Merck Manual

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Pet Owner Version

Quercus Poisoning (Oak Bud Poisoning, Acorn Poisoning)


Barry R. Blakley

, DVM, PhD, Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan

Reviewed/Revised Oct 2020 | Modified Nov 2022

Most animals are susceptible to Quercus poisoning, and most species of oak in Europe and North America are considered toxic. Signs occur several days after eating large quantities of young oak leaves in the spring or green acorns in the fall. The death rate is often high. Malformed foals and abortions have been reported in mares consuming acorns during the second trimester of pregnancy. The toxin causes gastrointestinal and kidney problems. Signs include loss of appetite, depression, weight loss, dehydration, urgent and painful defecation, smell of ammonia on the breath, clear discharge from the eyes or nose, excessive thirst, passing large amounts of urine, blood in the urine, jaundice, and constipation followed by slimy or bloody diarrhea.

Feeding a pelleted ration supplement containing 10 to 15% calcium hydroxide plus providing access to more palatable feeds can be used as a preventive measure if exposure to acorns or oak leaves cannot be avoided. Calcium hydroxide and purgatives (such as mineral oil, sodium sulfate, or magnesium sulfate to aid in passing of feces) may be effective if given early in the course of disease. Fluid treatment may be beneficial. Recovery usually occurs within 60 days but is rare if kidney damage is severe.

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