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

The Short Answer is:

In this situation, you have two options. Acting swiftly and decisively is necessary for each option. Consider doing a quick calculation to see if your dog ate enough onion to make it toxic, even if the amount of onion was only a small amount. Your dog’s weight and the amount of onion they ate are necessary for this calculation.

In this article you will know the answer to the query “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.

Acting swiftly and decisively is necessary for each option.

Consider doing a quick calculation to see if your dog ate enough onion to make it toxic even if the amount of onion was only a small amount.

Your dogs weight and the amount of onion they ate are necessary for this calculation.

The following is a more detailed explanation.

In case your head is spinning too much you can also call your veterinarian.

However a veterinarian will probably want to know the same information…

What is it about onions that makes them so problematic?

Why is onion toxic?

The chemical n-propyl disulfide in onions makes them toxic for dogs.

In large enough amounts however it can kill a dog even though the substance isnot toxic to humans (because our bodies can absorb it).

N-propyl disulfide cannot be absorbed or processed by dogs.

Therefore it attaches itself to the outside of red blood cells within a dogs body causing them to explode.

Red blood cells are the ones that carry oxygen around the body so they can not be messed with.

The more onions a dog eats however the more n-propyl disulfide is produced in their body and the more red blood cells are destroyed.

If your dog isnot treated by a vet it will become anemic and eventually starve to death.

How many onions will kill a dog?

One positive aspect of all this is that onions do not kill dogs on sight or at first sniff.

Onions need to be ingested by dogs in a certain amount and that amount varies with the size of the dog.

Larger dogs have a higher tolerance for onions than smaller dogs.

If a Chihuahua Labrador and Great Dane all ate a few slices of onion the Chihuahua would be in much greater danger than the Labrador or the Great Dane.

In addition you should be able to find out roughly what level of onion tolerance your dog has.

By this I mean the amount (by weight) of onion your dog can safely consume before going over the edge.

My use of the phrase safely eat does not mean you should add onion to your dogs diet (as you should not) I’m just pointing out that every dog has a margin of safety. 

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

I first noticed how many onions there are when I first saw this: “wow thats a lot!”

I’m thinking “wow thats frighteningly small” after having done the calculations particularly for smaller dogs.

Imagine a Chihuahua that weighs 2.5 kg (5.5 lbs).

Their body weight is 12g or 5% of their weight.

It is therefore safe for them to consume 12g of onion per day.

12g is nothing especially when it is mixed in with a delicious bit of spag bol that they have just shared with their owners. 

The French Bulldog my stepdaughter has weighs around 25 pounds or 12.5 kilograms.

Now he can consume 60 grams of onion without putting himself at risk.

However that is still a very small amount.

There are some very small onions in our cupboards right now. They are about the size of a golf ball. 

One of those onions still weighs 40 grams!

Symptoms of onion poisoning in dogs

As a result your dog ate some onions by accident.

What symptoms should you be on the lookout for?

Your dog will often look and feel sick when he is poisoned with onions.

Its your vomiting diarrhea sore stomach and general lethargy.

Over a couple of days your dogs symptoms change as his red blood cells are attacked. 

You may notice that your dog is panting a lot more than usual their gums are pale and their heart is beating very quickly- all they can do is lie on their bed staring at you.

You should contact your veterinarian as soon as you notice early signs of stomach upset.

By the time you see panting or a rapid heartbeat it could be too late. 

Two forms of onion poisoning

The answer depends on a few different factors such as how much onion your dog has consumed and how big he is.

Onions can now be poisoned in two different ways.

When they are poisoned all at once their body experiences a massive overdose.

The most common type of onion poisoning suffered by dogs is this one which is the most feared by dog owners.

Taking the Chihuahua as an example they may have eaten most of the spaghetti bolognese leftover from the night before.

The French Bulldog who ate those huge and delicious onion rings leftover from last nights steak.

During a one-off overdose the dogs body will start to absorb the compounds within twenty-four hours and the levels of poison (n-propyl disulfide) will be at their peak after approximately 72 hours (3 days).

If your dog eats an onion it may take three days to five days before any symptoms of onion poisoning appear.

However this will depend on how big your dog is and how much onion he ate as well as other factors such as his general health.

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

If the body does not take one massive hit of n-propyl disulfide this happens.

By eating a relatively large amount of onions over a few days the toxin gradually builds up in your dogs body until it starts attacking his red blood cells. 

There could be something like drip-feeding your dogs leftover cottage pie over the course of a few days…

Due to this I do not really want to comment.

Treatment of onion poisoning in dogs

You can at least be assured that your dog is in the best of hands when its at the vet. 

In order to determine what is happening to the red blood cells and oxygen levels your vet will likely conduct some blood tests.

Also they may attempt to administer activated charcoal through a tube to your dog.

By taking the toxin out of the blood charcoal should absorb the toxin. 

When you took your dog to the vet after it snacked on an onion the vet might try to induce vomiting if you were quick off the mark. 

Dog-friendly vegetables

It might be a good idea to talk about alternatives if your dog ate some onion that you fed them because you did not realize how dangerous they are.

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

Adding vegetables to your dogs diet as snacks (rather than those lifeless dog biscuits) or as part of their main meal is a good idea.

A variety of vegetables will enrich your dogs eating experience particularly in terms of taste and texture.

Furthermore they can also boost the bodys vitamin and mineral levels.

In addition to the variety they offer your dog by having so many vegetables to choose from they can also be fed raw cooked or even frozen depending on your dogs preference. 

When it comes to preparing vegetables a lot of unnecessary waste is created- think of the skins that we peel the leaves that we cut or the stalks that we throw away.

The vast majority of this is highly nutritious and can be upcycled by feeding your dog.

When you think about it it is a win-win situation.

Dogs get more variety and nutrition and you do not have to feel guilty about throwing it away. 

How to stop my dog from eating onions

Having decided not to give your dog onions the next step is to figure out a foolproof way to stop them from getting their paws on them.

You should be organized depending on how eager your dog is to steal food left on the kitchen counters.

When your back is turned some dogs will do it immediately while others wait until you have left the house before doing it.

This may be a training opportunity if this is a real issue that goes beyond onions.

Even though on the face of it that might seem like a daunting task with the right tools and attitude you might be surprised.

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

To train your dog you need to place an item on the kitchen counter that your dog finds irresistible.

It is also necessary to reward your dog with a lot of small biscuits or kibbles.

Block your dog and tell them “no” as soon as they approach the counter.

Make sure your voice is deep and serious and do not shout at them.

Reward them with a treat and say “good boy” in a high-pitched voice when they start to back away.

Move away from the kitchen counter once more.

The idea is to repeat this drill over and over until your dog can be in the kitchen without trying to steal anything from the counter.

Their attention has been diverted by you. 

Rather than thinking of the food on the counter as the most important thing they will begin to crave the reward of a biscuit. Wishing you the best.

Amanda (Author)

With over a decade of experience, Amanda is a distinguished dog trainer. Her expertise in canine behavior has transformed countless lives, fostering harmonious human-canine connections. Through compassionate and personalized approaches, she empowers owners to understand and connect with their furry companions, creating a legacy of joyful tails and transformed lives.

Osvaldo Maciel (Content Reviewer)

Osvaldo Maciel, a stalwart in the field with 14 years of experience, is a revered dog trainer. His journey is defined by a profound understanding of canine behavior, shaping unbreakable human-canine bonds. Osvaldo guides owners to connect with their beloved pets, leaving an indelible mark of happiness and transformation. His legacy shines through the countless lives he has touched.