Hypothyroidism in Dogs

Hypothyroidism refers to the insufficient production of T3 and T4 hormones from the thyroid gland, a butterfly-shaped organ located in the neck. This can lead to a decreased metabolic rate in pets – meaning they don’t burn calories as quickly.


Hypothyroidism is common in dogs but rarely seen in cats. In 95% of cases the condition arises due to damage of the thyroid gland, which can occur due to existing autoimmune diseases, general wear and tear (like “pulling” while on a tight leash), after the use of certain medications, or because of other underlying illnesses. Congenital hypothyroidism is rare.

Hypothyroidism can affect middle-aged dogs between the ages of 4-10 years in all breeds, though Golden Retrievers, Doberman Pinschers, Irish Setters, Miniature Schnauzers, Dachshunds and Cocker Spaniels are predisposed.

Hypothyroidism is not a life-threatening condition, but if left untreated it will impact your pet’s quality of life.

Clinical signs:

  • Uncharacteristic behavioral problems
  • Mental dullness and lethargy
  • Weight gain, but with no increase in appetite or food consumption
  • Exercise intolerance
  • Intolerance of cold/heat seeking
  • Skin showing dryness and hyperpigmentation
  • Hair loss (bilateral symmetrical) noticed in areas of thighs, neck, trunk and tail (rat tail appearance)
  • In severe cases, a puffy face is noticed along with thick skin folds above eyes giving rise to “tragic” facial experience
  • Slower heart rate (bradycardia)


Diagnosis and treatment:

Many diseases present similar symptoms to hypothyroidism. Some of the signs outlined above may be noticed in an otherwise healthy dog with normal thyroid function. Therefore is important that confirmative diagnosis takes place.

To do so, your vet will perform a thyroid profile test consisting of TSH (thyroid stimulating hormone) and thyroxine (T4) – both free T4 and total T4. Usually, in hypothyroid dogs, the total T4 is low, but there can be other causes for low T4, so it is important to consider TSH and free T4 when making a diagnosis. Your vet will also test for anemia and increased cholesterol levels. About 80% and of dogs with hypothyroidism suffer from hypercholesterolemia (increased cholesterol), while 50% suffer from anemia.

“Pets with various acute or chronic non-thyroid disorders may have abnormal thyroid function test results. Such disorders include acute and chronic illness, particularly fasting, starvation, protein-energy undernutrition, severe trauma, myocardial infarction, chronic kidney disease, diabetic ketoacidosis, anorexia nervosa, cirrhosis, thermal injury, and sepsis.” (From the Merck Manual).

Therefore, the diagnosis of hypothyroid is difficult to make in a dog that is sick for reasons unrelated to its thyroid function. In most pets with hypothyroidism because of non thyroid-related illness, the TSH will remain normal, and free T4 may remain normal, while in true hypothyroid dogs the TSH may be elevated and the free T4 may be decreased. The best time to run a thyroid test on a dog if you suspect hypothyroidism is when the dog has no other clinical problems unrelated to thyroid disease going on. The vet’s diagnosis can be supported with the help of imaging techniques like ultrasonography or scintigraphy (radioactive imaging) of the thyroid gland.

Unlike some other organs in the body, the thyroid cannot regenerate and you can’t replace what’s been damaged. This means the condition must be treated with synthetic medications. Thyroxine (T4) is the thyroid hormone replacement compound used for treatment in dogs. It must be given on an empty stomach, at dosages recommended by your vet and then continued for life.

The dosage is adjusted after 1 or 2 months, during which the animal’s response to treatment is gauged. Once a therapeutic regimen is stabilized, serum T4 concentrations should be checked 1-2 times per year by a licensed veterinarian.

If a dog’s symptoms do not subside – and they are being given the recommended dose of thyroid hormone – it can indicate that the dosage is incorrect or that another separate condition or disease is perhaps present. It is important to avoid increasing your dog’s thyroxine dose without consulting with your vet. If you increase the dose erroneously, you can harm your pet.

How Can Activ4Pets Help?

Activ4Pets is your dog’s digital health assistant and tracks their entire veterinary history. We collect and upload all their test results, screening, surgeries, medications and more to a secure online platform. If your pup is diagnosed with Hypothyroidism, Activ4Pets can keep all the paperwork in one place, so you always have the medical information at your fingertips to easily manage dosages and follow up. In short, Activ4Pets provides peace of mind all year round, meaning less stress while trying to remember medical details, and no more more trawling through paperwork.


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