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Oak Poisoning, Tannin Toxicosis
Acorn toxicosis occurs in many animal species, caused by ingestion of hydrolyzable tannins contained within oak twigs, buds, leaves and acorns. There are over 500 different species of oak (Quercus spp) trees worldwide, with 70 of them found in North America. All species are considered to be toxic to animals. Oaks are classified into multiple groups according to their leaf color--red, black and white oaks. Black and red oak species have been reported to contain higher amounts of tannins then others.
Green acorns and budding leaves contain the highest levels of tannins, which is why most cases of poisoning in animals occur in the spring and fall. Fallen acorns will remain toxic for several months after falling from trees. Tannins have protein-binding properties, and are known to inhibit several digestive enzymes, including proteases, pectinases, amylases, cellulases, and lipases. When ingested by ducks, the tannins, as well as their metabolites, can cause severe gastrointestinal damage, kidney dysfunction, and possibly mechanical obstruction.
Most of the time, signs of poisoning occur several days following when oak parts were first eaten by ducks. If diagnosis and treatment are delayed, it often leads to severe kidney and liver damage which can be fatal. The only treatment for ducks with suspected acorn toxicosis is prompt recognition of the problem, supportive care, and diuresis to aid in clearing the toxins from the duck's system.
Ducks don't normally have a preference for eating acorns, and if they are well fed acorn toxicity is generally not a problem. However, sometimes there is an occasional duck that likes acorns, and will actively seek them out to eat. Some ducks can eat acorns without any problems, however others develop signs of poisoning.
Case 1: Acorn toxicosis in a Duck An adult male, white duck presented as an emergency to the Zoo, Exotic and Wildlife Medicine Service of the Boren Veterinary Medical Teaching Hospital, Center for Veterinary Health Sciences, Oklahoma State University. The patient was reported to have a 7-day history of progressive inappetence, lethargy, and isolation from its flock. The patient was part of a mixed-species waterfowl flock residing on a public pond. The pond was routinely maintained, and the ducks were fed a commercial seed mixture three times weekly. Additionally, the ducks forage, eating a variety of plant materials and foliage as well as foods provided by visitors to the pond. The ducks had regular human contact and were reasonably social. Located in a public park, the pond was surrounded by oak trees (Quercus spp), cypress trees (Cypressus spp), grass, concrete walkways, and rocky substrate. The grounds crew had noticed the duck had not been feeding or socializing normally and had decreased buoyancy. The grounds crew caught the duck and brought it to the Veterinary Teaching Hospital for care. On presentation, the duck was markedly weak, lethargic, and easily stressed by physical restraint. A cursory physical examination most notably revealed the crop to be markedly distended and firm. With handling, the duck regurgitated rancid seeds and plant materials. The duck was water-soaked through to its down feathers, indicating a lack of waterproofing, which surely contributed to decreased buoyancy and suspected hypothermia. The duck was emaciated (body condition score: 1/5; body weight: 1.7 kg), suggesting a chronic condition. The duck appeared to be in shock (i.e., pale, mildly cyanotic mucous membranes; a slow capillary refill time) and was estimated to be 10% dehydrated (e.g., tacky mucous membranes). Ref