Diagnosing and Treating Hypothyroidism in Dogs


Hypothyroidism is not limited to people; it is common in dogs as well.  This problem occurs when the thyroid gland does not produce enough thyroxine, a hormone with numerous functions such as regulating the body’s metabolic rate.

This disease is often seen in dogs that are 4 to 6 years old.  Any breed may develop this disorder, but some breeds such as Labrador retrievers, Doberman pinschers, golden retrievers, dachshunds, cocker spaniels, and greyhounds appear to be predisposed.

Since the body’s metabolic rate determines the way energy is handled, hypothryroidism often leads to progressive weight gain without an increase in food intake, explained Dr. Audrey Cook, clinical associate professor at Texas A&M College of Veterinary Medicine & Biomedical Sciences.

“Although many dogs tend to gain pounds as they age, an unexplained increase in body weight can be a sign of low functioning thyroid,” Cook said.

Thyroxine is also important for maintenance of the skin and hair coat. Often, the hair of a dog with hypothyroidism will grow slowly and may change to a lighter color. The hair may appear thin all over, particularly on the tail. Another result of the disease is flaky skin and pigmentation in the non-haired areas.

“One of the classic signs of canine hypothyroidism is the so-called “rat tail,” in which the hair is lost from the last few inches of the tail,” Cook said.

In addition to the dog’s overall appearance, hypothyroidism can affect the pet’s mental state, resulting in depression and apathy.  Other signs of the disease include sensitivity to the cold, muscle weakness, problems with nerve function, and persistent fatigue.  Problems such as chronic skin or ear infections may also be a sign of hypothyroidism.

“Owners often mistake the signs of hypothyroidism with the aging process,” Cook said. “However, these changes can be reversed with effective management. Many dogs get a new lease on life when their hypothyroidism is treated.”

Veterinarians can diagnose the disease with simple blood tests. These usually include measurement of total thyroxine levels (often called total T4), unbound hormone levels (‘free’ T4), and thyroid stimulating hormone (TSH) concentrations.

As with people, dogs with hypothyroidism can take daily oral medication to replace the missing hormone.  Once medication for this problem begins, it is continued throughout the pet’s life.  Sometimes, the dosage has to be adjusted to get the hormone levels correct.  If the thyroxine levels are too high, dogs can lose excessive amounts of weight and appear agitated.

“We do recommend periodic checks on thyroid levels to make sure the dose is on-target, but these tests are simple and inexpensive. Your veterinarian will tell you when to bring your dog in for a recheck,” Cook said.

Fortunately, once hypothyroidism is diagnosed and the dog is given the proper medication, the pet should feel better within a few weeks. It can take a little while for the hair coat to improve, but Cook said energy levels and body condition tend to improve quickly.


Pet Talk is a service of the College of Veterinary Medicine & Biomedical Sciences, Texas A&M University. Stories can be viewed on the Web at vetmed.tamu.edu/news/pet-talk. Suggestions for future topics may be directed to editor@cvm.tamu.edu.

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