If your dog has been extremely tired lately or has been having issues with their skin or hair, they could have hypothyroidism. Thankfully, thyroid problems in dogs are easy to diagnose and manage. While the exact cause of thyroid dysfunction in our canine companions isn't clear, we do know how hypothyroidism affects dogs and how to treat it.
What Is the Thyroid?
The thyroid, in dogs and in humans, is a butterfly-shaped gland located in the neck, right next to the windpipe. As part of the endocrine system, the thyroid gland makes the hormones necessary for cells to function normally. The thyroid affects the body's metabolism.
If a dog produces too much thyroid hormone, they can develop signs of hyperthyroidism, including diarrhea, increased heart rate, anxiety and hyperactivity. If the thyroid gland doesn't secrete enough thyroid hormone, you get the exact opposite — hypothyroidism, the most common thyroid problem in dogs.
Risk Factors for Hypothyroidism in Dogs
Hypothyroidism is most often diagnosed in dogs between 4 and 10 years old. In most cases, an autoimmune disorder that shrinks or inflames the thyroid tissue causes hypothyroidism in dogs. There are no known genetic causes. However, according to the American Kennel Club, medium to large breeds are at greater risk than toy and miniature breeds. The cocker spaniel, miniature schnauzer, dachshund, Doberman pinscher, golden retriever, Airedale terrier and Irish setter also appear more likely to develop the disease. While rare, dogs can also develop hypothyroidism due to cancer of the thyroid gland. Spayed and neutered dogs seem to have increased risk; however, the many benefits of spaying and neutering may outweigh this suspected risk.

Signs of Hypothyroidism in Dogs
Hypothyroidism in dogs affects every system of the body, including the gastrointestinal system, the nervous system and the circulatory system. If a dog hasn't been spayed or neutered, hypothyroidism can also affect the reproductive system.
The most common signs of low thyroid problems in dogs include:
- Excessive tiredness
- Mental dullness or depression
- Weight gain
- Skin infections
- Cold intolerance
- Skin and coat changes, such as hair loss, excessive shedding, excessive dandruff, a dry or dull coat and hyperpigmented skin.
- Excessively long heat cycles in female dogs who haven't been spayed
- Generalized weakness and other neuromuscular problems
- A stiff walk or loud breathing due to laryngeal paralysis (loss or normal function of the larynx)
How It's Diagnosed
The good news is that, unlike human thyroid problems, thyroid problems in dogs are usually easily diagnosed and managed. If you suspect your dog might be suffering from a thyroid problem, make an appointment with your pet's veterinarian. During the visit, the vet will ask you some questions, conduct an exam and will likely ask to run some lab tests — probably blood work and urine testing.
High blood cholesterol is a common indicator of hypothyroidism in dogs. Most clinics can also test for thyroid hormone levels in dogs with a simple blood test.
All this information together will build a picture for your vet so that they can determine whether or not your dog has hypothyroidism.