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Hypothyroidism in Dogs

You notice your dog gaining weight even though their diet and exercise regimen has not changed. Puzzled, you also begin to notice that your dog is shedding excessively and acts listlessly. If these seemingly unrelated symptoms begin to affect your dog, hypothyroidism may be the culprit.

How Does the Thyroid Gland Work?

The thyroid gland is responsible for secreting hormones T3 (liothyronine) and T4 (levothyroxine) that regulate metabolism in the body. This butterfly shaped gland is essential in turning food into energy. Hypothyroidism occurs when this gland is sluggish, and does not secrete enough of these hormones.

Causes of Hypothyroidism

Many dogs develop hypothyroid because of an autoimmune disorder known as autoimmune thyroiditis. In this case, your dog’s body will work harder to produce a larger quantity of hormones. In turn, the gland will begin to lose function and symptoms of hypothyroidism arise. Dogs can also develop hypothyroidism over time and simply stop producing enough thyroid hormone. On occasion, thyroid cancer can cause hypothyroidism in dogs, but this type of cancer is typically uncommon in dogs. Some medications can cause hypothyroidism, as well.

While hypothyroidism usually affects medium to large dog breeds between the ages of 4 and 10, some breeds are more likely to develop hypothyroidism because of genetic predisposition. The breeds known to be more likely to develop hypothyroidism are:

  • Irish setters
  • Dachshunds
  • Miniature Schnauzer
  • Doberman pinschers
  • Golden retrievers
  • Labrador retrievers
  • Airedale terriers
  • Cocker Spaniels
  • Greyhounds
  • Great Danes
  • Old English Sheepdogs
  • Boxers
  • Poodles

Hypothyroidism affects male and female dogs equally, however, spayed females are more likely to develop it than intact females. German shepherds and other mixed breed dogs are less likely to develop hypothyroidism than other dogs.

Clinical Signs

If you suspect that your dog’s thyroid is deteriorating, you will witness a myriad of signs that can range in severity. The most common signs are:

  • Fur loss
  • Increased Shedding
  • Weight Gain
  • Ear Infections
  • Skin thickening and pigment darkening
  • Lethargy
  • Loss of mental energy

Other signs that are less commonly witnessed are:

  • Sterility/ infertility
  • Dilation of the esophagus
  • Decreased nerve function resulting in decreased ability to walk

Knowing the symptoms of hypothyroidism will help your vet rule out other potential causes, but hypothyroidism is not usually diagnosed by symptoms alone. The diagnosis of hypothyroidism requires your veterinarian to determine the exact cause of this disorder in your pet.


Your veterinarian will perform a series of blood tests to determine if the cause of the disorder is autoimmune thyroiditis. By testing for the presence of the T4 thyroid hormone, your veterinarian can begin to determine if your dog is suffering from hypothyroidism. If the blood tests do not offer conclusive evidence, your veterinarian may also perform an x-ray to see if there is a visible tumor affecting the gland. In addition to these tests, it is common to use urinalysis and endocrine testing to derive conclusive results. Once your veterinarian determines the cause of hypothyroidism in your dog, you can begin to look at treatment options.


Hypothyroidism is quite often very manageable once diagnosed; however, dogs with hypothyroidism will often require medication for the rest of their life. A synthetic form of the hormone levothyroxine will need to be administered daily. Levothyroxine is the generic form of the medication Soloxine. This disease also requires owners to monitor eating habits and other lifestyle elements in their dogs. Once your dog begins receiving treatment, symptoms will begin to subside.

Managing Hypothyroidism

Hypothyroidism can be managed with a proper diet and medication regimen. Many dogs require synthetic hormone treatment for their entire lives and should not have their dosages altered unless the veterinarian advises to do so. In addition, it is important to ensure that these dogs receive low fat food especially when first beginning therapy. If you are planning on introducing any supplements, remedies or other medications to your hypothyroid dog’s diet, please consult your veterinarian first to ensure that these will not interact negatively with the synthetic hormone. With proper management and care, your dog can live a full and relatively normal life with hypothyroidism.