What Should I Do If My Dog Ate A Small Piece of Onion?

It is good to know that you are aware of how dangerous eating onions can be for a dog- this saves us some time!

In this situation, you have two options.

And each option requires you to act swiftly and decisively.

If you are certain that it was only a small amount of onion, you might want to do a quick calculation to work out if your dog ate enough onion for it to be toxic.

For this you need the amount (weight) of the onion they ate and the weight of your dog.

I explain it in more detail below.

And the second option, is your head is in too much of a spin, is to phone your vet.

But the vet will probably want to know the same information…

But what is it about onions that makes them so problematic?

Why is onion toxic?

Onion is toxic to dogs because of a chemical called n-propyl disulphide.

Whereas this isn’t toxic for humans (because our body can absorb it) in big enough amounts it can kill a dog.

A dog cannot process or absorb n-propyl disulphide.

And so it attaches itself to the outside of red blood cells within a dog’s body causing them to explode.

Now red blood cells are the ones that carry oxygen around the body and so they can’t be mucked around with.

But as a dog eats more onions, the concentration of n-propyl disulphide increases in their body and the more red blood cells that are destroyed.

If your dog isn’t treated by a vet, they will become anaemic and they will eventually be starved of oxygen and die.

How many onions will kill a dog?

The one positive element in all of this is that onions don’t kill dogs on sight or “on sniff.”

A dog needs to ingest a certain amount of onions and the exact amount of onion changes with the size of the dog.

Bigger dogs have a higher tolerance of onions than smaller dogs.

So if a Chihuahua, Labrador and Great Dane were all to eat a few slices of onion then the Chihuahua would be in much greater danger than the Labrador or the Great Dane.

Another piece of good news is that you can roughly work out your dog’s tolerance level for onions.

And by this I mean the amount (by weight) of onion that your dog can safely eat before it sends them over the edge.

And by using the phrase safely eat I’m not encouraging you to add onion to your dog’s diet (as you shouldn’t), I’m only pointing out that every dog has a margin of safety. 

The best formula to use is to say that your dog can eat up to .5% of their body weight in onions before the levels of n-propyl disulphide become so high that your dog will need urgent medical attention. 

And when I first looked at this, I thought “wow, that’s a lot of onions!”

By having done the calculations, particularly for smaller dogs, I’m thinking “wow, that’s frighteningly small.”

Let’s think about a 2.5 kg (5.5 lbs) Chihuahua.

.5% of their body weight is 12g.

And so eating 12g of onion is their safe limit.

And 12g is nothing, particularly when it is mixed in with a tasty bit of spag bol that they’ve just shared with their owners. 

My step daughter has a French Bulldog, which weighs around 25 pounds or 12.5 kg.

Now he can eat around 60 g of onion before he puts himself in any danger.

But that is still a tiny amount.

We have some very small onions in our cupboards at the moment- they are slightly bigger than a golf ball. 

But one of those onions still weighs 40 g!

Symptoms of onion poisoning in dogs

So, by accident, your dog has eaten some onions.

What symptoms should you be vigilant for?

Onion poisoning often starts by making your dog look and feel sick.

So this is your vomit, diarrhea, sore to the touch tummy and that general lethargy.

But over a couple of days, the symptoms shift as your dog’s red blood cells come under attack. 

At this stage, you might see that your dog is panting far more than usual, their gums are much paler and their heart is beating incredibly quickly- whilst all they can do is lie on their bed looking at you.

Realistically, you need to get in touch with your vet as soon as you see the early signs of a stomach upset.

Don’t wait for the panting and rapid heart beat because by then it could be too late. 

Two forms of onion poisoning

Now there are two ways to poison your dog with onions.

The first way is to poison them all at once- this is when their body has a massive overdose.

Going back to the Chihuahua this could mean that they most of the pan of a spag bol that was left out overnight.

The second way is to poison them slowly over a few days.

This is when the body doesn’t take one massive hit of n-propyl disulphide.

But by eating a relatively large amount of onions over a few days, the toxin gradually builds in your dog’s body until it starts to attack those red blood cells. 

I’m struggling to picture how this might happen but it could be something like drip feeding your dog leftover cottage pie over the space of a few days…

Treatment of onion poisoning in dogs

Once your dog is at the vets, at least you know that they are in the hands of the experts. 

Your vet will probably run some blood tests to find out what is happening to the red blood cells and oxygen levels.

And they might try and give your dog some activated charcoal via a tube.

Charcoal should absorb the toxin by taking it out of the blood. 

And if you were quick off the mark and headed to the vets soon after your dog snacked on the onion, your vet might try and induce vomiting. 

Dog friendly vegetables

If your dog ate some onion because you fed it to them and you had no idea how dangerous they are, it might be a good idea to talk about alternatives.

And the list is almost endless as long as you stay away from garlic, tomatoes and asparagus.

You can add vegetables to your dog’s diet as snacks (instead of those lifeless dog biscuits) or as part of their main meal.

Vegetables add variety to your dog’s eating experience- particularly in terms of taste and texture.

And remember, they also can provide a nice boost in vitamins and minerals.

Apart from the variety that comes from there being so many vegetables to choose from, they also add variety in the way that they can be fed to your dog- raw, cooked or sometimes even frozen. 

And there is a lot of unnecessary waste when it comes to preparing vegetables- think of the skins that we peel, the leaves that we cut off or the stalks that we discard.

Most of this is highly nutritious and can be upcycled by being fed to your dog.

Which when you think about it is a “win- win.”

Your dog gets some variety and extra nutrition and you can feel good about not sticking it straight in the trash. 

How to stop my dog from eating onions

Once you have made the decision to never add onions to your dog’s diet, the next step is to try and figure out a foolproof way to never let them get their paws on any.

How organised you need to be depends on how eager your dog is to steal food that is left on kitchen counters.

Some dogs will do it as soon as your back is turned, other dogs at least have the courtesy to wait until you have left the house.

If this is a real problem that goes way beyond onions, then you might see it as a training opportunity.

And although on the face of it that might seem like a tough ask with the right tools and attitude, you might be surprised.

How to stop your dog from stealing food from the kitchen counter

For the training you need to place a food item on the kitchen counter that your dog finds irresistible.

And you need lots of small pieces of biscuit or kibble to use as rewards.

When your dog moves towards the kitchen counter, block them and tell them “no.”

Don’t shout at them but make sure that there is a deep and serious tone to your voice.

When they start to back away, reward them with a treat and say “good boy” in a high pitched voice.

Move away from the kitchen counter again.

Basically just repeat this drill over and over until your dog can be in the kitchen without trying to steal what’s on the counter.

You have started to shift their attention. 

Instead of thinking of the food on the counter being the most important thing, they will begin to crave the reward of a biscuit instead. 

Good luck.