What Causes Low Thyroid in Dogs?

Low thyroid function is frequently seen in canines. It is due to a deficit of thyroid hormones in the dog's system. These hormones are secreted by the thyroid gland, which is also in charge of the regulation of the metabolic function. A dog with low thyroid hormones will have dry skin, coarse coat and may gain weight without eating more.

Hyperthyroid Treatment

Hyperthyroid treatment is the leading cause for low thyroid levels in canines. The hyperthyroid treatment focuses on reducing the function of the thyroid glands, and this often results in a deficit of thyroid hormones. While under treatment, the dog should be carefully monitored and the anti-thyroid medication should be discontinued if the dog has low thyroid levels.

Damaged Thyroid Glands

The dog has two thyroid glands, located at the base of the neck. The thyroid glands can be destroyed due to the presence of a tumor in the neck area. However, the thyroid glands may also be damaged by an immune system mediated disease, which causes the attack of the thyroid tissues.

Tumors in the Endocrine System

The endocrine system is made up of the pituitary gland, hypothalamus and the thyroid glands. The function of the pituitary gland or the hypothalamus will influence the function of the thyroid glands. If the pituitary gland or the hypothalamus is affected by a tumor, this may result in low thyroid hormone production.


In rare cases, the low thyroid function can be caused by obesity. The fat cells infiltrate the thyroid glands and make them less active. Obesity is easy to prevent by giving the dog a suitable diet and adjusting it according to his energy level and age.

Inherited Condition

A few dogs may inherit the condition from the parents, which may have a low thyroid function. While the condition is not life threatening, dogs that have constant low thyroid levels that are idiopathic shouldn't be bred, because the condition can be transmitted to the puppies. Certain dog breeds (mid and large sized dogs) are more prone to low thyroid.

Idiopathic Low Thyroid

The low thyroid levels can have unknown causes, so the condition is considered idiopathic. In this case, the dog will be monitored constantly to assess the activity of the thyroid glands. Regular tests will be performed to detect any possible inactive disease that may cause the low thyroid levels.

Treating Low Thyroid

The low thyroid function can be detected by performing a blood test and establishing the T3 and T4 hormone levels. Medication treatment will be administered (Soloxine) and most dogs will respond well to this treatment. The medication can be discontinued if the dog starts producing thyroid hormones at a normal rate, but the dog will need to be monitored and regular blood tests are needed, to ensure the condition does not reappear. The medication treatment should be started again if the low thyroid symptoms recur.