Acorns and horse chestnuts are not safe for dogs to eat. Both contain compounds that irritate the stomach and intestines, and both are the right size and shape to lodge in a dog’s gut. Vomiting, repeated retching, belly pain, lethargy or refusing food after a walk under oak or chestnut trees all warrant a call to your veterinary team.
Why late August starts windfall season in Guildford
The first acorns come down well before the leaves turn. In this part of Surrey, oaks and horse chestnuts begin dropping through late August, and the fall accelerates through September and October with every windy day. Green, unripe acorns land first, and those are the ones with the highest concentration of the compounds that cause trouble.
Guildford makes this a daily walk problem rather than an occasional one. The older residential streets north and south of 104 Avenue are lined with mature broadleaf trees, the boulevards along 148 Street carry long runs of them, and the park and greenway edges around the neighbourhood collect windfall in exactly the places dogs like to sniff. A dog that walks the same block twice a day in September passes under a lot of loaded branches.
The pattern we hear about most is the young dog who has never shown interest in anything on the ground suddenly hoovering up a mouthful of something crunchy. Puppies and adolescent dogs explore with their mouths, and a hard, rattling nut that rolls when nosed is an appealing object. Labradors and other retrieving breeds are heavily represented, simply because carrying things is what they were bred to do.
What is actually in an acorn
Acorns and oak leaves contain tannins, a group of plant compounds that bind to proteins in the digestive tract. In small quantities they are irritating. In larger quantities, or with repeated snacking over days, they can inflame the stomach and intestinal lining and, in more serious cases, affect the kidneys and liver.
Three things push a case from mild to significant: how many were eaten, how green they were, and how big the dog is. A forty kilogram dog that crunches one ripe acorn is in a different situation than a small terrier that spends ten minutes eating green ones under a tree. Unripe acorns carry more tannin than the brown ones that have been on the ground for weeks.
Signs usually appear within a few hours to a day. Vomiting and diarrhoea come first, often with drooling, a tucked-up posture, or a dog who stands with the front end down and the back end up because the belly is sore. Some dogs simply go quiet and refuse breakfast, which is easy to miss.
Conkers are a different problem
Horse chestnuts, the glossy brown conkers that come out of spiky green husks, are not the same as the sweet chestnuts sold for roasting. They contain aesculin, which causes marked stomach upset and, in some dogs, wobbliness or unusual dullness alongside the vomiting.
Conkers bring a mechanical risk that acorns share but conkers exaggerate: they are round, dense and roughly the width of a small dog’s intestine. A conker that goes down whole does not always come back up, and it does not break down. The spiky husk is worth watching too, since dogs occasionally mouth those and end up with punctures to the tongue, gums or palate.
The obstruction risk owners underestimate
Most owners think about poisoning first. In practice, the blockage is often the bigger concern, and it is the one that develops quietly over a day or two rather than announcing itself in the first hour.
An intestinal obstruction stops food and fluid moving through. The classic pattern is repeated vomiting that will not settle, especially vomiting that continues when the stomach is empty, along with a painful abdomen, a dog who cannot get comfortable, no stool being passed, and progressive flatness. This is an assessment that needs hands and imaging, not a wait-and-see approach at home. Our diagnostic imaging lets the team see whether something is sitting where it should not be, and if surgery is needed, our surgical services team can act on that quickly.
Signs worth a call after an autumn walk
- Vomiting more than once, or retching that brings nothing up
- Diarrhoea, particularly if it is dark or contains blood
- Refusing food, or eating far less than usual
- A tense, tucked-up or painful belly, or a stretched praying posture
- Drooling, lip licking or repeated swallowing
- Unusual quietness, hiding, or reluctance to move
- Straining without producing stool
- Any wobbliness or weakness
If you saw your dog eat acorns or a conker, do not wait for signs to appear. Phone and describe roughly how many, how big your dog is, and when it happened, and our team can advise whether your dog needs to be seen. Never give anything at home to try to bring it back up. That decision belongs to a veterinarian, because doing it at the wrong moment or with the wrong substance can cause more damage than the nut. This is exactly the sort of case our urgent care service exists for.
The rest of the early-autumn windfall
Acorns and conkers get the attention, but the same walks turn up other things worth steering a dog away from. Windfall apples and plums ferment on the ground and the stones can obstruct. Walnuts and their husks go mouldy quickly on damp ground. Piles of raked leaves collect all of the above in one convenient heap at nose height.
Cats are far less often affected. They are selective eaters and rarely chew hard plant material, though a curious kitten may bat a conker around and occasionally mouth one.
Practical steps for Guildford walks
Look up as well as down. Once you know which trees on your regular route are dropping, you can cross the road for that stretch through September and October. A short lead under those trees, rather than a loose extendable, keeps your dog’s head out of the gutter line where windfall gathers.
Teach and reward a solid “leave it” before the season peaks, and carry something better than an acorn so the trade is worth making. In your own garden, sweep regularly rather than seasonally, and clear windfall before it accumulates. If your dog is a determined scavenger, a basket muzzle used kindly and with proper introduction is a reasonable tool for a few weeks of the year.
Dogs who scavenge habitually are also worth a conversation about why. Sometimes it is boredom or adolescence, and sometimes an unsettled appetite has a medical driver worth investigating during a medical assessment. Our article on why vomiting or diarrhea is not always just a stomach bug covers the signs that a settled tummy upset is something more, and our guide to what to do if your dog eats something toxic is worth reading before you need it. If you are unsure how urgent a situation is, our overview of urgent care signs in dogs gives you a clear threshold.
Frequently asked questions
Are acorns poisonous to dogs?
Yes, acorns are considered toxic to dogs. They contain tannins that irritate the digestive tract, and in larger amounts can affect the kidneys and liver. Green, unripe acorns carry more tannin than old brown ones. The amount eaten and the size of the dog both matter, so call your veterinary team rather than judging severity at home.
How many acorns would make a dog sick?
There is no safe number that applies to every dog. A single acorn in a large dog may cause nothing at all, while a handful in a small dog can cause significant stomach upset, and even one conker can lodge in the gut. Because size, ripeness and quantity all interact, any known ingestion is worth a phone call.
My dog swallowed a conker. What should I do?
Phone the clinic straight away and describe your dog’s size and when it happened. Horse chestnuts cause stomach upset and are a real obstruction risk because of their shape and density. Do not try to make your dog bring it up at home. Keep them calm, withhold further food until you have spoken to the team, and watch for repeated vomiting or belly pain.
How long after eating acorns would a dog show signs?
Digestive signs usually start within a few hours and often within the first day. An obstruction can be slower and may only become obvious after twenty four to forty eight hours, which is why persistent vomiting a day later still deserves attention. If you know something was eaten, watch closely for two full days.
Are acorns dangerous for cats too?
The compounds are the same, but cats rarely eat acorns because they do not chew hard plant material the way dogs do. Kittens sometimes play with conkers and may mouth one. If you see a cat chewing or swallowing either, treat it the same way you would with a dog and get in touch.
What about mouldy fallen fruit under the trees?
Windfall that has been on wet ground for a while can grow moulds, and some of those produce substances that affect the nervous system as well as the gut. Tremors, twitching or unsteadiness after a walk in an area with rotting fruit is a same-day concern. Clearing windfall from your own garden regularly removes a good part of the risk.