Why Black Walnuts Is Dangerous for Dogs
Black walnuts (Juglans nigra) contain juglone, a naphthoquinone compound found primarily in the hulls, bark, and roots. Juglone is known to be toxic to horses and has been reported to cause GI upset and neurological symptoms in dogs. However, the greater danger from black walnuts is tremorgenic mycotoxins — specifically penitrem A and roquefortine C — produced by molds (Penicillium spp.) that commonly grow on fallen walnuts. These mycotoxins cause severe neurological symptoms: whole-body muscle tremors, seizures, hyperthermia, and potentially death. Dogs are often exposed when they find and eat fallen black walnuts that have been on the ground long enough to develop mold. Moldy English walnuts can pose the same mycotoxin risk, though English walnuts do not contain juglone.
Toxicity Profile of Black Walnuts
Black walnuts (Juglans nigra) contain juglone, a naphthoquinone compound found primarily in the hulls, bark, and roots. Juglone is known to be toxic to horses and has been reported to cause GI upset and neurological symptoms in dogs. However, the greater danger from black walnuts is tremorgenic mycotoxins — specifically penitrem A and roquefortine C — produced by molds (Penicillium spp.) that commonly grow on fallen walnuts. These mycotoxins cause severe neurological symptoms: whole-body muscle
Safe Serving Size by Dog Weight
| Dog Size | Safe Amount | Frequency |
|---|---|---|
| Small (under 10 kg / 22 lbs) | NONE | Never |
| Medium (10-25 kg / 22-55 lbs) | NONE | Never |
| Large (25+ kg / 55+ lbs) | NONE | Never |
NONE — combination of juglone toxicity and mold mycotoxin risk makes all walnuts inadvisable
How to Prepare Black Walnuts for Dogs
If black walnut trees grow in your yard or neighborhood, regularly rake and dispose of fallen nuts in sealed containers. Do not compost them where dogs can access the pile. Even nuts that appear clean may harbor mold within the hull. English walnuts are less toxic but still high in fat and prone to mold. No type of walnut is recommended for dogs.
Warning Signs and Symptoms to Watch For
Mycotoxin poisoning (most common): whole-body muscle tremors that worsen with stimulation, generalized seizures, hyperthermia, vomiting, weakness, ataxia (loss of coordination), and in severe cases, respiratory failure. Juglone toxicity: vomiting, diarrhea, and GI irritation. Symptoms typically appear within 1-4 hours of ingesting moldy walnuts.
What to Do If Your Dog Ate Black Walnuts
Contact your vet immediately. Treatment for mycotoxin tremors includes methocarbamol (muscle relaxant), diazepam for seizures, IV fluids, cooling measures for hyperthermia, and activated charcoal if ingestion was recent. Most dogs recover within 24-48 hours with appropriate treatment. Bring a sample of the walnuts if possible.
Breed-Specific Note
No specific breed predisposition has been identified for walnut toxicity. All sizes and breeds are equally at risk, with smaller dogs needing fewer nuts to reach toxic doses.
Frequently Asked Questions
Are regular (English) walnuts also dangerous for dogs?
English walnuts do not contain juglone but can still harbor tremorgenic mold, especially if stored improperly or found on the ground. They are also very high in fat (65g per 100g), posing a pancreatitis risk. No walnuts are recommended for dogs.
Why are black walnuts specifically toxic to dogs?
Black walnuts contain juglone, which is toxic to dogs and horses but not to most other animals. Additionally, black walnut hulls are particularly prone to Penicillium mold colonization, which produces tremorgenic mycotoxins. The combination of chemical and biological toxins makes black walnuts doubly dangerous.
My dog plays in a yard with a black walnut tree — is that a risk?
Yes. Dogs frequently pick up and chew fallen walnuts, which may be moldy even if they look intact. Regularly clear fallen nuts from the yard. The hulls staining the ground dark brown is a sign juglone is present. Some dogs also develop contact dermatitis from black walnut hull compounds.
Can walnut mold mycotoxins affect humans too?
Yes, though humans are less sensitive. Penitrem A and roquefortine C can cause neurological symptoms in humans who eat heavily moldy nuts, though cases are rare because people rarely eat visibly moldy food. Dogs are more vulnerable because they eat found items without discrimination.
How can I tell if a walnut is moldy enough to be dangerous?
You often cannot tell by visual inspection alone — mold can be present within the hull before visible surface growth appears. Any walnut that has been on the ground, feels soft or damp, has a musty smell, or shows visible mold should be considered dangerous. The safest approach is to keep all walnuts away from dogs.
Sources: American Kennel Club · ASPCA Animal Poison Control · PetMD · Merck Veterinary Manual.