Hypothyroidism in Dogs

  • By: Mick Whitefield
  • Time to read: 6 min.

Hypothyroidism in dogs occurs when the animal cannot secrete enough thyroid hormones and is usually caused by a thyroid disease. Thyroid disease is relatively common in some breeds of dog and for those affected it can cause your pet’s metabolism to slow down.

Just to be certain of what we here are talking about in this article from Top Lap Dogs please digest this first – The THYROID GLAND regulates the bodies metabolic rate.

As such :-
HYPOTHYROIDISM is when the bodies metabolic rate slows down due to an UNDERACTIVE thyroid.
HYPERTHYROIDISM is when the body overproduces the thyroid hormone, increasing the metabolic rate, due to an OVERACTIVE thyroid.

Hypothyroidism in Dogs

While hypothyroidism is usually a treatable condition, learning that your four-legged buddy has it, is understandably concerning. However, the condition usually responds well to correct medication.

Thyroid Glands In Dog
Thyroid Glands are located in the neck

Located in the dog’s neck, the thyroid gland produces the hormone thyroxine (T4) and several other essential thyroid hormones. These play an important role in the dog’s metabolism and, when not generated at normal levels, can cause major problems.

In a way you could say that the thyroid is comparable to a body’s thermostat operating the flow of hormones, opening and closing the flow as needed, hypo or hyper, dependant upon the bodies needs and simply becomes problematic when the thermostat works incorrectly.

Signs and symptoms of Hypothyroidism

There are a number of early indicators such as:

  • A gradual gaining of weight.
  • Behavioural changes such as unusual aggression.
  • A lack of general interest in what’s occurring in the household.

The Bigger Problems To Take Notice of are:

  • Lethargy (constantly lying down).
  • Appearing depressed.
  • Dull looking hair and hair loss (patches of hair falling out).
  • Constantly curling up next to the radiator (feeling cold).
  • Constant Skin Infections and Skin flaking or scaling.
  • A lack of fluid mobility (due to stiff joints).
  • Continual Diarrhoea.
  • A variety of eye problems.
  • Breathless when walking.
  • Heart beat issues (irregular).

If any of the above have appeared and continue to reoccur take your pet to the vet.

Common signs as mentioned above include dull coat, fur loss/thinning, excess shedding, skin scaling, adding weight due to reduced physical activity, and reduced cold tolerance. 

The primary hair loss occurs over the animal’s body, sparing the legs and head, and is not usually accompanied by any redness of the skin or itching, it just appears as though your dog is going bald. Specific areas affected by hair loss include the dog’s trunk, tail, and back of the rear legs.

Hypothyroid Dog Fat With Hair Loss
Bulldog looking typically overweight from Hypothyroidism and showing signs of hair loss

Their coat will be thin and dull, the skin flaky (a bit like dandruff), and skin colour dependant they may also have black patches. Some dogs might have increased skin pigmentation and thickening of the skin, especially in those body areas of friction, such as the axilla (armpit).

Signs that are less commonly recognized but seen in a small number of dogs can include megaoesophagus (dilation of the oesophagus). This can cause regurgitation of food or bile and abnormal muscle or nerve functions may lead to abnormal or weakness which may appear as a strange gait when walking.

Although hypothyroidism affects all breeds, the condition is usually seen in middle-aged large to medium breeds aged between 4 and 10. It’s often found in Labrador Retrievers, Golden Retrievers, Doberman Pinschers, Dachshunds, Boxers, Irish Setters, and Cocker Spaniels. It is less frequently seen in small and tiny breeds.

Causes of Hypothyroidism in Dogs

Either of these two diseases causes hypothyroidism in dogs:

  • Lymphocytic thyroiditis
  • Idiopathic thyroid gland atrophy. 

Whilst there are some genetic causes these two causes account for over 95% of hypothyroidism cases. The other 5% may be genetic or due to rare diseases such as thyroid gland cancer.

Lymphocytic thyroiditis is the most common cause of hypothyroidism in dogs and is deemed an immune-mediated disease. 

  • The animal’s immune system mistakenly assumes that the thyroid gland is a dangerous invader and begins attacking it. No matter the cause of hyperthyroidism, the symptoms and the treatment approaches are the same.

Monitoring your dog’s condition is important because most of the time, the symptoms of lymphocytic thyroiditis go unnoticed until hypothyroidism appears. If you think the dog shows any of the signs highlighted above then contact your veterinarian and discuss your concerns listing those factors you have noticed. 

Diagnosing Hypothyroidism

Hypothyroidism in dogs left untreated, impacts the basic quality of life for your dog. It’s, therefore, important to consult with your vet if you think your dog has the condition so that you can get a professional diagnosis.

Vet Examining Dogs Neck
Thyroid Glands Hyperthyroidism

A hypothyroidism diagnosis is most typical in dogs between ages 4 and 9 years. Both females and males can get the disease.

The most commonly used test is a total thyroxin (TT4) level screen test. This measures the main thyroid hormone in an animal’s blood sample.  A low-level count together with the verified clinical signs is suggestive of Thyroid disease.

Definitive diagnosis is usually made through a ‘free T4 by equilibrium dialysis’ (also known as ‘free T4 by ED’ or a thyroid panel. The test is used in assessing the levels of multiple types of thyroxin. 

If the free T4 by ED test is low, it may mean your dog has hypothyroidism. However, note that some dogs can show a low TT4 (total thyroxin) and they may have a normal free T4 by ED level. Such animals don’t have hypothyroidism.

If this is the case, then depending on the condition of your pet, additional tests may be necessary. 

Treatment of Hypothyroidism in Dogs

Hypothyroidism often leads to hair coat changes and a lustreless, dull lookingh coat of hair. Skin changes may include scaling, hyperpigmentation, and recurrent infections. The diagnosis of hypothyroidism should never be made solely on low T4 concentration. To make a conclusive diagnosis, multiple hormone tests may also be needed.

The good news, however, is that hypothyroidism is not life-threatening. And, it’s generally inexpensive and fairly easy to treat. Although it has no cure, the treatment is straightforward, and the prognosis good when appropriate doses of levothyroxine are administered. Levothyroxine is a synthetic T4

The dosage will vary depending upon the dog’s thyroid levels and the dog’s weight. As treatment progresses, your vet may need to adjust the dosage as tolerance levels change. You can expect to see some changes in your dog after one to two months of drug therapy. 

Once your vet has determined a stable dose, you will most likely need to have your dog’s thyroid levels retested at least once a year or twice a year. Because the condition has no cure, your pet has to continue using the thyroid replacement hormone for the rest of his life. 

Caring for a Dog with Hypothyroidism

The best way to manage hypothyroidism in dogs is with medication from the vet. There are no proven home or natural remedies for the disease. Left untreated, your dog will continue feeling poorly, and the symptoms will simply get worse. Eventually, your dog may experience severe complications, which may prove to be fatal.

With successful drug therapy, your pet’s outlook is excellent, and as long as they remain on any treatment program, the animal can live a happy, long life without any severe symptoms. 

Your dog will still need regular checks at the clinic, but these can most likely be fitted in with any annual check-up. If your dog shows any other signs then the vet may need to perform repeated blood tests to ensure the thyroid hormones are at the right level, and that the dog has not developed a thyroid replacement hormone intolerance.


This is not just a case of having a fast dog, it is a serious condition that needs medical help.

Fat Dog
Not just fat

The thyroid gland is responsible for regulating the animal’s metabolic rate. If it’s overactive (case of hyperthyroidism), the metabolism is elevated. The metabolism slows down if the thyroid is underactive (hypothyroidism).

Unfortunately, because the thyroid gland cannot regenerate or repair itself, hypothyroidism is a lifelong disease. It’s also important to point out that hypothyroidism is also genetic, and, therefore, breeding dogs with the condition isn’t recommended.

Although hypothyroidism has been reported in older and younger dogs, it normally affects middle-aged dogs. The condition can affect any breed, although some specific breeds like Labrador Retrievers and Doberman Pinschers are more prone. 

This disease is treatable with medication which is relatively cheap, ignoring the signs may ultimately cause severe problems.

Non Shedding Hairy Dog

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