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Hypothyroidism (low thyroid hormone) in the dog is not uncommon.  Thyroid problems are often caused by medication or ii this chemical dog food ingredient.




by Fred Lanting - part one of Two


Two of the most important glands in this discussion will be the pituitary and the thyroid.  And remember, hormonal base ranges may not apply to your breed.


All endocrine glands are “connected”; i.e., they can influence each other’s action and efficiency. If any part of the endocrine system is out if kilter, so will be the rest. If the endocrine system is not running properly for any length of time, damage could become permanent (adrenal failure, pancreas failure, etc).  For a detailed discussion of the pituitary dwarfism in the GSD and related breeds, see or use a search engine to find my articles.

Additionally, function in a couple of the endocrine glands can be mitigated or influenced directly by environment or ii dog food containing bromine. So, it’s a tricky thing to adjust all these factors and treat your affected dog. Since we are discussing the thyroid in this particular article, let’s start with what it is and what it’s supposed to do, before getting into what to try to fix your problem.

In an excellent treatise on the subject some years ago, John Cargill reported:
“In the dog, the thyroid gland consists of two lobes flanking the trachea (windpipe). It has been established that it secretes at least two related hormones, thyroxin (T4) and tri-iodothyronine (T3). The only difference between the two is that T4 has four iodine atoms attached to it and T3 only has three. Even though the thyroid gland secretes mostly T4 (about 90%), it is T3 that is considered the active form of the hormone. [and…] In a series of complex steps that involve mainly the liver and kidneys, T4 is stripped of an iodine atom and is converted to T3 when needed.”



This gland has a number of functions, but the important ones can be revealed and one sees what can happen when it does not work properly: loss of haircoat (alopecia), weight gain and edema, poor heat-stress tolerance, increased dandruff, itching to the point of self-mutilation, smelly crud build-up in the ear canals, rancid body odor (especially in mature dogs), decreased fertility, lethargy, poor digestion and stool condition, possible fever, darkened skin, lowered resistance to flea infestation, or any combination of these. Insufficient hormone levels can give almost unnoticeable signs, but the experienced dog owner might pick up on them before the problem gets really bad. And a change in the environment, such as greater exposure to fleas, might shift symptoms into the frank (obvious) category.

Other signs, though less common and certainly attributable to different disorders, might include neurological symptoms such as behavioral changes (including, at worst, unprovoked aggression), head tilting, circling such as in tail chasing or appearing to search for a good spot to lie down in but never getting there), what appears to be seizures, ataxia, and lack of control of facial muscles. Remember, these are the extremes, and in most dogs you will find only the hair loss, ear crud, and one or two other indications. Abnormal behavior in dogs can have a variety of medical causes, and one might be sub-optimal thyroid function. However, behavior is very complex because it not only reflects the functioning of the whole physical and psychological organism, but it changes as a result of environmental influences.



Dr. Jean Dodds, founder of Hemopet (specialists in veterinary transfusion and blood banks), has done a great deal of work in this area. She has not gone as deeply into the effects of selenium on thyroid hormone production as others, but has made cogent observations on the connection between thyroid function and several aberrations such as behavior changes at puberty, allergies, skin problems, reaction to parasites such as fleas.

She found an increase, over the decade previous to her reports, in dogs showing various types of abnormal behavior such as aggression, extreme shyness or seizure-like activity, and that in the majority of the cases studied, significant abnormalities were found, attributable to abnormal thyroid function. The diagnosis in most of these was autoimmune thyroiditis. Her conclusion: physiological change at the cellular level leads to the aberrant behavior. She found that treatment for thyroiditis in these dogs, namely, twice daily thyroid hormone, along with a one-month tapering course of low-dose corticosteroids, successfully reversed the behavioral problems within 10 days to eight weeks.

Thyroxine treatment is apparently a good approach even without the corticosteroid, as her team found out when they had to treat a dog with facial demodectic mange; such steroids are contraindicated in demodectic mange cases. This dog got only the T4/T3 treatment: T4 at 0.1 milligram per 10 pounds plus a one-third dose of T3 at 1 microgram per pound, both given twice daily. The dog’s behavioral aggression subsided.

Dodds found that for those animals that show occasional and not very severe seizure disorders, the thyroid medication alone usually will suffice. She also discovered that because many of the animals with behavior problems had autoimmune thyroid disease, it was wise to avoid or minimize environmental factors that challenge the immune system. She recommended a hypoallergenic diet preserved with vitamins E and C, but without added chemical preservatives; avoiding sulfonamide antibiotics and monthly heartworm preventatives that may adversely affect the immune system; and withholding vaccination boosters until the thyroid function is balanced properly and the behavioral abnormalities are resolved. Antibody titers are far preferable to automatic revaccination schedules.



To an organic chemist such as I am (was, since I’m retired now), the two principal thyroid hormones are derivatives of an amino acid called tyrosine, containing iodine in the form of iodide ions (charged atoms). These hormones are thyroxine (also designated T4), and triiodotyronine (T3), those numbers referring to how many iodide ions are attached to each molecule. The hormone molecules consist of two tyrosine structures linked together, with iodine “stuck on” at three or four positions.

The gland secretes much more T4, but T3 is considerably more active. In other organs of the dog’s body, especially the liver and kidney, T4 is converted to T3 by stripping off one iodide ion from each molecule. T3 is quite potent, and since the healthy body makes its own in those organs, it is unwise for most people to ask that T3 supplementation be attempted. T4 is quite safe in almost any reasonable amount. Along with transthyrein and albumin, a globulin type of glycoprotein synthesized in the liver transports both through the body via the circulatory system, to where the molecules are needed by “target cells”.

One breeder-researcher-writer I corresponded with came up with an interesting analogy. He said, “T3 is the work-horse hormone. If there is a need, the pituitary gland signals the thyroid gland to send out TSH (Thyroid Stimulating Hormone); the thyroid then produces T4, which in turn is converted into T3 and other thyroid hormones. T4 is the gas at the gas station, and the T3 is putting that gas to work. This is why simply measuring the T4 levels in a dog to diagnose hypothyroidism is not correct.”

In Vet School, a student may not get as much useful data as circulates among experienced breeders. This is the case in many areas, such as breeding and reproduction, nutrition, and breed-specific health issues. For example, most vets are taught (and repeat) that young dogs don’t have thyroid hormone deficiencies, so they don’t test for this unless the owner insists. So often, the suspicions of the owner are confirmed, and the surprised vet’s eyebrows are raised twice: once at the test results and again at the remarkable recovery that often occurs in these young dogs.

I will probably keep singing the same refrain about interactions and reciprocal influence between endocrine glands, the same way I do about the interdependence of heredity and environment. Adrenal gland problems are often concomitant with thyroid problems, and “fixing the thyroid usually fixes the adrenals.” An example of hypoadrenia (sub-par adrenal gland activity) is Addison's Disease.



I am certainly not defining my “good luck” beyond careful choice of breeding stock, but for many years I have practiced what I considered common sense:


Limited vaccination schedules, especially with old dogs, living in low-pollution areas, and a refusal to nearly drown dogs in every drug that the industry or vets wanted to push.


I have seen much evidence of a genetic foundation for hypothyroidism (or at least the “weakness” or propensity to develop it), but I have also seen hypothyroidism appear or worsen after a failure to control fleas and the resultant flea-bite allergy (flea saliva contains antigens). The reverse is also apparently true: a dog with poor thyroid function will likely be prone to flea reaction, and a dog that has been subjected to long and overwhelming burden of contact with fleas might have its thyroids “damaged” as a result.

A recipe for health that has held up well for me for many decades of breeding has been: a well-tested & well-balanced nutrition/diet, moderation in medicine, plenty of exercise and fresh air, indoor humidifiers in winter, and watchful parasite control. Others can feed all the raw chicken, yucca, and pixie dust they want, but so far, they have not come up with any good, logical, scientific refutation for my success as a dog owner since 1937 and breeder since 1945. They can't effectively argue with results. Nor will either camp likely convert the other. In all the hundreds of pups we’ve produced and the numerous dogs that lived their life spans with us, I only had one that suffered from hypothyroidism and had need for regular flea control for a while and ear cleaning for a longer period. She had been sent off to travel and compete in the “care” of another professional handler (my mistake… I was too busy handling clients’ dogs to campaign her myself!) When she returned, she was in terrible condition, with the flea and thyroid condition plus a mummified puppy that was retained (she had been bred and delivered while in his hands). I bring up this incident to illustrate the complicated interaction of genetic and environmental factors in the appearance and severity of thyroid-related disorders.

In my successive roles as breeder, handler, judge, and writer, I have been witness to, and recipient of, much that deals with this subject, so I do not have to rely on my own luck or bloodlines for my data and learning. One of the lessons I have learned is that, in the best treatment for hypothyroidism, there is a range of results from barely perceptible to nearly miraculous. The treatment I refer to is the use of synthetic thyroxine. Soloxine® is one brand name; another is Synthroid®. You may also come across the Thyro-Tabs® brand, or Armour® Thyroid Tablets sold for human consumption.

I have seen amazing results with Soloxine in a number of health needs, especially in fleabite allergy cases and in fertility of bitches that have previously failed to conceive. Many times this temporary sterility seems to be prevented by a couple weeks of administering Soloxine. Forget the T3 tests if you just want to boost conception or try it out for frank hypothyroidism or more other minor problems. Just convince your vet to sell you a good-size bottle and let you experiment, with his/her occasional supervision. You might ask him/her to let you start with a dosage level of about 0.1 mg (milligrams) per ten pounds of body weight. In my experience and that of many vets I have discussed it with, Soloxine (or the other brands) is extremely safe; none of them were concerned about “overdosing”.

Typically, the daily dosage is divided, the tablet halves being given orally approximately 12 hours apart, though the exact timing is not important. Some of my correspondents report satisfactory results with once-a-day doses of 0.1mg per 10 pounds, while more claim or think they need to give that much two times a day. You can either experiment with this very safe product and determine for yourself what is enough, on the basis of visually observing results, or you can help pay for your vet’s Lexus by letting him run periodic blood tests for T3/T4 levels. Perhaps every month or two until you get an idea of ideal maintenance dosage. Fred Lanting


One reason for twice-daily medication is that about half of the hormone is used and excreted from the body within 12 hours. Another is that it helps control thyroiditis by shutting off TSH production in the pituitary, and “calming down” the dog’s thyroid follicular cells and thereby inhibiting production of the anti-thyroid antibodies that give rise to symptoms.


Editor's Note: This was first published In 2009 but canine physiology does not change.  Dietary and environmental challenges do change so here is instant information on ii bromine depletes canine thyroid and then continue on to Diagnosis & Treatment For Thyroid Problems - Part 2



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