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Hypothyroidism in Dogs (Rare in Cats)

Hypothyroidism is the most common endocrine disease of dogs. This disease is far less common in cats, however cases do occasionally occur. This article will therefore focus on dogs, but the clinical consequences similar in cats. Hypothyroidism is most commonly seen in pets four to six years of age. Male and female dogs are equally affected, however, some vets believe that neutered dogs are more susceptible than intact dogs. The thyroid gland consists of two lobes located at the base of the neck. This gland produces thyroxine, a hormone that regulates the body’s metabolic rate, that is the rate at which it burns calories. When thyroxine is not produced in sufficient quantity a number of consequences may occur.

It is common for dogs with hypothyroidism to gain weight while only eating moderately. Not withstanding, the majority of plump and fat dogs do not have thyroid disease – they just eat too much and get too little exercise. Many owners are oblivious to weight gain in their pets, However, when an animal’s backs become flattened instead of curved and they pant heavily with every exertion, some owners bring them in for a check up. In most cases such as these, a thyroid panel is warranted.

Most cases of hypothyroidism stem from the dog’s own immune system attacking thyroid gland tissue. This condition is called autoimmune thyroiditis, or, Hashimoto’s Syndrome. Another form of hypothyroidism in dogs is idiopathic thyroid atrophy, or shrinking of thyroid gland tissue for no apparent reason. In both cases, the gland fails to produce enough of the hormone, thyroxine, and signs and treatment are the same.

Clinical Signs Of Hypothyroidism

Adequate levels of thyroid hormone are necessary for proper hair growth. When hormone levels are low, hair growth tends to be thin over the lumbar area equally on both sides. We call this bilaterally symmetrical alopecia, which is one of the hallmark signs of hypothyroidism. The back of the rear legs are also commonly affected. The pet’s hair coat is often scurfy, flaky and lack luster. The coat is commonly deficient in finer body hairs and undercoat. The tail may be bald, like the tail of a rat. An important differentiating feature of thyroid deficiency is that this hair loss is not itchy as it would be from fleas, allergic or infectious skin disease. Hypothyroid dogs commonly have excess black pigment in the skin of their groin, a condition termed acanthosis nigricans. Sometimes this pigment is also present over a large part of the body and the skin becomes flaky, oily, and thickened. Also, frayed
or broken toenails and are common.

Hypothyroidism often causes infertility is intact female dogs, as hypothyroidism commonly leads to erratic reproductive cycling. Pseudopregnancy or false pregnancy with milk flow and abdominal distension is common in these dogs.. Male dogs may also have low sperm levels, decreased libido, and subsequent infertility issues.

Some other signs of sluggish thyroid function are seen occasionally and are seen with a number of diseases that are not related to the thyroid gland. These symptoms include mental dullness or depression, cold intolerance, slow heart rate, constipation, anemia, muscle weakness and atrophy, nerve disturbances, edema, stunted growth, and slowed clotting of the blood. Hypothyroid dogs have more than their fair share of joint pain and swelling and ear and skin infections. Lethargic behavior, such as increased sleeping, less play activity and exercise intolerance may also indicate thyroid disease. It has also been reported that hypothyroid dogs have a higher incidence to KCS (dry eye).

Breeds Most Commonly Affected

Hypothyroidism seems to most commonly present in Labrador and Golden Retrievers, Dachshunds, Cocker Spaniels, Boxers, and Rottweilers.. Hypothyroidism tends to be rare in small or giant breed dogs..

Diagnosis of Hypothyroidism

Diagnosis is obtained through blood test. The serum separated from the blood sample is often creamy whitish in color due to the presence of large amounts of fats (triglycerides and cholesterol) in the blood of hypothyroid patients (a condition called lipemia). The name of the thyroid panel performed on the blood sample is TSH/T3/T4/freeT4. . Low hormone levels in the absence of signs of other diseases are diagnostic of hypothyroidism. Blood levels of T-4 are normally 1.0-4.0 micrograms/deciliter. Normal levels of T-3 are 45-150 nanograms/deciliter and normal levels of Free T-4 are 11-43 picomols/liter. T-4 hovering about one unit and T-3 and Free T-4 levels are low-normal still create suspicion of hypothyroidism if clinical signs are significant. Falsely low thyroid hormone levels can be due to administration of steroids (cortisone) or concurrent systemic disease. A TSH stimulation test can be run if the diagnosis is in doubt.


Fortunately, thyroid hormone is easily synthesized and available in inexpensive tablet form. The T4 form of the hormone is generally prescribed , l-thyroxine (levothyroxine sodium). The initial dose is 10 micrograms per pound of body weight (0.1 mg/10 lbs) twice a day. Borderline dogs are best put on thyroid hormone for a sixty-day trial. This beginning dose is in reality an estimate. All dogs need their dose individually tailored to their needs. Signs that the initial dose may be too high are agitation, excessive thirst, and diarrhea. When these occur the dose is lowered and the thyroid level resckecked. T4 is assessed 40 weeks follwing the beginning of treatment, or any time the dose has to tbe changed. Once steady state levels have been acheived, the T4 should be checked once every 6 months.


By: Roger L. Welton, DVM
Founder, Web-DVM
President, Maybeck Animal Hospital
Author Canine and Feline 101

33 thoughts on “Hypothyroidism in Dogs (Rare in Cats)

  1. Kelly Haluda says:

    My 48 lb., 7 yr. old dog has been on .5 mg. 2x/day thyroid meds for the last 2.5 yrs. Lately, I’ve noticed exercise intolerance (we walk every day for 1/2 hr. am & pm), dragging behind and panting more. I thought her meds may be too high but vet says no. She’s been on same dosage since first being diagnosed w/hypothyroidism. Do you think they thyroid problem is causing her exercise intolerance? Thanks

    • Megan says:

      It actually sounds like she may need a higher doseage. Lack of energy and tiring easily are classic signs of hypothyroidism. If she hasn’t had her levels checked in a while, she should as higher dosage is commonly required as the pet ages.

      Of course, there are several other possibilities to these symptoms as well that are completely unrelated to her thyroid condition.

    • Gwen key says:

      My Dashound has gained 3 lbs in 2 months, she’s only 6, she’s been taking meds for 3 weeks and she’s not getting better, the Dr also done complete blood work, said all internal organs look good, I’m beginning to wonder if blood work was even done, they told me all results in 15 minutes, I’m so concerned, but do not have another $200.00 to take her back.

  2. Linda says:

    My dog is panting excessively and overly agitated & to hyper ( like he had 20 cups of coffee) cannot sit down or sleep at all after the third day of this medicine. I am scared he is hyperventilating too much and having some sort of reaction? he has only had half the recommended dose. He is a 14 year old Sheltie and I am just worried if this could be to much on his heart? is this medicine dangerous to his health?

    • Benita says:

      Hi, did you find out what the panting, and the not being able to relax was contributed to? My 13 pound shi Tzu had the same symptoms that you explained, but she was not on any meds. She now has an infected ear, constantly, that always returns. Her hair is dry, and thinning. The odd day she will shudder, or react like someone has kicked her in the stomach. Thanks.

  3. Kristi says:

    My 6 yr neutered male doberman weighs 130lbs and has been on .8 dosage 2x per day. Within the past week he has started shaking, been lethargic and is unstable in his hind in. These are the same symptoms he had prior to his hypothyroid diagnosis. I increased his dosage by.8 more a day. After 4 days, there is no change in symptoms. Took him to the vet today, she checked his thyroid levels and it came back within normal range. My question…would it now be within range due to the mrdication increase, and should I continue giving the higher dose meds and wait it out to see if his symptoms improve? The vet said lower his meds back down and prescribed antiinflammatories thinking his back is causing his problems. I don’t agree, because it wouldn’t explain his lethargy and shaking (cold intolerence)

  4. April Streat says:

    Hi. I have a 5 week old puppy. He was checked by the vet 2 weeks ago, everything was ok. Then about a week ago, it looks like his fur started to thin bilaterally. Identical in location, size etc on his body. He has fur where it is thining, it just looks like someone shaved down his hair in thise apots. They occur on his front legs, on the out aide of the leg, from elbow to toes. And on his chest between his legs, and an area on his cheeks, half the size of a dime. As well as on his rump, closer to his legs. He has no signs of anything. Happy normal playful, eating, nursing, sleeping, same as the other pups, minus the fur thing. His fur seems a little thin in other areas, but just overall thin. He seems to shed when I hold him. Could something he ate make this happen? Like an allergic reaction? I cant find any info on this. Thanks! To anyone who has any idea.

  5. carolyn says:

    my 12 year old retriever shepherd mix has been on thyroid med for several years. about a year ago the hair on his back, where there were some shepherd markings and the hair was not so soft, started turning coarse. It has increased and seems to be spreading to where his hair was softer. It’s become very dry and rough. Vet thought it was from aging. anything I can do to reverse this? I use Earthborn weight control chicken based dog food.

    • Lana Logan says:

      If you find anything that helps coat plse share. My 5 years old GSD is on thyroid meds, his hair has grown but it is very rough, course and dull and further direction is a bit erratic. He was diagnosed 6 months ago. His beautiful shiny coat is no longer. Beginning to think it will be rough and course always now. Live in Zimbabwe so fancy type stuff not available

  6. Joy says:

    our 2 yo Great Dane has bilateral alopecia with darkening and gained 40 lbs in 1 year despite eating much less than our previous Dane. She has had thyroid tested now and one year ago, both came back normal. She is now only getting 2 cups of food in the a.m. and 2 in the p.m. (vet direction) and is getting into everything because she is chronically hungry. Wondering if we are missing something in her diagnosis.

  7. Connie says:

    My 12 year old sheltie has hypothyroidism his tail from his butt seems swelled could the thyroid problem cause this

  8. mahi says:

    I am really enjoying the design and layout of your post. It is very easy on the eyes which makes it all the more pleasant for me to come here and visit more often. Have you made your own theme because whoever made the theme here is so beautiful.

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