Canine Hypothyroidism

The thyroid gland is a small gland that works in conjunction with the pituitary gland that controls hormones called thyroxine and triiodothyronine, commonly known as T4 and T3 respectively. Just like with people, dogs and cats can have issues with their thyroid gland. Typically, when a dog has issues with their thyroid gland, it is hypothyroidism. Basically, this is just a fancy medical term that means the body produces less than the normal amount of the thyroid hormones. This blog is going to discuss hypothyroidism in dogs.


There are two common reasons that a dog develops hypothyroidism, lymphocytic thyroiditis and idiopathic atrophy. Lymphocytic thyroiditis is a genetic autoimmune disease. Idiopathic atrophy basically means the cause is unknown. Most dogs start showing clinical signs of hypothyroidism before the age of 6 years old – with a majority between the ages of 1-3 years old. Like most autoimmune endocrine diseases, hypothyroidism is more common in females than males.


As previously stated, some hypothyroidism is due to genetics and there are certain breeds that are predisposed to it. Golden Retrievers, Doberman Pinschers, Dachshunds, Shetland Sheepdogs, Irish Setters, Airedales and Cocker Spaniels make up that list of breeds with a higher risk of thyroid issues.


Since the symptoms of hypothyroidism can be similar to other conditions, if you notice any of the following issues, it is best to have a veterinarian examine your dog:

  • Loss of hair – often around the flank (abdomen), hind quarters and tail
  • Dry, scaly or thickened skin
  • Dull, brittle hair
  • Hair coat thinning or patches of alopecia
  • Bleaching of the hair coat
  • Development of oily skin
  • Lethargy (less active)
  • Being overweight or significant weight gain, even though they have a controlled diet
  • Being uninterested in favorite activities
  • Intolerant of cold
  • Slower heart rates
  • Females that give birth tend to have decreased vitality and lower birth weights with their pups


Once your veterinarian does a physical exam, they will recommend bloodwork to review the level of thyroid hormones in the dog’s body. Typically, the veterinarian will be reviewing the dog’s T4 levels. But there are many things that can cause a lower T4 result including:

  • The time of day the blood was drawn. Dogs and cats T4 levels fluctuate every 20-30 minutes.
  • The age of the dog.
  • Dogs on NSAIDs like carprofen (Rimadyl) will lower the T4 levels in the dogs blood.
  • The breed of the dog. Not only are there certain breeds that are more prone to hypothyroidism but sight hounds like the greyhound actually have a lower T4 level than other dog groups.

If your dog has a lower T4 but falls into one of the above categories, there is a T3 test that can give a more precise answer as to how your dog’s thyroid gland is working. The T3 test tends to be more expensive.


If your dog does have a lower T4 or T3, they will have to be supplemented with a canine thyroid medication. Usually this medication is given orally twice a day. You can start to see improvement with your dog’s overall health in 2-4 weeks but can take up to 6 months to see any changes in your pet’s coat. After your dog has been on the thyroid medication for a month or two, they will need to come back to the veterinarian to have their T4/T3 level rechecked. This will allow the vet to see if the supplement is working the way it is supposed to. Sometimes, the dosage will need to be adjusted to fall back into the normal range. This process may take 2 or 3 more times to find the optimal dose for your individual pet.  Thyroid medication is a lifelong therapy and the dog will need to have annual exams and bloodwork to make sure the medication is still working properly.


With the proper thyroid supplement, your dog can live a happy, long life.


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