The Disposal of Spent Laying Hens

Prepared by
Jacqueline Wepruk, B.A. Psych., M.E.Des.

Laying Hen Lifecycle
Humane Issues Surrounding Spent Hens and Their Disposal
Disposal Methods for Spent Laying Hens
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 hens.


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 plants.


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. (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..." (February 19, 1999).
6. Personal communication. Bernadette Cox, Canadian Egg Marketing Agency, March 15, 1999.


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 prevent osteoporosis.

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 processing plant.

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.

Market Variability

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 new products.7

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. 8

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), p. 1798-1802.
2. Ibid.
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), p. 13-29.
4. Ibid, p. 20-21.
5. Ibid, p. 20.
6. Overview of the Alberta Poultry Industry, Alberta Agriculture, Food and Rural Development, June 4, 1998.
7. Personal Communication, Jim Johnstone, poultry producer, March 5, 1999.
8. Newberry, p. 22.


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 device."1

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 include:

* 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 head

* shooting with a rifle,

* any new methods that aim at improving the humaneness of slaughter that the Minister approves for such purposes.3

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, ss.77-80, 1990.
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.
5. Ibid.


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) s. 148.


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 spent hens.

Each of these methods will be discussed in turn, with strengths and weaknesses outlined.

Water-Bath Stunning

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 being shackled.2

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. 6

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 are eliminated.

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 in Canada.


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. 13

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 hens.

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 5, 1999.
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 16, 1999.
11. Personal communication, Martin Zuidhof, March 5, 1999.
12. Newberry, et al, p. 25.
13. Personal communication, Keith Kalbfleish, March 12, 1999.
14. Personal communication, Dr. Mohan Raj, February 25, 1999.


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 is required.

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 implemented.

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