Hypothyroidism In Dogs – Symptoms & Which Dogs Are Predisposed

Common symptoms of hypothyroidism in dogs

Hair loss and poor quality hair

Hair loss is often the first symptom that is noticed in hyperthyroid dogs.

Sleeping dog on couch

The initial hair loss does not involve itching or scratching, unlike many other diseases of the skin and coat such as allergies. The loss of hair is the same on both sides of the body (bilateral and symmetrical).

Hair loss can be anywhere, but is most frequently on upper chest below the chin, down the sides of the body, with hair becoming thinner in these areas. The hair will fall out quite easily.

Often the whole coat has poor quality hair, with hair becoming brittle and having a coarse, dry appearance.

There is poor hair re-growth. This is particularly noticeable in dogs that get clipped or shaved.

In bad cases where there is exposed skin, it can look dry and scaly. There may be increased pigmentation in the skin, particularly in areas that have more friction, such as the armpit.

When there is exposed skin, it may become itchy if infections develop. In a few dogs, sores may develop.

Weight gain

Weight gain is common in hypothyroidism.

One of the roles of the thyroid hormone is regulation of metabolism. When there are low levels of thyroid hormones, the basal metabolic rate (BMR) is lower; this means that less energy is used by the body. The result is that fewer calories are needed to maintain weight. So, with the same calorie intake, a dog will start to gain weight. Often a dog will have become obese before hypothyroidism is diagnosed.

Another reason for weight gain, in some dogs, is accumulation of water and salts in the body. Some dogs on starting treatment for hypothyroidism will rapidly lose some of the weight they have gained, due to the loss of the excess water and salts.

Intolerance to cold

Depending on the time of year, a dog owner may notice that their dog seems to feel the cold more than in previous years. This again, is probably due to the lower basal metabolic rate resulting in lower energy use to keep warm.


Dogs with low levels of thyroid hormones are often mildly anemic, since there is a reduction in the number of red blood cells. Since red blood cells are the way that oxygen is carried around the body, there is less oxygen available to the organs, muscles, brain, etc.


Many dogs will start to seem to have less energy, and seem to be tired more of the time, when they develop hypothyroidism.

Lethargy is a consequence of anemia (less oxygen=less energy), and possibly the decreased basal metabolic rate.

High cholesterol

Unlike humans, dogs infrequently have high cholesterol. If cholesterol is high it is usually due to a particular disease. In many dogs that become hypothyroid, the cholesterol levels go up. Usually, if a vet finds high cholesterol in a blood panel, they will then test for hypothyroidism.

Reproductive problems

In non-spayed females, hypothyroidism can cause lack of, or irregular heat (estrus) cycles, infertility or miscarriage. In non-neutered males, there can be testicular atrophy. infertility and a lack of interest.

Other symptoms

There are a range of other symptoms that can be associated with hypothyroidism depending on the dog, the length of time that hypothyroidism has been present, and the severity of hypothyroidism. These symptoms include a slow heart beat, chronic constipation, squinting of the eyes, and other eye problems (including dry eye and uveitis), absence of heat cycles, and dilation of the esophagus (megaesophagus) which can cause regurgitation (see Regurgitation vs Vomiting, to find out what regurgitation is).

Some hypothyroid dogs will get repeated ear infections.

What ages and breeds of dogs are most affected by hypothyroidism?

A dog of any age can develop hypothyroidism. However, it is most commonly diagnosed in middle aged dogs.

Any breed, or mixed breed, can develop hypothyroidism. However, it is most common in medium and large dogs. Breeds that are particularly susceptible include English Setter, Boxer, Dalmatian, Irish Setter, Beagle and Pit Bull. A list of many breeds and the percentage of each breed found by the OFA to have hypothyroidism can be seen here.

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