The Link Between Hypothyroidism and Dog Aggression

Adrienne is a certified dog trainer and former veterinarian assistant who
partners with some of the best veterinarians worldwide.

Grumpy dog? Get his thyroid levels checked!

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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. This butterfly-shaped gland mostly
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 heartbeat, 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. This 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 exposure to
pollutants, chemicals, and allergies. Affected dogs breeds include Golden
retrievers, Dobermans, Irish setters, dachshunds, cocker spaniels, Labrador
retrievers.

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 dogs diagnosed with hypothyroidism were as young as 1 year and a half,
not 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 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 of attention disorders along with impaired short-term memory that may
escalate into aggression, extreme shyness, and even seizures with the 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 hypothyroidism 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.

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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. It’s
important to continue giving the medication properly to keep the condition
from resurfacing.

Note

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

This article is accurate and true to the best of the author’s knowledge. It
is not meant to substitute for diagnosis, prognosis, treatment, prescription,
or formal and individualized advice from a veterinary medical professional.
Animals exhibiting signs and symptoms of distress should be seen by a
veterinarian immediately.

Comments

Gabriele Hauf on September 22, 2017:

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 …

Adrienne Farricelli (author) on February 07, 2014:

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

Writer Fox from the wadi near the little river on February 06, 2014:

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