By Dial A Vet Veterinary Team
A dog that hoovers up a walnut dropped from a salad is usually fine. A dog that spends an autumn afternoon eating old walnuts under a backyard tree can end up at the emergency vet with full-body tremors. The difference is mould. Walnuts are not toxic in themselves, but they are prone to growing moulds that produce tremorgenic mycotoxins, and they are large, hard and fatty, which brings its own problems. Walnuts are best left off your dog's menu.
Key takeaways
- Fresh, plain, shelled English walnuts are not classed as toxic to dogs, but they are high in fat and not a good treat.
- Mouldy walnuts, often found on the ground under trees, can contain tremorgenic mycotoxins such as penitrem A, which cause tremors and seizures.
- Black walnuts and their hulls are more often linked with mould problems.
- Whole walnuts and shells can cause choking or gut blockages, especially in small dogs.
- Salted, sugared, chocolate-coated or spiced walnuts add further risks.
- Related: nuts that are toxic to dogs, autumn hazards for dogs, intestinal blockage in dogs.
Fresh walnuts
English walnuts are the kind sold in supermarkets and grown in parts of Tasmania, Victoria and New South Wales. They are not known to contain a specific toxin for dogs. But they are:
- High in fat. A handful is a lot of fat for a small dog and can cause vomiting, diarrhoea or, in some dogs, pancreatitis.
- Large and hard. Dogs tend to swallow nuts whole. A whole walnut or a piece of shell can lodge in the throat, oesophagus or intestine.
- Often flavoured. Candied, honey-roasted, salted or chocolate-coated walnuts bring sugar, salt or theobromine into the picture.
There is no nutritional reason to feed walnuts to a dog.
Mouldy walnuts: the real danger
Walnuts that sit on damp ground, or stay in a pantry for too long, can grow moulds such as Penicillium species. Some of these produce tremorgenic mycotoxins, including penitrem A and roquefortine. These toxins act on the nervous system and can cause signs within 30 minutes to a few hours:
- Vomiting
- Restlessness, panting or agitation
- Fine trembling that progresses to severe whole-body tremors
- Wobbliness
- Sensitivity to noise and touch
- High body temperature
- Seizures
Cases have been published from the United States and New Zealand, including a New Zealand dog that ate walnuts left on the ground for months. The same mycotoxins are found in mouldy food in bins and compost, so a walnut tree is not the only source.
Black walnuts
Black walnuts (Juglans nigra) are less common in Australia than English walnuts but are grown in some gardens and parks. Their thick green hulls go black and mouldy as they rot, and dogs that chew them are at risk of mycotoxin poisoning and stomach upset. Black walnut wood shavings are also known to cause laminitis in horses, so they should not be used as horse bedding.
Signs of a blockage
- Repeated vomiting, especially after eating or drinking
- Refusing food
- Belly pain or a hunched posture
- Straining with little or no faeces
- Lethargy
When it is an emergency
Go to a vet straight away if your dog ate fallen, old or mouldy walnuts, or walnut hulls, even before signs appear. Also seek urgent care for tremors, seizures, a high temperature, repeated vomiting, choking or belly pain. Do not try to make your dog vomit at home, as tremoring dogs can inhale vomit. The Animal Poisons Helpline on 1300 869 738 can advise.
How vets treat it
For recent mouldy nut exposure in a dog without signs, your vet may induce vomiting and give activated charcoal. Dogs with tremors may need sedation and muscle relaxants, intravenous fluids, cooling and close monitoring. Most dogs recover within a day or two with prompt treatment, though severe cases need intensive care. A suspected blockage is investigated with X-rays or ultrasound and may need endoscopy or surgery.
Prevention
- Rake up fallen walnuts regularly in autumn and keep dogs out of the area under walnut trees.
- Throw out old or mouldy nuts in a sealed bin.
- Keep compost and food waste bins dog proof.
- Store nut mixes and baking supplies in closed cupboards.
FAQ
My dog ate one fresh walnut from the bowl. Is that okay?
One fresh, plain walnut is unlikely to cause harm in a medium or large dog. Watch for vomiting or signs of a blockage, and call your vet if your dog is small.
Are walnuts as dangerous as macadamias?
No. Macadamias cause weakness and wobbliness in dogs even when fresh. Walnuts are mostly a risk when mouldy or swallowed whole.
Is walnut oil safe?
It is not toxic, but like any oil it is high in fat and can upset the stomach.
What about walnut pesto or banana bread with walnuts?
These often contain garlic, onion, sugar or raisins. Keep them away from your dog.
Talk with a vet
If your dog has been eating walnuts under a tree or seems shaky after raiding the bin, a Dial A Vet veterinarian can help you decide how urgent it is. Book a Dial A Vet consult.
References
- Richard JL, Bacchetti P, Arp LH. Moldy walnut toxicosis in a dog, caused by the mycotoxin, penitrem A. Mycopathologia. 1981;76:55-58.
- Munday JS, et al. Presumptive tremorgenic mycotoxicosis in a dog in New Zealand, after eating mouldy walnuts. N Z Vet J. 2008;56(3):145-147.
- Pet Poison Helpline. Moldy food.
- Animal Poisons Helpline (Australia). 1300 869 738.
Disclaimer: Educational only. This page does not replace an examination or advice from your own veterinarian. If you are worried about your pet right now, contact your local vet or nearest emergency animal hospital.