Hypothyroidism and canine aggression

Hypothyroidism is a condition that affects the thyroid gland of the dog, and when the thyroid is working as it should do without any problems, your dog should be in good health and normal temperament. However, If the thyroid gland isn’t working exactly as it should be and is not producing sufficient levels of the necessary thyroid hormones, this is known as hypothyroidism (as opposed to hyperthyroidism, where too much of the hormone compound is produced). This can in its turn go on to affect many different aspects of your dog’s health and temperament, including their propensity to aggression.

If your normally well behaved dog appears to be less tolerant than normal, rather grumpier, or even aggressive on occasions, it is worth finding out if a thyroid problem is in play. Read on to learn more about hypothyroidism, how it affects the dog, and its potential link to canine aggression.

More about hypothyroidism in the dog

In the throat of the dog just below the larynx is a gland called the thyroid, which has the main role of producing two hormones that regulate and control metabolism, as well as various other factors. Normal thyroid function is important for the dog, for as well as managing the digestive system, it also regulates the heartbeat, cholesterol levels, the production of red blood cells, and the development and maintenance of the skeletal and neurological systems.

The two hormones produced by the thyroid are called T4 (thyroxine) and T3 (triiodothyronine). If your dog is suffering from hypothyroidism, this means that the thyroid gland fails to produce enough of these two hormones, which in its turn can cause a range of problems with both the physical health and normal behaviour of your dog.

What causes hypothyroidism?

The exact cause of hypothyroidism in each dog can vary, and it may not be possible to identify in every case. In some cases, hypothyroidism is due to an autoimmune disorder, or it may be caused by external factors such as pollutants in the atmosphere, or the contents of your dog’s diet.

While all dogs of various breeds may potentially develop hypothyroidism, some breeds are rather more prone to it than others; some of the most commonly affected breeds include:

• Labrador retriever
• Golden retriever
• Doberman pinscher
• Dachshund
• Irish setter
• Cocker spaniel

Dogs of any age may potentially develop hypothyroidism, but generally the first symptoms of its onset will occur between the ages of one and five.

How does hypothyroidism affect your dog’s behaviour?

Hypothyroidism often comes accompanied by a range of physical symptoms, such as a lacklustre coat or hair loss, and a propensity to develop skin infections and irritations. Weight gain, food intolerances and a range of digestive problems also often accompany the condition, as can a general lethargy and disinterest in exercise and play.

If the condition is very pronounced or advanced, changes such as anaemia, low heart rate and a propensity to feel the cold can also be present. However, some of the most prominent and obvious effects of hypothyroidism in the dog come about in the form of changes to your dog’s normal behaviour, which can be acute and very pronounced.

In many cases of hypothyroidism, behavioural changes in the dog may occur before any physical problems become obvious, which is often confusing to dog owners who find themselves faced with some very out of character dog behaviours with no obvious cause. Short-term memory loss or an apparent inability to concentrate properly are common, as is sudden shyness or fearfulness for no obvious reason, and in some cases, seizures and aggressive behaviour towards people or other dogs present too.

Why does hypothyroidism lead to aggression?

It is important to note that canine hypothyroidism does not always lead to aggression in the dog, but this is one of the common symptoms, and an important one to be aware of. It is thought that elevated aggression levels are due to the way that the thyroid gland affects the dog’s HPI axis, which controls and modifies how dogs deal with and react to stressors.

High levels of cortisol in the bloodstream often accompany hypothyroidism too, which can lead to the dog feeling constantly stressed or anxious, and so, more likely to behave or react aggressively to normal situations.

Diagnosing and treating canine hypothyroidism

In order to diagnose hypothyroidism in the dog, your vet will need to run a panel of tests on your dog’s T3 and T4 hormone levels, which usually means taking blood samples and sending them away to a specialist laboratory for examination.

While hypothyroidism cannot be cured outright, it can be treated and managed on an ongoing basis by means of the supplemental administration of synthetic thyroid hormone medications to correct the lack of natural T3 and T4 production, and generally, dogs will begin to improve within just a week or two of treatment. After diagnosis, medication will generally be required for life, but the cost and availability of medicating for an ongoing thyroid condition are not usually prohibitive.