Avian Wildlife Euthanasia Techniques

Ruddy Duck

Stay tuned

Stay tuned for a webinar recording coming this winter, RACE-approved for 1 hour of continuing education credit.

Presenter: Renée Schott, DVM, CWR

Lecture objectives

Sick wild finch
  • Define euthanasia and discuss where suffering happens (brain)
  • Provide a framework under which to evaluate euthanasia methods
  • Provide a practical process flow
Use the following cases to illustrate various euthanasia methods and evaluate using framework

  • Songbird:
    • Inhalant: discuss avian respiratory physiology
      • Isoflurane
      • Carbon dioxide (CO2)
    • Sodium pentobarbital and the various routes of administration
    • Physical
      • Blunt force trauma
      • Cervical dislocation
      • Decapitation
      • Captive/penetrating bolt
  • Goose
    • Inhalant: discuss breath-holding
    • Other pre medications followed by sodium pentobarbital, various routes
    • Physical

Abstract

Wildlife often present to veterinarians and wildlife rehabilitators with conditions that warrant euthanasia. It can be difficult, however, to apply mammalian methods of euthanasia to species with unique physiology such as birds. This seminar will begin with a discussion on suffering and the definition of euthanasia. A framework will be provided under which to evaluate euthanasia methods as well as a practical process flow. This interactive presentation will use cases to discuss practical euthanasia methods for birds and the physiology pertinent to these methods compared to others.

Please Note: The decision to euthanize will NOT be covered in this course. Visit Basic Wildlife Rehabilitation Triage by Dr. Renée Schott for some guidance on this matter.

Also visit, the RACE-approved webinar recording, Reptile Wildlife Euthanasia Techniques.

 

Recommended reading

Before viewing this webinar recording, Dr. Schott strongly recommends attendees read the brief article “Euthanasia: Quality of the Life” by Katherine McKeever. This copyrighted material is reprinted with permission of the National Wildlife Rehabilitators Association from Principles of Wildlife Rehabilitation, 2nd edition, 2002 (pp 215-216).

 

Webinar recording

Stay Tuned: Recording coming in fall 2020.

 

Outline

Download a PDF version of Dr. Schott’s outline and references.

Please note:  These notes are intended to serve as a supplement or aid during the webinar recording, and will likely be updated before the webinar recording is posted.

 

  1. Wildlife rehabilitation is the act of providing temporary care to injured, sick, or orphaned wildlife with the goal of releasing them back into the wild.1
  2. Legality
    1. If the animal is wild, its “owner” is the State, Federal, or Tribal authority
    2. Some endangered or migratory species may require approval by the appropriate federal agency prior to euthanasia.2
      1. Migratory birds = USFW
      2. Marine mammals = NOAA
      3. Remainder usually = State
  3. Definition
    1. Euthanasia is derived from the Greek terms 3
      “eu” = well or good
      “thanatos” = death
    2. Ending the life of an animal in a way that eliminates or minimizes pain and distress.4
    3. The technique employed should result in rapid loss of consciousness followed by cardiac or respiratory arrest and, ultimately, a loss of brain function.
    4. Actually determining the pain or distress of a method of euthanasia can be very difficult because as humans we will never fully know/understand the subjective experience of the animal3.
      1. We use our best judgement; paddling, vocalizations, convulsions before apparent loss of consciousness is obviously suffering.
      2. We also use our knowledge of physiology and assume suffering in the absence of behaviors if a physiological process theoretically leads to suffering.
    5. General rule: A gentle death that takes longer is preferable to a rapid but more distressing death and conversely, if all other methods are equally humane, the quickest method should be chosen.5
    6. Taking a life is abhorrent to many (McMillan)6 we often forget this and need to keep it in mind
    7. What’s the difference between euthanasia and humane killing? 4,6,7
      1. Most veterinary/animal fields define euthanasia simply as “good death”, however, the human field does not.
        1. Humane slaughter
        2. Humane depopulation
      2. The decision of whether or not to end a life must be based on the animal’s welfare, that is, to anticipate what is in the animal’s best interest.
  4. Evaluating euthanasia methods 4
    1. Animal factors
      1. Ability to induce loss of consciousness and death with a minimum of pain and distress; compatibility with species, age, and health status
      2. Time required to induce loss of consciousness (CCAC)3
      3. Reliability/irreversibility
    2. Human factors
      1. Safety of personnel
      2. Documented emotional effect on observers or operators
        • Emotional impact
        • Drug availability and human abuse potential
      3. Ability to maintain equipment in proper working order
      4. Legal requirements
    3. Remains (carcass) factors
      1. Compatibility with intended animal use and purpose
      2. Compatibility with subsequent evaluation, examination, or use of tissue
      3. Environmental impacts
    4. Unacceptable methods
  5. We must view the above within a practical systems view/process flow:
    1. Handling/restraint
    2. Euthanasia methods/agents: two phases 8
      • Loss of consciousness (unaware of surroundings, cannot feel pain, fear, distress)
        • Sedation= animal may be aroused to a conscious state with sufficient stimulation 4
        • Anesthesia= unconsciousness and cannot be aroused 4
      • Causing death
    3. Confirmation of death
    4. Disposal of remains, necropsy needed (and why)
  6. Techniques
    1. Inhalant agents
      1. Gas displacement rate is critical for the humane application of inhalant euthanasia when using a flowmeter 4
      2. Isoflurane 4
      3. Carbon dioxide
        1. Rodents: recommendations changed = 30-70% of the chamber/cage volume/min (fill it faster?)
        2. May cause distress in animals by three mechanisms 4: (CO2→respiratory acidosis)
        1. Pain due to formation of carbonic acid on respiratory and ocular membranes (pain starts at about 40% CO2 in people and apparently rats/cats
        2. Feeling of breathlessness→ in humans, this starts at 8% and intensifies with higher concentrations
        3. Direct stimulation of ion channels with the amygdala associated with the fear response
      4. Sodium pentobarbital
        1. How sodium pentobarbital works in mammals 9
        2. Routes of administration
        3. Sodium pentobarbital solutions are caustic and it can hurt if given in an inappropriate spot
      5. Physical methods:
        1. “When properly used by skilled personnel with well-maintained equipment, physical methods of euthanasia may result in less fear and anxiety and be more rapid, painless, humane and practical than other forms of euthanasia.” 4
    2. Case examples
      1. SONGBIRD: @ vet clinic describe case, medical issues, state why we are euthanizing (i.e. spinal trauma with no deep pain)
      2. Ask what euthanasia method would others use for this? Carbon dioxide and isoflurane (with or without sodium pentobarbital injection) will be suggested.
      3. Avian respiratory physiology:
        1. Much for efficient at gas exchange vs mammals because of:
          1. Unidirectional air flow through lungs (no mixing of inspired and expired air)
          2. Countercurrent gas exchange (which is much more efficient and increases surface area over which gas can be exchanged and more/smaller air capillaries
          3. → more sensitive to inspired toxicants
        2. Inhalant agents:
          1. Gas displacement rate is key: critical to the humane application of inhalant euthanasia when using a flowmeter 4
            1. Time constant (τ) = volume/flow rate
            2. 1 τ required for concentration of inflowing gas to reach 63.2%
            3. 2 τ required for concentration of inflowing gas to reach 86.5%
            4. 3 τ required for concentration of inflowing gas to reach 95%
          2. Isoflurane2:
            1. Smells noxious, irritates respiratory epithelium → animals may breath hold → may cause distress
            2. Expose only to vapors, not the liquid (irritating to skin)
            3. Maximum 33% isoflurane vapor can be produced at 20°C
            4. Feeding euthanized animals to patients? whole body still retained between 4% and 13% of the absorbed dose. Differences between sevoflurane and desflurane were obvious only during the final stages of elimination; large amounts of anesthetics are absorbed during anesthesia and significant amounts remain in the body for days after apparent recovery.10
          3. Best for small animals, less than 7 kg
          4. Best when no aversion behaviors are noted → exposure to rapid high concentrations preferred in some species
          5. Expose the animal to a high gas concentration using an anesthetic vaporizer or soaked gauze in a closed container 11; gauze or cotton soaked in container 12
            1. Vapors are inhaled until respiration ceases and death ensues 11
            2. Vapor exposure should be maintained for at least 3 minutes after apparent clinical death 11

Sodium pentobarbital

  1. Sodium salts (phenobarbital, phenytoin, methotrexate) are considered weak acids and must be formulated at a high pH to ensure solubility.13 Phenytoin sodium = pH 12
  2. Sodium pentobarbital alone; ~390 mg/ml, dose ~1 ml/4.5 kg (10 lbs)
    1. Fatal-Plus: DEA schedule II
      1. Thin (not viscous)
      2. pH=9.6-11 (caustic! Hurts if given near nerves!)
    2. Pentasol: pentobarbial sodium powder, reconstitute in 250 ml=392 mg/ml Virbac
    3. Socumb
    4. Sleepaway Zoetis
    5. Sodium Pentobarbital (390 mg/ml) plus phenytoin sodium (50 mg/ml) →hastens cardiac arrest, so you can’t get high…you just die…humans are less likely to abuse
      • Euthasol
        • pH=12-13 (caustic!)
        • Thick, viscous
      • Beuthanasia-D: Merck Animal Health
      • Euthanasia III
    6. How sodium pentobarbital works in mammals 9
      Stage 1: voluntary excitement

      • Bloodstream → heart → cerebral cortex
      • Begins to lose consciousness/coordination, hyperesthesia, loses voluntary motor, loss of superficial pain → disorientation, possible movement

      Stage 2: involuntary excitement

      • Bloodstream → heart → cerebral cortex → cerebrum
      • Loss of consciousness → possible uncontrolled motor activity (paddling, vocalizations)

      Stage 3: surgical anesthesia

      • Bloodstream → heart → cerebral cortex → cerebrum → cerebellum (~5 seconds)
      • Cannot feel pain, doesn’t respond to visual/auditory, reflexes begin to disappear

      Stage 4: medullary paralysis

        • Bloodstream → heart → cerebral cortex → cerebrum → cerebellum
        • Depresses breathing, heartbeat, blood pressure→anoxia→brain cell death (~40 seconds) → possible heart

      fibrillation, agonal breaths, muscle spasms (unconscious, reflex)

    7. ROUTES of sodium pentobarbital administration: discuss the various routes it can be given, the pros and cons of each
      1. Sodium pentobarbital solutions are caustic and it can hurt if given in an inappropriate spot
        1. pH humane blood 7.35 13
        2. pH between 4.5-8 doesn’t hurt?
        3. pH 5-9 safe per some nursing place
        4. In vitro experiments have demonstrated that solution pH values of 2.3 and 11 kill venous endothelium cells on contact. 13
      2. Intravenous (IV) likely only after anesthesia because wild animals
      3. Intracoelomic likely only after anesthesia because wild animals 9, consider air sacs in avian and generally avoid 12
      4. Intracardiac only after anesthesia because painful
      5. Intraosseous and intramuscular, only after anesthesia because painful 12
      6. Intrahepatic only after anesthesia because requires careful placement and still animal12
      7. Per os, tastes bitter, but works well in gaping baby birds, prohibited in certain states 9
  3. WHAT IF DRUGS NOT AVAILBLE?Carbon dioxide:
    1. Rodents: recommendations changed = 30-70% of the chamber/cage volume/min (fill it faster?)
    2. Neonatal mice (that is, pups younger than 6 d) must be exposed to carbon dioxide (CO2) for as long as 50 min to achieve euthanasia.14
      1. Neonatal mice (n = 76; age, 1 or 2 d) were exposed to isoflurane in a sealed, quart-size (0.95-L) plastic bag at room temperature. Righting and withdrawal reflexes were absent in less than 2 min. After 30 min of exposure to isoflurane, pups were removed and monitored for recovery. All pups were cyanotic and showed no detectable signs of life when they were removed from the bag. However, after 30 to 120 min after removal from the bag, 24% of isoflurane-overexposed pups began gasping and then resumed normal respiration and regained a normal pink coloration. These results demonstrate that isoflurane overexposure at saturated vapor pressure for 30 min is insufficient to euthanize neonatal mice and that isoflurane overexposure must be followed by a secondary means of euthanasia.14
      2. → require extended exposure times 4
      3. Also true for newly hatched chickens (>5 min CO2 exposure) (rabbits and mink have prolonged survival times in CO2 as well)
    3. May cause distress in animals by 3 mechanisms (Leary) 2: (CO2 → respiratory acidosis)
      1. Pain due to formation of carbonic acid on respiratory and ocular membranes (pain starts at about 40% CO2 in people and apparently rats/cats
      2. Feeling of breathlessness → in humans, this starts at 8% and intensifies with higher concentrations
      3. Direct stimulation of ion channels with the amygdala associated with the fear response
    4. Exposure to CO2 does cause unconscious wing flapping in chickens (emotional observers)
    5. Slow rise in CO2 concentration creates less aversion
    6. Maintain CO2 flow for at least 1 min after respiratory arrest
    7. Do NOT use combustion (i.e. from a vehicle) or dry ice
    8. Preferably administered from compressed gas cylinders/tanks 15
    9. The use of volatile agent as induction to anesthesia before introducing CO2 to euthanize has been described.16,17
    10. PROS for CO2
      1. Rapid depressant, causes anesthesia at high concentrations in the blood
      2. Readily available in compressed gas cylinders, non-explosive, not controlled,
      3. Safe for people
      4. Remains can be fed to animals
    11. CONS for CO2
      • So many studies have conflicting results about aversion/breathlessness, within/among species, strains, breeds, etc. → no rule of thumb
      • Can/does cause aversiveness/distress
      • Heavier than air
      • Immature, aquatic, burrowing may have high tolerances for CO2
      • May take longer?
      • Need regulators/flow meters because if CO2 flows too quickly it will freeze

      Physical methods:

      • When properly used by skilled personnel with well-maintained equipment, physical methods of euthanasia may result in less fear and anxiety and be more rapid, painless, humane and practical than other forms of euthanasia“.4
      • Exsanguination, stunning and pithing should NOT be done w/o prior anesthesia
      • Aesthetics and humane can be in conflict, i.e. maceration for DOC → death is almost instantaneous
        • https://vimeo.com/174954377: video of day old chick maceration (will not show in presentation)—it appears horrible and visceral yet the amount of suffering is just a fraction of a second—probably the most humane euthanasia method for day old chicks
      • Blunt force trauma to head:
        • Appropriate for animals with thin craniums
        • Trained/proficient personnel, but personnel can/will become fatigued (physically, emotionally)
        • Strive for other options, this is a good last resort
        • DIFFICULT because of strength needed, resolve, knowledge of anatomy, only have one chance, thick skulls, needs resolve
        • not recommended by OIE (USDA, APHIS)18
      • Captive bolt: penetrating and non-penetrating
      • Gunshot: entire section in AVMA 2020 about gunshot, energy requirements, bullet selection, etc. bullet should go through cranium and into brain…firearm safety!19
      • Cervical dislocation
        • Hindlimbs one hand, head in the other, neck is hyperextended and dorsally twisted to separate the first cervical vertebrae from the skull—pull head and apply a ventrodorsal rotational force to the skull
        • Few studies that affirm the feeling that it is humane…”appears” to be humane
        • Small birds, poultry, waterfowl (birds < 3 kg)
        • Remain conscious ~1+ min after manual cervical dislocation 20
        • Four sources say poultry likely aren’t immediately unconscious 4 (we don’t know if consciousness and perception of pain are concurrent, but we do have to assume they are for now)
        • Pliers and other devices seem to prolong reflexes/time to death/etc.20 and are not recommended (Leary)4 → these crush the spinal cord/trachea and are not acceptable
        • Practice on dead things first
        • Blunt force trauma may be more humane ☹
        • Broomstick method, in hand method
      • Decapitation
        • Birds < 200g
        • Electrical activity in the brain persists for 13-14 seconds after, but other studies this does not necessarily mean pain is perceived
        • However, research has shown that in birds there may be some brain function for up to 30 seconds after decapitation 21, which makes this method unacceptable in welfare terms. Exsanguination without stunning is also unacceptable.
        • “Appears” to be humane but we don’t have enough studies
      • Exsanguination
        • Only after anesthesia/stunning b/c anxiety associated with extreme hypovolemia
        • Not as a sole method of euthanasia
      • Pithing: only have anesthesia
  4. BACK TO SONGBIRD CASE:
    1. Which method to use?
    2. Use chart to compare methods, routes, etc.
  5. GOOSE CASE:
    1. Physiologic components to discuss: breath holding in “diving birds”, large animal, thrashing

About the presenter

Renée Schott is the Medical Director and a Senior Veterinarian at the Wildlife Rehabilitation Center of Minnesota (WRCMN), one of the largest rehabilitation centers in the country. She has been involved in wildlife rehabilitation for over 15 years and has worked at WRCMN for over 8 years. Additionally, Renée is involved in teaching courses at the University of Minnesota-College of Veterinary Medicine and she is a Course Instructor for the International Wildlife Rehabilitation Council.

 

Webinar FAQ

Will I need special equipment to view and listen to a webinar?

All you need is a computer (or similar device) with an internet connection. Provided your computer has speakers (can you listen to music?) you will be able to view and listen to the webinar.

 

Additional questions or concerns?

Please contact LafeberVet at vetinfo@lafeber.com.

 

RACE approval

This program 776-41764 is approved by the American Association of Veterinary State Boards (AAVSB) Registry of Continuing Education (R.A.C.E.) to offer a total of 1.00 CE credits to any one veterinarian and/or 1.00 veterinary technician CE credit. This RACE approval is for Category Two: Non-Scientific Clinical using the delivery method of Non-Interactive-Distance. This approval is valid in jurisdictions which recognize AAVSB RACE; however, participants are responsible for ascertaining each board’s CE requirements. RACE does not “accredit” or “endorse” or “certify” any program or person, nor does RACE approval validate the content of the program.

 

References