Hypothyroidism in Dogs

Is your dog losing her hair? Suddenly gaining weight? Acting lazier than usual? While it’s true that some dogs have a genetic predisposition to become hypothyroid, it can still be difficult to accurately diagnose canine hypothyroidism. Learn what causes it and recognize its symptoms to prevent misdiagnosis. Once diagnosed the common treatment for hypothyroidism is supplementation of thyroid hormone. In this article we take a close look at Hypothyroidism in dogs –causes, symptoms and treatment.

What is Canine Hypothyroidism?

Just like humans, dogs have thyroid glands located in their neck. While it has a number of functions one of the main ones is to create, and secrete, a hormone called thyroxine that controls a dog's metabolism. Hypothyroidism occurs when the thyroid decreases the amount of thyroxine it secretes into a pup's system. This lack of what is an essential hormone then goes on to affect a number of areas of the body and its functions.

Hypothyroidism should not be confused with hyperthyroidism. Hyperthyroidism is a disease in which the thyroid gland is overactive, so it is the exact opposite. While common in cats it is rarely seen in dogs.

What are the Causes and Are Certain Breeds More at Risk of Developing Hypothyroidism?

The exact cause of hyperthyroidism in an individual dog can be hard to pinpoint, but there are some common causes and factors that will be considered. As the condition usually occurs in dogs aged four to ten an age related shrinkage of the thyroid gland may be to blame or for some reason their own immune system may be attacking the thyroid.

In rare cases hypothyroidism may be caused by a tumor on the thyroid gland itself.

Studies show that the majority of dogs become hypothyroid before they reach the age of 6 years—46% are diagnosed from 1 to 3 years and 29% from 4 to 6 years.

Canine Hyperthyroidism is also a genetic-prone disease. Diane Levitan, VMD, DACVIM, from Peace Love Pets Veterinary Care writes, “Hypothyroidism is a difficult disease because it does manifest itself in several different ways. One of the most important things to understand about hypothyroid[ism] is that there is a genetic predisposition".

Any dog can develop hypothyroidism but extensive research, and anecdotal evidence seems to indicate that certain purebred dogs are more prone to developing the disease:

Just why that is is not something that experts currently fully understand and no genetic link has been discovered at this time. Studies also show hypothyroidism is more prevalent in females than in males.

Since there’s not a DNA-based test dogs can be screened from an early age using a blood test to see if they have tendency to become hypothyroid.

How Can I Tell If My Dog Has Hypothyroidism?

Whatever the cause of the disease, the symptoms, and eventual treatments, are the same. The earliest signs that you can usually observe in a dog with hypothyroidism affect the skin and coat.

The coat dulls and his skin will become flaky. He may also then begin to lose hair, usually from the back and hind quarters. These signs are sometimes mistaken for allergies, but if they are sudden onset they are good indications that your pup should visit the vet for further testing.

As the lack of thyroxine in your pup's system continues to affect him, he may lose his appetite, but despite that is likely to begin gaining weight. He may become sluggish and begin to lose muscle tone as well.

Some dogs will also develop black patches on their skin and suddenly become very intolerant to cold. Their heart rate may slow and they may become more prone to ear and toenail funguses too.

In some rare cases, hypothyroidism can lead to seizures and heart problems, but these occur in only about 5% of the cases diagnosed every year.

How Is Hypothyroidism Diagnosed in Dogs?

If you suspect that your pup may be suffering from hypothyroidism your vet will perform a series of tests to confirm whether or not that is the case. These are usually limited to a series of blood tests in addition to a full physical examination, but some vets may also choose to order imaging tests to ensure that a tumor is not present, which, as we previously mentioned, occurs in a very small number of dogs diagnosed with hypothyroidism. Blood testing is usually very accurate and in addition to confirming the diagnosis they will also give your vet vital information she will need to treat the condition properly.

How is Canine Hypothyroidism Treated?

The standard treatment for the disease is a drug based one and it is a treatment that a pup will have to follow for the remainder of their life. The most commonly prescribed drug for this treatment is one called levothyroxine or L-thyroxine and it serves to replace and replenish the supply of thyroxine in your dog's system that his own thyroid gland is no longer producing.

The precise drug dosage needed to treat a dog's hypothyroidism will be set by their vet according to a number of different factors including age, weight and any remaining natural thyroid function that your pup may have.

On an ongoing basis the drug can then be obtained from any pet pharmacy and is usually provided in tablet form. Most pet parents do find that it is easier to crush the tablet into food once their pups appetite returns, but if you decide to do that it is crucial that you make sure that they are consuming the full dose every time.


The good news for any pet parent whose furkid is diagnosed with hypothyroidism is that despite the fact that there is no 'cure' and it is a lifelong condition when it is properly managed with medication then the prognosis, and the outlook for a long, healthy live for your pup is good.

It is important that the condition be treated though, as left untreated it will seriously impact the quality of your dog's life.

Share Your Experience: Have a story about low thyroid hormone in dogs? Share it with us by leaving a comment below.

If you are concerned about your pet, visit or call your veterinarian – he/she is your best resource to ensure the health and well-being of your dog. This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet.

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