Conker season is here. From late September, parks, greens and footpaths across Ireland and the UK are scattered with shiny brown horse chestnuts, and plenty of dogs find them irresistible to chase, chew and carry home. So, are conkers poisonous to dogs? Yes. Conkers contain a toxin called aesculin, and even one can make a dog unwell, while a whole conker can get stuck in the gut. Here is what to watch for, what to do if your dog eats a conker, and how to keep autumn walks safe.
Are conkers poisonous to dogs, and why?
Conkers are the seeds of the horse chestnut tree (Aesculus hippocastanum). The seeds, leaves, bark and spiky green cases all contain aesculin and related compounds called saponins, which irritate the lining of the stomach and gut. That is why most cases of horse chestnut poisoning in dogs show up as a bad bout of vomiting and diarrhoea.
The second danger is physical. A conker is hard, round and roughly the size of a walnut: exactly the right shape to lodge in the throat or block the intestine, especially in small and medium-sized dogs. A blockage is often more serious than the toxin itself, and it can take a day or two to show.
Symptoms of conker poisoning in dogs
Signs usually appear within one to six hours, but can take up to a day or more. Watch for:
- Vomiting, sometimes repeatedly
- Diarrhoea, which may contain blood
- Drooling and a sore, tender tummy
- Loss of appetite
- Restlessness or unusual tiredness
- Dehydration after repeated vomiting
If a conker is causing a blockage, you may also see straining, retching without bringing anything up, a hunched posture, or a dog that suddenly refuses food. Any of these needs a vet the same day.
What to do if your dog eats a conker
- Take whatever is left out of their mouth, calmly, so they don't gulp it down in a rush.
- Work out roughly how many they ate, and when. Note whether the conkers were whole or chewed into pieces, and take a photo or a sample if you're not sure what it was. Your vet will ask.
- Ring your vet straight away, even if your dog seems fine. Early advice matters, especially for small dogs or if a whole conker went down. If your practice is closed, call the out-of-hours emergency service.
- Don't try to make your dog sick at home. Salt water and other home remedies are dangerous, and bringing a hard conker back up can cause choking. If vomiting needs to be induced, your vet will do it safely.
- Keep a close eye on them for the next 48 hours, even once any sickness settles: check they're eating, drinking and passing stools normally.
The good news is that, with prompt treatment, most dogs recover fully within a few days. Fatal cases are rare.
What about acorns and sweet chestnuts?
Conkers aren't the only autumn hazard underfoot. Acorns contain tannins that can cause stomach upset and, in large amounts, kidney damage; the green, unripe ones that fall early in the season are generally considered the most harmful. Sweet chestnuts, the kind roasted at Christmas markets, aren't toxic, but their spiky cases can injure mouths and paws, and a whole nut is still a choking risk.
Telling them apart is easy once you know: conkers are glossy and rounded and grow in a green case with a few short, blunt spikes, while sweet chestnuts have a pointed tip and grow in a case covered in dense, needle-like spines.
How to keep your dog safe during conker season
- Know where the trees are. Horse chestnuts are common in parks, school grounds and along tree-lined roads. Until the last conkers have fallen, usually by late October, avoid those stretches or walk them on the lead.
- Teach a solid "leave it" and "drop". Practise at home with low-value items and reward with something better. A dog that will happily swap a conker for a treat is far safer than one you have to chase.
- Clear your own garden. If you have a horse chestnut or an oak, rake up fallen conkers and acorns every few days while they're dropping.
- Keep conkers brought indoors out of reach. That includes the kids' conker collection and any left on windowsills as a spider deterrent.
- Consider a basket muzzle for persistent scavengers. A well-fitted one lets a dog pant and drink but stops them picking things up. Introduce it gradually, with treats.
Give the scavenging instinct a safer outlet
Many dogs hoover up conkers simply because sniffing out and finding food is deeply rewarding for them. You won't cure a scavenger overnight, but giving that foraging urge a regular outlet at home can take the edge off. Scatter part of their dinner on the lawn for a sniff-and-find game, or serve meals in a slow feeder bowl, which turns a 30-second gulp into a few minutes of work. Combine that with a well-practised "leave it", and autumn walks become much less of a battle.
If your dog does eat a conker, call your vet rather than waiting to see what happens.