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THYROID AND THE TERVUREN The thyroid is considered a "master gland" as it is involved in so many metabolic processes in our dogs. While it may not be obvious when things are going well, if your dog becomes hypo or low thyroid, you can see a number of clinical signs. Some of the first signs many people notice are problems with the haircoat. Hypothyroid dogs will often have a thin, brittle coat. They may lose undercoat and not replace it quickly or at all. Some dogs will even have symmetrical areas on the body that have very little hair. These dogs will have a low tolerance for cold weather unlike the normal Terv who loves to romp in the snow. Other signs can be more serious. Hypothyroidism can cause muscle weakness and nerve damage. A stiff gait, jumping problems in agility dogs, and laryngeal paralysis have all been associated with hypothyroidism. Difficulty swallowing and megaesophagus with the development of aspiration pneumonia also can be side effects of a low thyroid level. Changes in behavior including hyperactivity and aggressive behaviors may be connected to low thyroid levels. Or, lethargy and mental dullness may be noted. For a breeder, infertility is a sad side effect. Both male and female dogs are affected with bitches having short heats and males exhibiting testicular atrophy. The greatest cause of hypothyroidism is autoimmune thyroiditis, meaning your Terv’s own body attacks its thyroid gland. You may also see this called lymphocytic thyroiditis. There is also idiopathically low thyroid – meaning we don’t know why the level is low. So how can we avoid hypothyroidism and catch it early in dogs who have it before they have any serious side effects? Blood work is the key here. Some of you may remember doing TSH (thyroid stimulating hormone) response tests. You drew blood for a baseline thyroid level, then gave TSH and drew a second sample to see if the thyroid responded to stimulation. This test basically gave you the T4 (tetraiodothyronine) level of your dog. Those days are long gone. We still do blood work but newer tests have helped to refine the diagnosis. Currently a blood sample is drawn and up to eight parameters are evaluated. These include: TT4 (total thyroxine), TT3 (total tri-iodothyronine), FT4 (free thyroxine – not bound to any proteins in the blood), FT3 (free tri-iodothyronine), T4AA (autoantibodies to T4), T3AA (autoantibodies to T3), TSH (canine thyrotropin or thyroid stimulating hormone) and TgAA (thyroglobulin autoantibodies). OFA (Orthopedic Foundation for Animals) looks at three values to make their assessment of your dog. The FT4 by the dialysis method, the TSH level and the presence or absence of TgAA are the tests they use. Michigan State prefers to do the eight parameters mentioned above for their rankings and recommendations on care. The three antibody tests – TgAA, T4AA and T3AA indicate that your Terv has an immune problem with his thyroid. If your dog tests positive for TgAA, then OFA considers your dog to have autoimmune thyroiditis. High levels of TSH are also indicative of a thyroid gland in trouble. Ideally your Terv will have normal levels of FT4 by dialysis, normal levels of TSH and no TgAA. Some dogs will have a low level of free T4 by dialysis from outside influences. This could include a severe illness of some sort or medications such as glucocorticoids, phenobarbital and phenylbutazone. Sulfa type antibiotics can also lower thyroid levels as well as an iodine deficient diet. These dogs should be retested. Vaccinations have not been shown to influence thyroid levels according to MSU but estrus in a bitch may give a slightly higher than normal value. Belgian Tervurens should have thyroid levels checked yearly from about 2 to 6 years of age, then every other year or so. Obviously if you notice any clinical signs you should check right away. OFA will only issue certification on dogs over a year of age and they recommend rechecks. They currently have a list of eight laboratories approved to run the OFA thyroid panel. RANKINGS OFA Data: Belgian Tervurens #47th of all breeds listed with 292 dogs tested. Of these Tervs, 78.4% tested normal. 2.1% were diagnosed with autoimmune thyroiditis, 0.3 % had idiopathic hypothyroid function and 19.2% were listed as equivocal. Any dog that does not have normal FT4 by dialysis, normal TSH and no TgAA will be listed as thyroiditis or equivocal. Clearly Tervs have a number of clinically normal dogs with at least one blood value out of whack. Also, a dog may test normal at one or two years of age, but show thyroiditis at 5 years of age. This is why rechecks are so important. Michigan State University (MSU) data: Belgian Tervurens rank 110th of all breeds listed with 632 dogs tested. 3.0% were classified as autoimmune thyroiditis and 4.3% as equivocal. Clearly thyroid problems do exist in our breed. It is important for any breeder of Belgian Tervuren to do thyroid testing and to do periodic rechecks. If a dog tests positive for hypothyroidism, the dog can be fairly inexpensively treated with thyroid replacement. However, that does not mean that this dog should be treated and then bred. If so, we will perpetuate this problem in our breed and perhaps make it much worse. Recommended websites: www.offa.org and www.animalhealth.msu.edu/documentsFAQThryoidFunctioninDogs Deb M. Eldredge, DVM |
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