Module 10 Euthanasia
- Compare and contrast the differences between capture methods and euthanasia techniques.
- Explain the reasons for using proper euthanasia techniques.
- Identify 4 signs that confirm death of an animal.
- Understand when a method meets AVMA guidelines.
- Explain 5 options for appropriate disposal of carcasses.
Terms to Know
Distress Includes pain or suffering; implies externally-caused, and usually temporary, physical or mental strain and stress.
Euthanasia good death (“eu” = good; “thanasia” = death), referring to techniques used to kill an animal as quickly and painlessly as possible.
Humane A practice or product that causes no unnecessary pain or stress for an animal.
Suffering A highly unpleasant emotional or physical response. Suffering implies conscious endurance of pain or distress
All NWCOs should deal with animals as humanely as possible, which means we should do everything in our power to reduce or eliminate pain, stress, and suffering when capturing, handling, and dispatching animals. As individuals, we should act with care and compassion for animals. As a society, we have determined through laws, regulations, and the judicial process that cruelty to animals is unacceptable and punishable. Using methods that are not approved or treating animals inhumanely can jeopardize a NWCO’s business and casts a shadow over the entire industry. Use good judgment, employ approved methods, and always strive to treat animals humanely.
In general, to be considered euthanasia, death must occur instantaneously or while the animal is unconscious. Euthanasia, as it pertains to wildlife control, includes use of lethal methods that are safe for the NWCO, the client, and the public, and are promptly carried out in a manner that causes the least amount of stress and suffering to the euthanized animal. The American Veterinary Medical Association (AVMA) decides whether a method meets euthanasia standards. Several methods meet the AVMA standard for euthanasia but this module covers only those suitable for NWCOs. Regardless of which AVMA-approved method for euthanasia is used, NWCOs are advised to reduce pain and stress to the animal as much as possible.
Capture Methods vs. Euthanasia vs. Humane Killing
It is important to distinguish between capture methods and euthanasia. For example, the use of a body-gripping trap to control a muskrat is a capture method, not a euthanasia technique. The trap will kill the muskrat quickly and humanely, but its primary function is to capture the target animal. In the same respect, shooting a free-ranging deer that is injured is now considered “humane killing” by the AVMA.
Euthanasia only refers to the deliberate death of an animal that is killed under the direct control of a person, either instantly or while the animal is unconscious.
The emotional involvement people have with wildlife leads us to recommend that the taking of any animal’s life, whether by a capture device, euthanasia method, or humane killing should occur out of public view. Failure to follow this advice may result in a great deal of unwanted attention and public scrutiny regarding your activities.
Disposition of Injured Wildlife
Wildlife that is captured, injured, and unfit to be released in accordance with state, county, or city regulations normally should be euthanized or humanely killed. Occasionally, depending on the species and the severity of injury, an animal may be turned over to a licensed wildlife rehabilitator for care and later release, provided the rehabilitator is aware of state requirements for translocation and agrees to comply. Develop a relationship with a local wildlife rehabilitator before those services are needed.
At the present time, many in the wildlife control industry consider euthanasia by carbon dioxide (CO2) induced narcosis to be the most user-friendly of the AVMA-suggested methods. Bottled CO2 gas is commonly used for euthanasia of animals in laboratory settings. The method requires a chamber in which CO2 replaces the available oxygen. The opportunity to euthanize an animal without injection, handling, or transfer is an advantage of using CO2. The use of CO2 to euthanize trapped animals under their control is not a pesticide use but is regulated as a drug under FDA.
Readily available at welding supply centers, CO2 is relatively inexpensive, safe, and easy to use, and when properly administered, will suppress the ability of an animal to experience pain prior to death.
A euthanasia chamber (Figure 1) is essential for euthanasia by CO2, and can be purchased from various providers. The chamber should be top-loading and large enough to hold your largest cage trap. Some NWCOs have small and large chambers for different sized traps.
Figure 1. A cage trap enclosed in a carbon-dioxide euthanasia chamber constructed with Plexiglas®.
Photo by Stephen M. Vantassel.
A chamber can be as simple as a plastic cooler, wooden box, or plastic trash can. Seal the bottom and sides with glue or caulk so that they are air tight. The lid, however, should NOT be air tight. Drill a hole in the side of the box 1 inch from the bottom for the CO2 delivery tube. Carbon dioxide is heavier than air. As the gas enters the chamber, the CO2 displaces the air out of the top of the box, which is why the lid should not be air tight.
A welding supply company or bottled gas supplier will be able to provide you with a CO2 tank, gas regulator, flow meters, and tubes. Only use bottled CO2 gas. Ask the supplier about all relevant laws and regulations concerning the handling, storage, and transportation of pressurized tanks. Improper handling of tanks can result in serious injuries and property damage.
Your goal is to minimize the pain and stress of animals whenever possible. The following are suggestions for stress reduction:
- Place one animal in a chamber at a time.
- Animals should not see other individuals being euthanized.
- Handle animals as gently and as little as possible before and during the euthanasia process. Animals can be kept calm by covering traps with old blankets or tarps. Speak in calm tones.
Fill the chamber with CO2 at a rate of 20% per minute after a caged animal is placed in the chamber. The flow rate can be calculated for your particular chamber by following this procedure.
- Measure the internal length, width, and height of the chamber in inches.
- Multiply the three measurements (length x height x width) to determine the chamber’s volume in cubic inches (e.g., 13- x 13- x 33-inch tank = 5,577 cubic inches).
- Divide the volume by 61 to convert the units to liters (5,577 divided by 61 = 91.4 liters).
- Multiply the new volume by 0.2 to obtain a fill rate of 20% per minute (91.4 x 0.2 = 18.3 liters).
- Set the gravity-flow meter to the calculated fill rate (18.3 liters per minute in this case) and leave it on to fill the tank completely in 5 minutes.
After the chamber has filled, reduce the rate of flow to 3 to 5 liters per minute to save gas. Do not turn the flow off so that the pressure remains positive and prevents fresh air from reentering the chamber. Some animals, such as squirrels and adult raccoons, expire quickly. Skunks, infant raccoons, and woodchucks may take 30 minutes or more to expire. In all circumstances, it is imperative that you confirm the death of the animal. Animals succumbing to CO2 frequently will start shaking their heads, then exhibit shivering along with rapid and deep breathing, followed by lying down with shallow to barely perceptible breathing.
The following statement is from the AVMA Guidelines for the Euthanasia of Animals (2013), “Cervical dislocation is a technique that has been used for many years and, when performed by well-trained individuals, appears to be humane.” Manual cervical dislocation is a humane technique for euthanasia of poultry, other small birds, mice, rats weighing less than 7 ounces, and rabbits weighing less than 2¼ pounds, when performed by individuals with a demonstrated high degree of technical proficiency.
To euthanize mice and rats with cervical dislocation, place your thumb and index finger on either side of the neck at the base of the skull or press a rod at the base of the skull. With the other hand, quickly pull the base of the tail or the hind limbs to separate the cervical vertebrae from the skull. To euthanize immature rabbits, hold the head in one hand and the hind limbs in the other. Stretch the animal to hyper-extend the neck and twist dorsally to separate the first cervical vertebrae from the skull. Cervical dislocation by stretching is a common method for euthanizing poultry, but loss of consciousness may not be instantaneous. Data suggest that electrical activity in the brain persists for 13 seconds following cervical dislocation.
Advantages of cervical dislocation may include: (1) rapid loss of consciousness, (2) no chemical contamination of tissue, and (3) it can be rapidly accomplished.
Disadvantages of cervical dislocation include that: (1) it can be aesthetically unpleasant, (2) it requires a mastery of technical skills to ensure loss of consciousness is rapidly induced, and (3) it is limited to poultry, other small birds, mice, and immature rats and rabbits.
In lieu of demonstrated technical competency, animals must be sedated or anesthetized prior to cervical dislocation. The large muscle mass in the cervical area of heavy rats and rabbits makes manual cervical dislocation physically more difficult. Those responsible for the use of this technique must ensure that personnel performing cervical dislocation techniques have been properly trained and consistently apply it humanely and effectively.
When shooting is used as a means of euthanasia, personnel should be trained in the safe use of firearms and anatomy of the species involved.
Shooting can be done only where it is legal to discharge firearms. Check local ordinances before using this technique. The firearm and ammunition should be appropriate for the size of the animal. If the animal is not going to be tested for rabies, place the shot at a point midway between the eyes and base of the ears (Figure 2), but slightly off-centered to avoid the bony ridge that runs down the middle of the skull.
If the animal is to be tested for rabies, do not shoot it in the head. A test for rabies requires brain tissue. Restrain the animal with a catch pole and shoot it in the heart and lung area using a low caliber rifle or pistol, or consider using another method of euthanasia, such as CO2.
An optimal shot will pass through the cranium at a slightly downward angle towards the spinal cord. Although a correct shot will instantly render the animal unconscious, thrashing, muscle spasms, and bleeding may continue afterwards for a brief time.
You can stun a small- to medium-sized animal by hitting the back of its head quickly and firmly with a blunt instrument, such as a baton or hammer, or a non-penetrating captive bolt. When properly administered, a blow to the head causes immediate unconsciousness due to destruction of brain tissue, followed quickly by death. Properly trained personnel can use stunning to rapidly and humanely dispatch wild animals restrained by foothold traps or snares. Stunning sometimes only renders an animal unconscious. Therefore it may need to be followed immediately by a second dispatch method such as cervical dislocation or shooting to ensure death.
Some animals may display involuntary muscle movements after stunning, therefore this may not be the appropriate method of dispatch to use within viewing distance of the public.
Figure 2. Diagrams illustrating bullet placement for euthanasia by shooting. Raccoon image by Gary Lunsford, bovine images by UNL.
Injectable drugs, such as anesthetics or barbiturates, sometimes are used to euthanize wild animals. However, the Drug Enforcement Agency (DEA) regulates these “scheduled drugs” and only individuals registered with the DEA can legally possess them. Consequently, this method is seldom available to anyone other than a certified veterinarian. If you have access to a licensed veterinarian or an animal shelter, they may be able to dispatch wildlife for you using injectable drugs.
Carcasses of animals that have been euthanized with scheduled drugs must be buried at least 3 feet or incinerated to avoid exposure to scavengers.
A variety of dispatch methods are considered unacceptable or inhumane for use in wildlife, even though they are sometimes used by certain individuals. Often these techniques are selected because of convenience. Challenges presented by field conditions should not lessen the ethical obligation of the NWCO to reduce pain and distress to the greatest extent possible.
Unacceptable methods of dispatch in wildlife include: drowning, carbon monoxide overdose, a stunning blow to the top of the head, gunshot to the abdomen, administering paralysis-inducing drugs, freezing, burning, and injection of solvents or household products.
Confirmation of Death
To make absolutely sure a small animal is dead, you may perform cervical dislocation or decapitation. Decapitation quickly separates the head of an animal from its body. This method is most often used to humanely dispatch rodents, birds, and small rabbits (Andrews et al. 1993). The guillotine is the preferred decapitation tool. It works instantly and reliably.
This method should only be used on wild animals that are sedated or unconscious. Wild animals that are awake will experience distress when restrained.
Most people find decapitation disturbing. Violent muscle contractions may occur after the procedure, therefore this method may not be appropriate if members of the general public are within viewing distance.
Confirmation of death can be difficult in a field setting. We recommend that you consider all the following signs to determine whether the animal truly is dead.
Thoracic compression (the application of pressure to the chest to restrict respiration) previously was considered acceptable for euthanasia of small mammals. However, based on the 2013 AVMA Guidelines, this is now considered unacceptable unless the animal is deeply sedated or insentient for other reasons. Protect yourself from exposure to teeth and body fluids while performing these additional techniques. Rigor mortis (animal is stiff), putrification, or loss of vital organs also are conclusive proof of death. Some states require that NWCOs record the disposition of wildlife. Always keep accurate records.
Confirmation of Death
- Respiration has stopped – check if the chest has stopped expanding and contracting for at least 3 minutes. You may have to look carefully, as some animals have very shallow breathing.
- Corneal reflex has ceased – the animal should no longer blink (even when touched), the eyes should be fixed, and the pupils (the black portion of the eye) dilated.
- Muscle tone is limp – dead animals will not be able to stand and should appear limp and flaccid.
- Heart has stopped beating – a stethoscope and training is needed to identify this sign properly.
Disposal of Carcasses
Disposal of carcasses must be done safely, in a manner respectful of public sensitivities, and in accordance with state and local guidelines. Check with your local authorities before dealing with animals so that you are aware of all recommended options for disposing of carcasses.
Proper disposal methods include:
- above ground (dispersal and composting),
- below ground (individual and common graves),
- landfill, and
Above ground disposal, burial, or disposal via a licensed dead animal dealer are preferred and encouraged over disposal via incineration or in a landfill. Always wear thick leather gloves to reduce the risk of being scratched or exposed to animal fluids when handling a carcass. Welder’s gloves are durable and provide protection to the hands and wrists. For additional protection, wear latex or vinyl gloves inside the leather gloves. Ticks and fleas present a health risk as they leave the carcass in search of a new host.
Above-ground disposal is easy because no digging is involved. It is gaining in popularity as an environmentally responsible way to recycle wildlife into the ecosystem. It requires landowner permission and is not recommended for carcasses of sick (or suspected of being sick) or poisoned animals. Choose isolated locations to reduce encounters with pets and people, and do not overuse a location. Two forms of above-ground disposal are available.
Above-ground Dispersal – involves the distributing of carcasses above ground so that the natural processes of decay, decomposition, and scavenging can take place. Dispersal increases the likelihood of attracting scavengers that feed on carcasses. Transmission of diseases is a concern, as well as odor control and unsightliness. Sites should be at least 100 yards from surface water and areas of human habitation. Check state and local regulations.
Composting – is an inexpensive alternative that when done properly, kills most pathogens and provides a composted material for amending soil and growing crops. All of the following conditions must be met for composting carcasses:
- the site must be more than 200 feet from any body of water, waterway, well, or spring;
- lay a 24-inch bed of wood chips or other organic bulk on the ground;
- lay the carcass in the middle of the bed and cover it with another 24-inches of dry sawdust or other organic bulk;
- additional carcasses can be layered into the pile, again with 24-inch layers of organic bulk;
- fence the area with woven wire to exclude potential scavengers; and
- let the pile set for 4 to 6 months. The pile can be turned after 3 months to speed the composting process.
Below-ground disposal conceals the sights and smells of decomposition from people and scavengers. The digging of graves, however, can be quite laborious when used for several carcasses. Two forms of below-ground disposal are available.
Individual Graves – are used to dispose of one animal at a time. They require a single hole for each carcass, often dug by hand with a shovel or post-hole digger. All of the following conditions must be met for an individual grave (Figure 3):
- the grave must be located at least 200 feet from any groundwater well that is used to supply potable drinking water,
- the carcass must be covered by at least 2 feet of soil within 24 hours after burial,
- the carcass must not come into contact with surface or groundwater, and
- the number of individual graves must not exceed 100 graves per acre.
Figure 3. Woodchuck placed in an individual grave. Photo by Stephen M. Vantassel.
Common Graves – are used to dispose of several carcasses at a time. They typically require a much larger hole than individual graves, which may require the use of a backhoe or excavator. All of the following conditions must be met for common graves:
- pits must be located at least 200 feet from any groundwater well that is used to supply potable drinking water,
- carcasses must not come into contact with surface or groundwater and must not be disposed of in a 100-year floodplain or wetland area as defined by the Solid Waste Management Act,
- the number of carcasses should not exceed 250,
- carcasses must be covered with at least 12 inches of soil within 24 hours after burial,
- pits should not remain open for more than 30 days,
- common graves should have at least 4 feet of soil as final cover, and
- the number of common graves should not exceed 5 graves per acre.
An incinerator must be approved by state and local authorities to burn animal carcasses. Incineration can cost more than $0.50 per pound, making it relatively expensive.
Carcasses taken to a licensed landfill must be securely enclosed in a plastic bag or other suitable airtight container to prevent noxious odors. They may be disposed of at a Type-II, licensed, solid-waste disposal facility (standard landfill) or at an out-of-state facility in accordance with that state’s solid waste disposal regulations.
Carcasses may be disposed of by companies that provide rendering services, which is the process of using heat and separation to convert waste animal tissue into stable materials such as lard, dried animal protein, and bone meal. Most rendering services require large-bodied animals, such as horses or cattle. Availability of rendering services is limited in many areas.
Reviewed by Gary Lunsford, Tulsa Zoo
AVMA Guidelines for the Euthanasia of Animals 2013 Edition. https://www.avma.org/KB/Policies/Documents/euthanasia.pdf
Julien, T.J., S.M. Vantassel, S.R. Groepper, and S.E. Hygnstrom. 2010 Euthanasia methods in field settings for wildlife damage management. Human-Wildlife Interactions 4:158-164. http://www.berrymaninstitute.org/files/uploads/pdf/journal/fall2010/HWI_4_2Fall_2010_Full.pdf#page=12