The Role of Thyroid in Dogs: What Does The Thyroid Gland Do?

What function does the thyroid have in the dog’s body?

The Role of Thyroid in Dogs: What Does The Thyroid Gland Do?

A while back, we talked about sick euthyroid syndrome – a condition that complicates the diagnosis of hypothyroidism in dogs.

Say your veterinarian determines that your dog truly has hypothyroidism. What the thyroid gland does, and how does its dysfunction affects the body?.

What Does The Thyroid Gland Do?
Thyroid gland: Image Pets Adviser

What does the thyroid gland do?

The thyroid gland sits on the front of the dog’s neck–one segment on either side of the trachea (windpipe). It makes hormones – primarily thyroxine (T4), but also 3,5,3’-triiodothyronine (T3), reverse T3, and other metabolites.

T3 is the more potent hormone. The thyroid gland produces it directly as well as it can make it from T4.

These hormones consist of amino acid tyrosine bound to iodine. This is the only place the body utilizes iodine.

A negative feedback mechanism of the hypothalamic-pituitary-thyroid axis (from the brain to the thyroid) regulates thyroid hormone secretion.

In other words, a decrease in T4 triggers T4 production. Likewise, when there is an excess amount, the thyroid produces less. This ensures the correct levels of the hormone at any given time.

What do the thyroid hormones do?

Molecular level

On a molecular level, thyroid hormones

  • bind cellular receptors (intracellular DNA-binding proteins)
  • enter into cells via membrane transporter proteins
  • and interact with specific sequences of DNA to modulate gene expression.

In other words, thyroid hormones turn some genes on and other genes off.

Physiological level

On a physiological level, thyroid hormones affect many, if not, all areas of the body.

Their absence or excess may not be immediately life-threatening. However, maintaining appropriate levels is essential for a good quality of life.

Some known functions of thyroid hormones include:


The thyroid hormones help to regulate body temperature and can stimulate fat and carbohydrate metabolism.

In other words, it controls the levels of fatty acids and glucose–in the blood. Therefore, when the hormone is deficient, the blood cholesterol and triglyceride levels become elevated.

Growth and brain development

Normal growth and brain development in young animals depend on thyroid hormones. As a result, thyroid deficiency leads to growth-retardation and neurologic impairment.

Cardiovascular effects

The thyroid hormones cause an increased heart rate, cardiac output, and blood flow to many organs.

Central nervous system

Excess thyroid hormones cause agitation and anxiety, and sluggishness and dullness if deficient.

Reproductive system

Sufficient levels of thyroid hormone are necessary for fertility.

Many other effects

Further, thyroid hormones play a role in other processes such as maintaining healthy skin and good muscle tone.

Thyroid hormone importance

You can see why having appropriate amounts of thyroid hormones is critical to the well-being of dogs.

Thankfully, treating hypothyroidism in dogs is about as easy as it gets.

  • give synthetic thyroid hormone as prescribed by your veterinarian
  • follow the monitoring schedule that he or she recommends

It can take some time to find the right dose and a dog’s needs may change.

What if, despite this, your dog’s condition does not improve? Your veterinarian needs to revisit their initial diagnosis. Your dog might have the euthyroid sick syndrome.

  1. Hi, My dog has been on Thyroid pills for a couple years. He is a 13 1/2 year old Lab. In Nov. he fell over twice in one day. I couldn’t take him to the vet right away because of Covid. So after reading a lot, I thought maybe the problem was his thyroid or his thyroid medication. His main symptoms were that he had lost a lot of muscle mass in his back legs and has lost quite a bit of weight. And then he tipped over a few times. That was very scary. Since then our vet did the ACTH Stimulation test on him. He said his number was 5 before the cortisol injection and 32 after, so it looked pretty much like he has Cushings. I don’t know if his symptoms are consistent with either problem. Or I should say he has some of each. Sometimes he doesn’t eat much for days and then he’ll eat a few good meals a couple days in a row. He is still very off/balance when he walks. (I have a harness on him so I can support him at times when he seems very unsteady. He sleeps a lot. He drinks a lot of water and pees for a long time when he goes outside. He doesn’t have accidents in the house. His ribs and backbone stick out (although that might be getting better as I keep trying to get him to eat. And when he’s laying down, it does seem like he has a big belly. Overall though, I would say the main problem seems to be his weak back legs or his dizziness. Another problem that finally occured to me is his teeth are pretty bad. A few times when he seemed like when he was going to fall was when he was eating. Sometimes when he seemed like he was going to fall, he started chopping his teeth first, so I held him until he was steady. Maybe his teeth are bothering him so much that it knocks him over? I have since been softening up his food and he hasn’t tipped over since. He is 13 1/2 years old, so I don’t think he could survive surgery or a anesthesia for teeth cleaning. I have been brushing his teeth twice a day. Maybe that is helping him to be more willing to eat.

    • Hi Debbie, sorry about your baby. What you describe seems to fit Cushing’s better than hypothyroidism. Did your vet check the thyroid levels annually to make sure he’s well-managed?

      Unfortunately, there is no easy answer to this, particularly with the teeth also being bad; there is such a thing, for example, where an infection can get from the teeth in the brain.

      If he’s not eating, he could simply be weak.

      The only answer is to see a vet for a full work-up and diagnosis. There could be different things combining to an overall problem, or one thing an underlying issue for the rest. He needs a full, detailed work-up to get to the bottom of what is what.

      • Thank you so much for your reply! If he got an infection in his brain from having bad teeth, can that be reversed? I am trying. He doesn’t seem to be in pain. Thank you so much again for your suggestions!

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