Hypothyroidism in Labrador Retrievers


Labrador Retriever owners know all too well that this breed of dog has quite an appetite, but what if you notice that your Labrador has been gaining weight, and you definitely haven’t increased his food? Has he been sneaking into the kibble for a midnight Snack? And why does he seem less energetic and playful than usual, less interested in going for walks or playing fetch at the park? If you find yourself asking these questions about your Labrador, they can indicate that he might have hypothyroidism.

Hypothyroidism in Labrador Retrievers is a common medical issue, and is the most commonly diagnosed hormone condition in canines. Affecting the endocrine system, hypothyroidism can impact your Labrador’s body and quality of life in various ways. In this article, we’ll discuss how the thyroid gland works in Labradors, the symptoms of hypothyroidism, how veterinarians diagnose the condition, and how to treat it.

What Is The Thyroid Gland And What Does It Do?

Your Labrador’s thyroid gland consists of two halves, one on each side of the trachea or windpipe. The thyroid produces two types of hormones: T3 (tri-iodothyronine) and T4 (thyroxin). The only difference between T3 and T4 is that T3 is the “active” form of the hormone, while T4 is the “inactive” form.

T3 controls the body’s metabolism, including how tissues absorb fats, carbohydrates, vitamins, and minerals. The thyroid gland produces mostly T4, which the liver and kidneys convert into T3 as needed. The pituitary gland, located at the base of the brain, regulates the production of THS, or the thyroid stimulating hormone. Simply put, when levels of T4 in the body drop, the pituitary gland produces THS to create more.

What Is Hypothyroidism And What Are Its Symptoms?

Basically, hypothyroidism, or thyroid hormone deficiency, occurs when the body doesn’t produce enough of the thyroid hormone. Note that this is different than hyperthyroidism, the over-production of thyroid hormones and a condition not commonly seen in dogs.

About 95% of hypothyroidism cases in dogs are caused by one of two conditions: lymphocytic thyroiditis (inflammation of the thyroid gland) or idiopathic thyroid gland atrophy (the shrinking of the thyroid gland). In either case, the thyroid gland is eventually unable to produce sufficient levels of the thyroid hormone. Other far less common causes of the condition include failure of the pituitary gland to produce sufficient TSH (the thyroid stimulating hormone), congenital birth defects in the thyroid gland, or cancer of the thyroid gland.

Common symptoms include unexplained weight gain, lethargy, dry or lusterless coat, recurring skin, toenail, and ear infections, excessive shedding or hair loss, and intolerance to cold. Less common symptoms include seizures and infertility.

How Will My Veterinarian Diagnose Hypothyroidism in my Labrador?

In order to determine whether or not your Labrador has hypothyroidism, your vet will first perform a thorough physical exam. Diagnosing the condition can sometimes be challenging because the symptoms associated with it can also be caused by other medical conditions, so you’ll want to provide your vet with as much information as you can about the history of symptoms.

Keep in mind, for instance, that certain symptoms of hypothyroidism, such as recurring skin infections and hair loss, can also be symptomatic of other conditions like inhalant allergies, which are extremely common in Labradors. However, in hypothyroid Labradors, unlike allergic Labradors, skin will not appear red or inflamed. If hypothyroidism is a possible cause of your Labrador’s symptoms, your vet will perform a series of routine lab tests.

The biochemical profile of your dog

The biochemical profile looks at the function of internal organs and the levels of enzymes circulating in the blood. Low levels of certain enzymes like glucose, sodium, and potassium can be possible indicators of hypothyroidism.

The biochemical profile will also tell your vet if your Labrador’s blood contains high cholesterol levels, which can also point to hypothyroidism because the thyroid hormone is partially responsible for the breakdown of fats in the body. High cholesterol is seen in approximately 75% of dogs diagnosed with hypothyroidism.

Your dog’s blood count

A complete blood count, or CBC, looks at the levels of white blood cells, red blood cells, and platelets in your Labrador’s blood. A decreased red blood cell count (anemia) can indicate possible hypothyroidism because the thyroid gland is partially responsible for maintaining an optimal red blood cell level. A decreased function of the immune system can also be symptomatic of hypothyroidism, so your Labrador’s blood might show high white blood cell counts, which increase to fight infection or illness.

Your vet might also perform a urinalysis on your Labrador. Even though this test doesn’t definitively provide any indicators of hypothyroidism, it’s important to make sure that your Labrador’s illness isn’t the result of a urinary tract infection. If any of the preliminary tests show signs of hypothyroidism, your vet will perform other diagnostic tests as well.

What Specific Diagnostic Tests Will My Veterinarian Perform ON My Labrador?

One of the clearest indicators of hypothyroidism is a low level of T4 in the blood. Remember that the thyroid gland produces more T4 than T3, and a certain amount of “free” T4 circulates in the blood to be converted into T3 when the body needs it. A free T4 test, which measures the amount of available T4 in the bloodstream, can help to diagnose hypothyroidism in your Labrador.

If T4 levels are low, your vet will likely send the blood samples to a referral laboratory for further analysis, specifically to check TSH levels. Since the pituitary gland stimulates the production of T4, when T4 levels drop significantly, the pituitary gland will try to produce more TSH to stimulate T4 production, so a dog with hypothyroidism might show higher levels of TSH.

How Is Hypothyroidism Treated?

Treating hypothyroidism in your Labrador is relatively simple. Your vet can proscribe hormone replacement therapy in the form of an oral drug called Levothyroxine. Levothyroxine is a synthetic form of thyroxin (T4), which when administered will regulate the level of this hormone in your Labrador’s blood because the thyroid can’t produce enough of it. When administered, Levothyroxine will work to restore normal metabolism in the body.

How Long Will My Labrador Need to Be On Levothyroxine?

If your Labrador is hypothyroid, he will probably need to be on Levothyroxine for the remainder of his life. At first, your vet might want to check his thyroid hormone levels every few weeks to determine whether or not the dosage needs readjusting, and regular blood tests will continue to monitor levels. It will probably take several weeks for the drug to have an effect, but you should begin to see relief of symptoms and a return to normal activity and energy levels as your Labrador’s metabolism returns to normal function.

Does Levothyroxine Have Any Side Effects?

If given a correct dosage, your Labrador should tolerate Levothyroxine relatively well. As with all medications, however, some dogs can develop a rare allergic reaction. Symptoms include inflammation, vomiting, and diarrhea. Contact your vet immediately if your Labrador appears ill after taking Levothyroxine. The drug is also not recommended for dogs with hypertension (high blood pressure), heart disease, diabetes, or Addison’s disease.


Hypothyroidism (also known as thyroid hormone deficiency) is a condition in which the thyroid gland doesn’t produce enough thyroid hormone. The thyroid produces two forms of the hormone, T4 (Thyroxin) and T3 (tri-iodothyronine). T3 is the “active” form of the hormone, responsible for maintaining the body’s metabolism. T4 is the “inactive” or free form of the hormone that circulates in the bloodstream and is converted by the liver and kidneys into T3 when the body needs it.

Hypothyroidism occurs when the thyroid gland doesn’t produce enough T4, so the bloodstream doesn’t contain enough for conversion to T3. The most common symptoms are hair loss, weight gain, lethargy, a dull coat, and intolerance to cold. Hypothyroidism is a very common condition in dogs and is easily treatable with hormone replacement therapy in the form of an oral medication called Levothyroxine. Your vet will perform a series of lab tests, including a biochemical profile and a complete blood count to measure hormone levels and diagnose the condition.

The Labrador Handbook by Pippa Mattinson

If Your Labrador has hypothyroidism and your vet proscribes Levothyroxine, he’ll likely need to take it for the rest of his life and have periodic blood tests to measure thyroid hormone levels. The good news, however, is that the condition isn’t life-threatening, and as long as the correct dosage of Levothyroxine is administered regularly and according to your vet’s direction, you’ll see relief of the symptoms and your Labrador can continue to live a normal and healthy life!

Do you have a hypothyroid Labrador? How do you manage the condition? Share your thoughts!

The Labrador Site Founder

Pippa Mattinson is the best selling author of The Happy Puppy Handbook, the Labrador Handbook, Choosing The Perfect Puppy, and Total Recall.

She is also the founder of the Gundog Trust and the Dogsnet Online Training Program 

Pippa's online training courses were launched in 2019 and you can find the latest course dates on the Dogsnet website