The Link Between Hypothyroidism and Dog Aggression

Updated on April 24, 2017

Grumpy dog? Get his thyroid levels checked!


What Exactly is Hypothyroidism in Dogs?

Not many dog owners are aware of the fact that right on the dog's throat, just below the larynx, lies the thyroid gland, a butterfly-shaped gland that for the most part lives in the shadows, until it wrecks havoc on the dog's body and mind when it doesn't function as it's supposed to. This gland's primary function is to produce two hormones known as thyroxine (T4) and triiodothyronine (T3). These two hormones are responsible for controlling the dog's metabolism, regulating the heart beat, stimulating the development of red blood cells, and regulating cholesterol, along with ensuring the proper development of the dog's neurologic and skeletal systems.

In the case of hypothyroidism, the thyroid gland is under-active and fails to produce sufficient thyroid hormones. This deficiency of hormones leads to a cascading chain of events affecting many bodily functions.

What causes this insufficient production? Often, the exact cause remains unknown, but in many cases it's due to an autoimmune disorder, also known as autoimmune thyroiditis, that causes the destruction of thyroid tissue causing the thyroid gland to atrophy and work improperly. The condition can be inherited or triggered by environmental and dietary factors--think exposureto pollutants, chemicals and allergies. Affected dogs breeds include Golden retrievers, dobermans, Irish setters, dachshunds, cocker spaniels, Labrador retrievers and several others. Here is a complete list of the most affected breeds. While once it was believed that the most affected dogs were middle-aged, veterinarian W. Jean Dodds of Hemopet in Southern California has found that most diagnosed with hypothyroidism were young dogs as young as 1 year and a half, and no longer 4 or 5 as seen before.

How Hypothyroidism Affects Behavior

Many dog owners may be aware of the fact that hypothyroid dogs may develop typical hair loss affecting the sides of the body, the back of the thighs and the top of the tail. The dog's hair may fall out easily and appear to be dry and brittle. Chronic bacterial skin infections such as acral lick granulomas may be seen. Weight gain is often seen and the dog may also develop intolerance to cold, chronic constipation, anemia, deafness, low heart rate, exercise intolerance and lethargy. Not many dog owners though may be familiar with the fact that several hypothyroid dogs may also develop behavior changes, particularly evident in periods of physiological or psychological stress. Dog trainers and behavior consultants may play a key role in proper diagnosis by referring clients to their vets for medical tests anytime a dog presents with behavior changes, especially when even-tempered dogs suddenly lash out.

Interestingly, in many cases behavioral changes take place before the typical weight gain and coat changes take place, explains veterinarian Dr. Pressler in an article for the Whole Dog Journal. Common behavior changes involve the onset an attention disorders along with impaired short-term memory that may escalate into aggression, extreme shyness and even seizures with onset of aggressive behavior immediately before or after. The aggressive behavior is usually owner directed or intraspecies (directed towards dogs) according to Drs. Linda P. Aronson and W. Jean Dodds in "The Effect of Hypothyroid Function on Canine Behavior".

It's still not clearly understood how low thyroid levels may affect behavior. There are chances that lowered thyroid levels may affect the dog's hypothalamic-pituitary-adrenal (HPA) axis which controls how the dog reacts to stress. Another theory has it that the elevated levels of cortisol, sometimes found in some dogs. may cause the dog to feel in a constant state of stress. These high levels of cortisol are what ultimately may suppress the production of thyroid stimulating hormone (TSH).

How is hypotyroidism diagnosed? It requires a complete thyroid panel sent to a well-known laboratory where all the dog's thyroid hormones and autoantibodies to those hormones are tested. This involves total and free T3 and total and free T4 levels, circulating levels of thyroglobulin autoantibodies (TgAA), and T3 and T4 autoantibodies. A good place to send the blood sample is to Dr. Jean Dodds who will provide expert interpretive diagnostic comments taking into account the dog's age, sex, and breed .

*Note: The all-so-common in-office thyroid tests, such as a dog’s “total” T4 are inadequate for diagnosing hypothyroidism.

Own a dog diagnosed with hypothyroidism? Fortunately, the dog will feel much better and improve quickly after being put on L-thyroxine, also known as Soloxine given twice daily. According to a study conducted by Dr. Dodds in collaboration with Tufts University, dogs exhibiting aggression as a symptom of hypothyroidism, responded favorably within the first week of treatment, yet, it's important to continue giving the medication properly to keep the condition from resurfacing.

Disclaimer: this article is not intended to be used as a substitute for professional veterinary advice. If your dog has developed sudden behavior changes, consult with your vet to rule out potential medical problems.

Hypothyroid epidemic in dogs

Questions & Answers


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        Gabriele Hauf 7 months ago

        WOW !!! Thank you - I have had problems for years and years years - THANK YOU ... I think I have finally found the solution to the problem ...

      • alexadry profile image

        Adrienne Janet Farricelli 4 years ago from USA

        Dogs tend to get hypo, cats more likely to get hyper. Thanks for stopping by Writer Fox!

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        Writer Fox 4 years ago from the wadi near the little river

        Very interesting article. I never knew that dogs could be affected by hypothyroidism. (Maybe they are eating too much 'people food?') Voted up.