
deprivation, crowding and noise) are also avoided.
Market variability, which affects the demand for
spent hens, would play less of a role in on-farm
slaughter While there would be a cost associated
with on-farm slaughter, it would remain relatively
constant and allow egg producers to better predict
their total costs. Presently, transportation costs
can vary depending upon the fluctuating economic
value of spent hens. During times of high economic
value, hens slaughtered on-farm might still be
sent to processors for an added financial benefit.
A further justification for on-farm slaughter
lies in possible amendments to the Health of Animals
Regulations. The Expert Committee on Farm Animal
Welfare and Behaviour has given general support
to initiatives that would limit transport time
allowed for spent hens to 12 hours.1 This is in
contrast to the present regulations that allow
a maximum transport time of 36 hours for all monogastric
animals.2 The data already presented on transportation
times for spent fowl illustrate how restrictive
such legislation would be for egg producers who
do not have access to nearby processing plants.
If these amendments are implemented, then egg
producers would need to look to on-farm disposal
as an alternative.
One of the arguments against on-farm slaughter
is the difficulty of inspecting the process. Mobile
units travelling from farm to farm could not accommodate
provincial and federal inspectors effectively.
Most processing plants in Canada are inspected,
either federally or provincially to ensure food
safety. Certainly this issue would need to be
addressed in any method of on-farm slaughter where
the carcasses would be used for human consumption.
In addition, the on-farm or mobile units would
require some level of inspection to ensure good
working order, for the humaneness of the procedure
to be maintained.
1. Minutes of the 12th Annual Meeting of the Expert
Committee on Farm Animal Welfare and Behaviour,
June 12 - 13, 1998, Saskatoon, Saskatchewan, p.10.
2. Health of Animals Regulations, (C.R.C., c.296)
- A DISCUSSION
Five options in the disposal of spent laying hens
will be discussed. Water bath stunning is the
traditional method used at most processing plants.
Controlled atmosphere stunning involves gassing
birds with a combination of carbon dioxide and
argon gas. The macerator acts like a giant vacuum,
sucking birds up and killing them upon impact
with a high speed grinder. A modified mobile electrocution
method has been developed by Northern Alberta
Processors in conjunction with the Alberta SPCA
and Alberta Agriculture. In the UK, Dr. Mohan
Raj has developed a captive bolt system for killing
Each of these methods will be discussed in turn,
with strengths and weaknesses outlined.
Water-bath stunning tends to be the most common
method for rendering poultry unconscious prior
to manual or machine driven cutting of the neck.
Birds are taken from their holding crates and
shackled by the legs, while conscious, on a line
that leads to a water bath. The line is set up
so that the birds' heads will drop into the bath,
completing an electrical current which renders
the birds unconscious. 1
There are a number of humane concerns over the
use of this method, particularly for spent laying
hens. Transportation still exists as an issue
with water-bath stunning, as hens must travel
to a processing plant. It has also been established
that spent hens tend to have very fragile bones.
Shackling such birds, in a conscious state by
their legs, is likely to cause further pain and
broken bones, as well as fear. These new injuries
should be short-lived, however, as the birds pass
through the water bath less than one minute after
Studies have suggested that electrical stunning
is variable in its effectiveness. Birds can avoid
being stunned and even miss being cut. This could
mean that birds enter the scald tank alive and
conscious. Circumstantial evidence by a number
of researchers indicates that this is sometimes
the case at some plants. 3
The public is largely unaware of the water-bath
stunning method and of the humane issues it raises.
It is likely that the public would find the water-bath
stunner unacceptable if the concerns outlined
here were more widely known.
Controlled Atmosphere Stunning
The MAK (Modified Atmosphere Killing) cart is
one of the better known initiatives in controlled
atmosphere stunning in Canada. It is a portable
unit developed by Dr Bruce Webster at the University
of Georgia. Another controlled atmosphere stunning
device has been developed by researchers at the
University of Bristol, led by Dr. Mohan Raj. Controlled
atmosphere stunning has been used both within
processing plants and on-farm for euthanizing
poultry. The MAK cart displaces air with CO2 and
the Bristol device displaces air with a mixture
of argon and CO2 .
A modified version of the MAK unit was developed
under funding by the Alberta Egg Producers and
tested at the Poultry Research Centre of Alberta
Agriculture, Food and Rural Development and two
commercial-scale farms (4,000 and 14,000 birds).
The unit can be pushed down the aisles of a barn,
with 200 - 250 hens per load being placed inside
a CO2 enriched chamber Hens are unconscious within
15 - 20 seconds of being in the chamber. Results
from this study were very positive from a humane
and cost point of view.4 The unit itself costs
$2500 with the cost of CO2 per bird being 0.5¢.
An added benefit is that the removal of birds
can be done by regular workers and not special
catchers. One drawback, noted by Martin Zuidhof
of Alberta Agriculture, is the inability of the
unit to handle large volumes of birds at once.
The unit takes two people 5 minutes to load, with
90 seconds for each load of birds to be overcome.
For some producers this waiting time is too much,
as emptying a large barn can take 3 days as apposed
to 2 hours. 5
A commercial unit, developed by Mohan Raj, is
operated by Grampian Poultry in the UK. Large
frames holding 12 plastic drawers in four tiers
are loaded with 20 - 24 birds per drawer. The
frame, once full of birds, is taken by forklift
to a truck for transport to the processing plant.
Once at the plant the drawers are taken out of
the frame and placed on one end of a tunnel containing
a mixture of 30% CO2 and 60% argon gas. Each frame
takes about 2 minutes to move along a belt through
the tunnel. This process has been praised by a
number of individuals involved in the animal welfare
movement as a tremendous improvement in bird welfare.
In the UK experience, argon is an important component
of the gassing process. Straight CO2 is perceived
as causing distress when euthanizing animals,
as respiration becomes difficult.7 Anoxia, through
the use of argon gas, seems to alleviate respiratory
distress. Recommended mixtures of 60% argon and
30% CO2 have produced very satisfactory results
in terms of speed of unconsciousness, minimizing
distress and cost considerations. 8
Controlled atmosphere stunning is seen to have
a number of benefits over conventional methods
of euthanizing poultry. There is no shackling
of live birds, and hence less bone breakage and
stress. For the MAK unit there is even less concern
over bone breakage, as birds are euthanized immediately
after their removal from laying cages. With the
MAK unit used on-farm, humane concerns over transportation
The major concern with the MAK unit is its inability
to handle large volumes of birds over short time
periods. The larger controlled atmosphere stunning
devices, as developed in the UK, would require
a significant change in technology by processors
A macerator for use on-farm has been developed
by Oleet Processors in Regina, Saskatchewan. Their
unit "vacuums" birds down a 20 foot
long tube, to a grinder that kills the birds upon
impact with its blades.9 The system has been described
as very humane, with birds being killed quickly
upon entry into the vacuum tube.
While the system shows potential, some questions
remain to be answered regarding its humaneness.
Research is needed into the exact length of time
it takes for a hen to pass from the vacuum tube
to the grinder.10 It would appear that the macerator
holds potential as a humane option for on-site
euthanasia of spent laying hens, however, use
of the macerator is unsightly and the public's
aesthetic perception of this technology may be
difficult to overcome.
Northern Albert Processors have developed, in
conjunction with the Alberta SPCA and Alberta
Agriculture, an on-farm method for killing spent
hens. The mobile trailer unit has a high capacity
(4,000 - 4,500 birds per hour) and kills very
quickly. Birds are placed into a hopper, whereupon
they are dispatched by an electric current.11
Within 1 second birds are dropped onto a conveyor
belt leading to a rendering bin. The design of
the system is extremely important to ensure a
quick, human kill.12 Interestingly, the unit has
a MAK back-up system that can be used as an alternative.
Keith Kalbfleish, of Northern Alberta Processors,
explained that his company handles roughly 50%
of Alberta's spent laying hens with this method.
The company does not charge for farms requiring
the removal of 8,000 birds or more. For smaller
farms a $200 flat rate fee applies. The electrocution
device is more effective with cage raised birds,
as their lower density of feathers results in
better conductivity and a more efficient kill.
For free range systems 1/2 of 1% of birds are
not killed, due to their increased feather density,
and must be dispatched following electrocution.
Birds killed by this method do not need to be
removed from barns and taken to the mobile trailer.
Once again the potential for broken bones causing
distress is increased. However, the pain would
be more short-lived than with transportation to
processors. The Alberta SPCA and Alberta Agriculture
are satisfied with the results of the mobile electrocution
unit as a humane means of disposing of spent laying
Captive Bolt Gun
As a result of similar economic devaluing of spent
hens in the UK, Dr. Mohan Raj has engineered a
portable pneumatically operated captive bolt gun
using compressed air for on-site killing of hens.
The gun is a modification of a staple gun. What
follows, are Dr. Raj 's words in describing his
captive bolt gun.
"This has an expansion chamber at the rear
and, when the trigger is pulled, compressed air
propels the bolt to cause concussion of the brain
and also structurally damage it. This ensures
100% kill. The bolt should be 6 millimeters in
diameter, the compressed air pressure should be
a minimum of 8 bar or l20 psi. In our gun, using
these parameters, we are able to deliver the bolt
onto the skull at a velocity of about 50 meters
per second. We have evaluated [this method], using
evoked responses in the brain, and [are] fully
satisfied with it." 14
Dr. Raj emphasized that the gun must be held firmly
against the head of the bird, firing at a right
angle to the skull. in Dr. Raj's studies this
was achieved by holding the bird's head with one
hand and shooting with the other. This method
is time consuming and labour intensive, therefore
limiting its usefulness, particularly for larger
operations. A restraining device is presently
being developed which may address this issue.
1. Dr. Ian Duncan, "A report on the use of
gas in the United Kingdom to render poultry unconscious
prior to slaughter," Canadian Farm Animal
Care Trust, April 1997, p.2.
2. Ruth C. Newberry, A Bruce Webster, Nora J.
Lewis and Charles Van Arnam, "Management
of Spent Hens," Journal of Applied Animal
Welfare Science, 2(1) (1999), 22.
3. Duncan, p.2.
4. John Feddes and Martin Zuidhof, "Improving
the Wellbeing of Spent Layers," Poultry Research
Centre News, 6(1), (April 1997).
5. Personal communication, Martin Zuidhof, March
6. Duncan, p.10.
7. Duncan, p. 7-8.
8. J. P. Quine,
"Field Study of Controlled Atmosphere Stunning
in Poultry," Animal Welfare Foundation of
Canada, March 29, 1997, p.1.
9. Minutes of the 12th Annual Meeting of the Expert
Committee on Farm Animal Welfare and Behaviour,
June 12-13, 1998.
10. Personal communication, Dr. Ian Duncan, March
11. Personal communication, Martin Zuidhof, March
12. Newberry, et al, p. 25.
13. Personal communication, Keith Kalbfleish,
March 12, 1999.
14. Personal communication, Dr. Mohan Raj, February
The humane destruction of spent laying hens still
requires much development. Spent laying hens are
of special concern because of their increased
bone fragility, with on-farm slaughter promising
the most humane results. Some of the methods described
in this fact sheet may provide viable alternatives
but are not well known or tested. Further research
Market variability offers an incentive for egg
producers to find economical and humane methods
for euthanizing their flocks when market conditions
do not favor spent hens. On-farm disposal seems
to be the likely solution under these circum stances.
In developing more humane methods for euthanizing
spent hens, handling and transportation requirements
must be considered. An optimal method might be
one where no handling or transportation of live
birds is required, as both of these con cerns
can impact negatively upon hen welfare.
Public opinion is a little mentioned factor in
this debate, although an important one. The public
remains relatively ignorant of the issues surrounding
spent hen disposal. Egg producers should be concerned
about public reaction to these issues and continue
to play a proactive role in finding solutions.
Researchers and producers advocate improvements,
but change has been extremely slow. Industry-created
initiatives and solutions would illustrate to
the public the egg industry's commitment to solving
hen welfare issues.
As this fact sheet has shown, there are many potentially
viable options available, but the information
is not being widely disseminated. It is hoped
that through this fact sheet, information will
be shared, initiatives researched and solutions
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