Have you ever been told that dogs shouldn't eat chocolate? Well, if you know dogs at all you'll know that they have the ability to eat any food that's in front of them...chocolate or not! So, is it worth your effort to keep all chocolate foods out of doggy reach? Or is this whole issue just one of those random urban myths that can be easily debunked with science?

Well, it turns out, it's true: dogs shouldn't eat chocolate because they can easily become poisoned by consuming this delectable treat. And it's not only dogs! Other animals — such as cats and cows — are also susceptible to "chocolate poisoning". So why is it that humans can consume large amounts of chocolate without becoming ill, while dogs become very sick -and can even die- from eating the same amount?

The answer to that question lies in the fact that compared to humans, dogs are poor at metabolizing, or breaking down, theobromine (3,7-dimethylxanthine), a chemical compound that is found in chocolate. Theobromine has a similar chemical structure to caffeine, but is present in much higher quantities in chocolate than caffeine is; it is also found in tea and cola products.

The amount of theobromine varies quite a bit depending on the type of chocolate: Milk chocolate contains approximately 1.5 milligrams of theobromine per gram of chocolate (1.5 mg/g), while dark, unsweetened (baker's) chocolate contains ten times more (15 mg/g).

For a dog, signs of toxicity can start to occur with the ingestion of 13 g of milk chocolate (or 20 mg of theobromine) per kilogram of a dog's body weight.

For example, a small dog, such as a 7 kg poodle, would only need to eat 91 g (7 kg x 13 g/kg = 91 g) of milk chocolate to show signs chocolate poisoning, whereas a larger dog, such as a 30 kg Labrador retriever, would have to consume 390 g (30 kg x 13 g/kg = 390 g). That is roughly equivalent to 2 bars of milk chocolate for the poodle, and about 8.5 bars for the retriever. Although that sounds like a lot of milk chocolate, one bar of baker's chocolate would be enough to do the retriever some harm!

Keep in mind, this is the minimum amount of chocolate required to show signs of poisoning. If a dog consumes more than the minimum amount, the effects are even worse!

But dogs don't have to be deprived from all forms of chocolate; the theobromine content of white chocolate and chocolate-flavored dog treats is minimal and therefore unlikely to cause toxicity.

So, what is it about theobromine that causes a dog to become so ill?

Normally, when chocolate is ingested, the theobromine is rapidly absorbed from the stomach and intestines into the bloodstream. It is then carried to all parts of the body and is eventually metabolized by the liver and then eliminated in the urine.

As you now know, dogs are very slow at metabolizing theobromine; it takes approximately 18 hours for a dog to eliminate one-half of the theobromine consumed from its body, whereas it only takes about 5 hours for humans. So, you can see that the levels of theobromine can therefore build up very quickly in a dog.

In its un-metabolized form, theobromine, like caffeine, acts as a stimulant. It directly affects the heart and can cause an extreme increase in heart rate, as well as irregularities in the heart rhythm. It also causes an increase in blood pressure.

The central nervous system (CNS) is also stimulated by theobromine and this leads to nervousness, restlessness, insomnia, tremors, and even seizures. Stimulation of the CNS also leads to increased respiratory rate (i.e., panting), nausea, and vomiting. Theobromine also causes a diuretic effect on the kidneys, meaning that large amounts of body water are lost by urination, which can lead to dehydration.

A dog suffering from chocolate toxicity will show signs related to stimulation of the heart and CNS. Within several hours of consuming chocolate the dog will likely be excited, agitated, or nervous; will have an increased thirst; and may vomit. Within 10-12 hours, the dog may be extremely hyperactive, have difficulty walking and coordinating its movements, and have diarrhea. If the dog is severely affected, it may develop muscle spasms, seizures, hyperthermia (dangerously high body temperature), and ultimately may fall into a coma and die.

So what do you do if you find that your dog has gotten into your stash of chocolate? You should consult with a veterinarian as quickly as possible. If the dog consumed only a small amount of milk chocolate and does not develop signs of toxicity, it may not require treatment but will be monitored closely.

Any dog that is exhibiting symptoms of toxicity or that is known to have ingested a potentially toxic amount of chocolate will be treated. Treatment typically involves the administration of emetics (to make the dog vomit), activated charcoal (to bind theobromine in the stomach and limit its absorption into the bloodstream), fluids (to prevent dehydration and to enhance excretion of theobromine and its metabolites by the kidneys), and sedatives such as valium (if required, to control tremors and seizures). The dog's heart rate and rhythm will also be monitored with an electrocardiogram (ECG), and drugs such as lidocaine may be administered to treat abnormalities in heart rate and rhythm.

Now that you know about the potentially serious effects that chocolate can have on dogs, always be sure to keep chocolate and any chocolate-containing products out of reach of your furry canine friends!

Author, Dr. Heather Hanik, grew up in northern B.C. and received her B.Sc. in biochemistry from the University of British Columbia. She went on to graduate from the Western College of Veterinary Medicine. She is currently working as a companion animal veterinarian in London, ON. In her free time, she enjoys competing in triathlons and keeping her dog, Lucy, out of trouble!

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