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Causes of Hypothyroidism in Dogs

By Maureen Ryan. June 12, 2012 | See Comments

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Causes of Hypothyroidism in Dogs

The most common cause of hypothyroidism is an inherited autoimmune disorder called autoimmune thyroiditis. Learn more here.

Too often pet owners assume that changes in their dog’s behavior or appearance such as lethargy and loss of fur are just normal signs that a pet is getting older, but these may actually be symptoms of a problem with your dog’s thyroid gland. And, thankfully, while you can’t reverse aging, you can manage a thyroid condition.

Thyroid Problems

The thyroid gland, which sits on the throat below your dog’s larynx, produces the hormones thyroxine (T4) and triiodothyronine (T3). These control the rate of metabolism in dogs. If they have hypothyroidism, however, it means dogs are producing and secreting too little of the thyroid hormones. Without sufficient T4 and T3, a dog’s overall basal metabolic rate slows down along with other organ functions. Thus, the dog lacks energy, the skin is less able to heal itself, hair doesn’t regrow, and a host of other symptoms follow.

The most common cause of hypothyroidism is an inherited autoimmune disorder known as autoimmune thyroiditis (or lymphocytic thyroiditis), which destroys thyroid tissue. Dogs that are predisposed to thyroiditis have a normal functioning thyroid at birth but begin to have problems around early adulthood.

In some cases, hypothyroidism can be caused by a condition called idiopathic thyroid gland atrophy, which might be triggered by environmental and dietary factors. Although it’s very rare, thyroid cancer can also cause hypothyroidism in dogs.

Risk Factors

While hypothyroidism has been diagnosed in dogs of every size and breed and among mixed breeds, it is most common in medium and large breeds. Those most at risk include:

  • Golden retrievers
  • Doberman pinschers
  • Irish setters
  • English setters

Most dogs with the condition will begin to show signs around middle age (between 4 and 6 years of age). Although, giant breeds may develop symptoms earlier.

Preventing Hypothyroidism

Because the vast majority of dogs with hypothyroidism inherit it, the best way to prevent the disease is to avoid breeding dogs that test positive for the condition. To help avoid breeding dogs that are at risk for hypothyroidism, the Orthopedic Foundation for Animals (OFA) maintains a hypothyroid registry. This database identifies dogs that have been screened and found to have normal thyroid hormone levels at 12 months of age, which lowers the risk that they will pass the disease on to the next generation.  

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.

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