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Hypothyroidism in Dogs: Symptoms & Treatment

Nicole Cosgrove

May 21, 2021

Hypothyroidism is a common disease to dogs and can happen in any breed though there are some who are more prone who are outlined below. It is more usual for medium to large breeds of dogs to have it and spayed females and neutered males are more prone though as yet the animal medical field do not know why. It is also more common in middle aged dogs rather than the young or senior dogs, between the ages of four to ten.

There is a gland in the neck near the larynx (voice box) called the thyroid gland which makes thyroxine a hormone vital to your dog’s metabolism. Metabolism is the process where their body turns food into energy. When a dog has hypothyroidism the thyroid gland no longer makes enough thyroxine.

Dog Breeds Who are more Prone

While it can occur in any breed it is rare in miniature and toy breeds. Those that it happens in most commonly include;

Golden Retreivers


Great Danes

Cocker Spaniels

Doberman Pinschers

English Bulldogs



Labrador Retrievers

The following breeds may not be as commonly affected but they are still more at risk than others and include;


American Staffordshire Terrier




Siberian Husky

Bernese Mountain Dog


Border Collie

Chinese Shar-Pei

Symptoms to Look for in Your Dog

Usually the first sign of hypothyroidism in your dog is hair loss most often happening on the trunk, tail and back of the hind legs. Your dog’s coat will be thin and will have lost its shine, and his skin may be flaky though not itchy. If there is itchiness this may indicate a completely different health issue. Some skin patches may even be blackened. After these initial symptoms others develop including weight gain, a loss of muscle, being slow, weakness, infections in his ears and toes, slower heart rate and being cold all the time. Less common symptoms include infertility, head tilting to one side, seizures and heart problems.

What Causes The Hypothyroid to Stop Working Properly?

As we have covered, hypothyroidism in dogs happens when the thyroid glans no longer makes enough thyroxine. In the majority of cases (95%) when a dog has hypothyroidism his immune system is attacking his own thyroid and damaging it to the point where it can longer work properly. In rarer cases the lack of hormone production can be from a tumor or the thyroid shrinking. There are also some other dog diseases that can lead to him also developing hypothyroidism and in even rarer cases it may be congenital.

How Do They Diagnose your Dog?

It really does depend on what symptoms your dog is presenting but there are a few tests they can carry out. The most common one your vet is likely to perform is the Baseline T4 test. A blood sample taken from your dog is tested for levels of the T4 thyroid hormone using radioimmunoassay. Those dogs who have a gland that is not performing as it should will of course have a lower hormone level. Since there are also other health issues that can cause a low T4 number though, this is not in itself enough for the vet to give a definite diagnosis.

Another test that can be done is Equilibrium Dialysis. Basically the T4 in the blood has two forms, bound to the blood proteins and free. This test looks at the levels of free T4.

TSH level is another blood test that can be carried out. TSH stands for Thyroid Stimulating Hormone. In dogs with hypothyroidism TSH levels will be high because the body is working hard to try to stimulate the thyroid into making more of its hormone. If a vet finds that the Baseline T4 test and the Equilibrium Dialysis tests both have low results but the TSH is high, then a hypothyroidism diagnosis is probable.

A final test may be run to confirm suspicions called the TSH Response test. TSH is injected into one of your dog’s veins and after a six hour wait they then take some blood and check the T4 again. If your dog does not have hypothyroidism he will have a high T4 level. A dog that does have it will still have low T4 even after an injection.

Treating a Your Dog

There are good treatment options out there so your dog can still lead a full and happy life. It will mean a lifetime of treatment though giving medication and managing his diet carefully. The hormone he is deficient in is administered in synthetic form so that his body is able to metabolize properly once again. Dosage depends on your dog’s overall health, age and size and will be determined by your vet. Make sure you give the amount prescribed and do not try herbal remedies without first taking them over with the vet as sometimes there can be negative interactions. The most common thyroid hormone replacement drug given is L-thyroxine and is available in chewable form as well as liquid and tablet. Usually symptoms of hypothyroidism will be gone after a few months of treatment. He or she will continue to monitor your dog’s health in regular check ups and take regular blood samples.

It is super important to take the diet part of the treatment as seriously as the administering of medication. Be sure to follow the guidelines given to you. Usually the diet is reduced in fat at the start of treatment. Most dogs respond very well to the medication and diet and soon return to themselves.

If your dog has secondary hypothyroidism where it is a tumor causing the problem treatment will involve dealing with the cause as well as daily medication for the thyroid problem.

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Feature Image Credit: Mylene2401, Pixabay

Nicole Cosgrove

Nicole is the proud mom of Baby, a Burmese cat and Rosa, a New Zealand Huntaway. A Canadian expat, Nicole now lives on a lush forest property with her Kiwi husband in New Zealand. She has a strong love for all animals of all shapes and sizes (and particularly loves a good interspecies friendship) and wants to share her animal knowledge and other experts' knowledge with pet lovers across the globe.

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