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

Sodium pentobarbital is a veterinary drug commonly employed to euthanize different animal species humanely. Cases of secondary pentobarbital poisoning have been documented in scavenging wildlife, companion animals and captive carnivores. Since the extent of such poisonings remains mostly unknown, a review was undertaken to consolidate cases published, recorded, only locally reported or shared anecdotally. A questionnaire was distributed to veterinary surgery and wildlife rehabilitation centers, and zoos. About 125 cases affecting 432 animals across the US, Canada, the UK, South Africa, New Zealand, Australia, Germany and France were collated, with 76.8% obtained outside the published literature. Our findings support that pentobarbital poisoning affects a range of wild species (e.g., griffon vultures, canids) and companion animals (especially dogs and captive carnivores), and although a known source of toxicosis, pentobarbital-related poisonings continue to present day. Carcass disposal methods were considered in regard to associated incidents of secondary poisoning. Wild scavengers and companion animals were mainly affected after feeding on livestock carcasses that were insufficiently buried or left uncovered. 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 emerged as noteworthy sources of risk or exposure. The ongoing presence of pentobarbital residues in pet food as a threat to companion animals was incidentally considered. Additional recommendations for follow-up research, to increase awareness of this issue and prevent exposure, were suggested.