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Research review: A review of secondary pentobarbital poisoning in scavenging wildlife, companion animals and captive carnivores

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Griffon Vulture feeding (c) Bruno Berthemy

Vultures face multiple threats and secondary poisoning is one of the most serious. If animals that are euthanized with veterinary drugs (e.g. sodium pentobarbital) and are not disposed of sufficiently and responsibly, it might negatively affect other animals through intoxication. This is the case when scavengers like vultures or even companion animals like dogs feed on carcasses euthanized with vet products and get poisoned, leading to death in most cases. A research conducted by Kathleen Wells, Andrew Butterworth and Ngaio Richards, reviews the problem of pentobarbital poisoning to gain a deeper understanding of the extent of the issue and help raise awareness among relevant stakeholders. 


Pentobarbital poisoning affects a range of wild species (e.g., Griffon Vultures, canids) and companion animals (especially dogs and captive carnivores). Although a known source of toxicosis, pentobarbital-related poisonings continue to be present today.

This review was launched to gather information and expand upon current knowledge to generate further awareness of this issue. It focused on the range of poisoned species, current carcass disposal and provision practices, and the level of knowledge of the problem among animal practitioners and caregivers.


The review comprised 1) a collation of secondary pentobarbital poisoning records from existing publications and 2) questionnaire sampling of veterinary surgical and wildlife rehabilitation centres, and zoos. 

Informal, personal discussions and interviews with relevant experts and members of conservation organizations (e.g., BirdLife) were also conducted.


Cases were documented from the UK, the US, Canada, South Africa, New Zealand, Australia, Germany and France. An estimated 125 cases (1967 through 2017) affecting a total of 432 animals were collated – of these, only 29 cases came from the published literature.

Wild scavengers and companion animals were mainly affected after feeding on livestock carcasses that were insufficiently buried or left uncovered. In 79% of the estimated 125 poisoning cases the euthanized animal carcasses were domestic livestock species. The livestock carcasses that were most common at the root of poisoning cases were: sheep (Ovis aries; 35%), horses (Equus caballus; 28%) and cattle (Bos taurus; 24%).

Captive carnivores were accidentally poisoned after being fed pentobarbital-euthanized animals. Euthanized carcasses of stranded whales, provision of euthanized carcasses to dogs at hunt kennels, sourcing of meat from fisheries and laboratories, and use of barbiturates in baits to deliberately harm wildlife also emerged as noteworthy sources of risk or exposure.

Most of the wild animals reported as having been poisoned by pentobarbital were scavenging bird species, 86% involving species in the eagle family (Accipitridae), with 73% of cases affecting Bald Eagles. Other affected species included Griffon Vultures, Red Kites and Wood Storks. 

Eight methods for disposing of euthanized animal carcasses were identified including: placement outside uncovered, burial and disposal at landfill, incineration, rendering and burning. The feasibility of implementing various disposal options varies geographically.

Discrepancies exist in the interpretation of what constitutes a ‘safe’ burial depth within the associated standards and guidelines, with underlying assumptions often made that risks are being managed somewhere along the chain of supply or disposal. No specific burial depth requirements for euthanized animal carcasses have been collectively discussed or agreed between members of the veterinary and animal care community, municipal or landfill managers, wildlife protection agents, and other key stakeholders.

Presently, neither debilitated living animals or carcasses are typically screened for pentobarbital residues routinely or opportunistically, nor is there a centralized database to monitor or, where applicable, link occurrence of pentobarbital poisoning incidents. The absence of screening and monitoring is noteworthy because wild animals may feed on a tainted carcass then disperse, reducing their likelihood of discovery, particularly in remote areas. Without a centralized database, such solitary deaths or cases of debilitation may go undetected, fail to be attributed to pentobarbital exposure, or fail to be tallied as part of or linked to a more widespread incident of poisoning.

Through this research, the authors also demonstrated that cases in which animals are determined to have been exposed to pentobarbital but recovered with treatment might not be reported as such or further investigated.

The deliberate use of pentobarbital as a poisoning agent, via bait material laced with the drug, has been documented in Spain. Notwithstanding that to date only a single case has been uncovered, this discovery should be sufficiently compelling to instigate routine monitoring.


Based on the information gathered during this review, the following recommendations are made:

  1. Continued development of standardized guidelines for euthanized animal carcass management and disposal
  2. Increased dissemination of information on the risks of pentobarbital poisoning to multiple stakeholders, with the promotion of information-sharing and interfacing between all stakeholders
  3. Increased caution towards carcasses for animal consumption, supported by standardized guidelines on safe sourcing and provision
  4. Individual scrutiny of regulations and safety standards currently in place around the rendering of euthanized animal carcasses and the incorporation of rendered by-products into pet food products
  5. Separate review and investigation of pentobarbital (and other barbiturates) exposure and poisonings in pet food products
  6. Further investigation of any risks that other barbiturate and euthanasia drugs may have to companion animals, scavenging wildlife and captive carnivores
  7. Inclusion of pentobarbital (and, as applicable, other euthanasia drugs) in routine toxicological monitoring and opportunistic screening of all suspected poisoned animal cases


Wells, Butterworth & Richards (2020). A review of secondary pentobarbital poisoning in scavenging wildlife, companion animals and captive carnivores. Journal of Veterinary Forensic Sciences, 1(1), 1-15.

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