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The thyroid hormones T3 (triiodothyronine) & T4 (thyroxine) are produced by the thyroid glands located in the neck region. Hypothyroidism is the underproduction of the above hormones that regulate the body’s metabolism. Thyroid hormones production & release is controlled by another hormone, TSH that is released from a gland beneath the brain called the pituitary.

The disease normally occurs in middle to older aged dogs but we do see the condition in younger dogs of larger breeds.


There are 2 main causes:

  1. Idiopathic atrophy
    • here the thyroid gland cells become replaced with fat cells but there is no known biological cause for the gland not functioning properly
  1. Thyroiditis i.e. inflammation of the thyroid gland
    • inflammatory cells gradually destroy the thyroid cells
    • may be inherited in some breeds


Clinical signs include:

  • losing hair, especially on the tail, hind quarters or flank
  • dry or oily skin
  • recurrent skin/ear infections
  • increased weight & lethargy
  • unwillingness to exercise
  • seeking out of warm places

Diagnosis of the condition involves getting a blood sample to test a combination of the hormones.

If your dog is diagnosed with hypothyroidism they will need to start treatment in the form of tablets that are given once or twice daily. These tablets work by replacing the missing thyroid hormones. Unfortunately they are not a cure & therefore will need to be given for the rest of your dog’s life. You should see an improvement in your dog’s overall health in the first 2 months.

To ensure your dog is receiving the correct dose of treatment, repeat blood tests are required 4-6 weeks after starting treatment & then every 6 months.