Secondary Barbiturate Toxicity in Bald Eagles and a Red-Tailed Hawk
Secondary toxicity is a relatively common occurrence in free-ranging carnivores and scavengers, particularly in raptors. Secondary toxicity had been documented in a variety of wildlife in BC, including barbiturate toxicity in eagles (Hayes, 1988). In early 2019, seven bald eagles and a red-tailed hawk were submitted to the BC Ministry of Agriculture Animal Health Centre in Abbotsford, BC, after all being found dead within a small geographic area. They were suspected to have had access to a domestic sheep that had been recently euthanized.
On gross examination of the carcasses, all birds were in excellent body condition. There were no obvious signs of disease or trauma, and all birds had distension of the crop and stomach, which were filled with abundant material consistent with sheep muscle, bone and soft tissue. There were no significant findings on microscopic examination of the tissues. Samples of liver and stomach contents were sent to an external laboratory for toxicological testing; GC/MS revealed traces of pentobarbital in all submitted samples. Pentobarbital is a barbiturate that is commonly used as an animal euthanasia agent.
This case highlights some of the typical findings in cases of secondary toxicity in wildlife. A large number of animals that die in a small location and multiple species affected in one incident are highly suspicious of a toxicity. In addition, animals dead from toxicity are often in good body condition and have abundant feed in the digestive tract, presumably with the feed material that contains the toxin.
It is unclear whether the sheep carcass was left out intentionally or not in this case, but the outcome still emphasizes some key points in prevention of secondary toxicity. When euthanizing any animal, the carcass should be disposed of appropriately and promptly, as it can be a source of toxicity for a wide range of species, often even after the carcass had been in the environment for an extended period of time and undergone decomposition. Veterinarians disposing of animals euthanized in the clinic should also inform landfills of disposal to allow for immediate covering of the carcasses with waste material. In addition, carcasses known to be laced with toxins should not be intentionally left out for pest animals (e.g., coyotes, raccoons, etc.) to consume, as other animals also have access and the main species affected are often not the target species.
Hayes, B. British Columbia: Deaths caused by barbiturate poisoning in bald eagles and other wildlife. Canadian Veterinary Journal 1988; 29(2): 173–174.
Dr. Tony Redford
BC Ministry of Agriculture Animal Health Centre