Monday, July 6, 2009

Health Testing for Thyroid Issues in Mastiffs

What is the purpose of testing for thyroid problems in our dogs? As breeders, it is essential that we identify those dogs that are phenotypically normal for our breeding programs and to gather data on the genetic disease autoimmune thyroiditis. Since autoimmune thyroiditis is considered genetic, it is important that we screen and eliminate affected dogs from our breeding programs.

Hypothyroidism is the most common endocrine disorder in dogs and almost 80% of these cases result from autoimmune thyroiditis. Although thyroid dysfuction is the most frequently recognized endocrine disorder, it is often difficult to make a definitive diagonosis.

Think of your thyroid as the" gas pedal' to your dog's body--it regulates the metabolism of all body cellular functions, thus reduced thyroid levels can manifest in a wide range of clinical signs. Since many of these clinical signs minic other causes, recognizing thyroid disease can be problematic.

Here are some common Clinical Signs of Canine Hypothyroidism:

Alterations in Cellular Metabolism
weakness / stiffness / laryngeal paralysis / facial paralysis / tragic expression / knuckling or dragging feet / muscle wasting / megaesophagus / head tilt / drooping eyelids.

Neuromuscular Problems

lethargy / mental dullness / exercise intolerance / neurologic signs polyneuropathy / seizures / weight gain / cold intolerance / mood swings hyperexcitability-- this can also include unexplained sudden aggression) / stunted growth / chronic infections.

Dermatologic Diseases
dry, scaly skin and dandruff / coarse, dull coat / bilateral symmetrical hair loss / rat tail, puppy coat / hyperpigmentation / seborrhea or greasy skin pyoderma or skin infections / myxedema / chronic offensive skin odor.

Reproductive Disorders
infertility of either sex / lack of libido / testicular atrophy / hypospermia aspermia / prolonged interestrus interval / absence of heat cycles / silent heats / pseudopregnancy / weak, dying or stillborn pups.

Cardiac Abnormalities
slow heart rate (bradycardia) / cardiac arrhythmias / cardiomyopathys/ Gastrointestinal Disorders constipation / diarrhea / vomiting.

Hematological Disorders
bleeding / bone marrow failure / low red blood cells / low white blood cells / low platelets.

Ocular (Eye) Diseases
corneal lipid deposits / corneal ulceration / uveitis Keratococonjunctivitis / sicca or dry eye / infections of eyelid glands (Meibomian gland).

Other Associated Disorders
lgA deficiency / loss of smell (dysosmia) / loss of taste / glycosuria / chronic active hepatitis / other endocrinopathies adrenal, pancreatic, parathyroid.

How do you test for thyroid problems?

Each dog tested is to examined by an attending veterinarian and have a serum sample sent to an OFA approved laboratory for testing as per theOFA guidelines. The laboratory will process the blood result and send it to OFA. OFa will then issue a certifiaction based on the lab result. Some breeders will screen their dog each year with a simple blood test and not do a new OFA certification.

I do screenings at 1 year of age, 2 years of age, before each breeding, and I submit an OFA test between 3 and 5 years of age. A dog may be "clear" at 2, 3 or even 4 years of age and then develop thyroditis at a later age. All stud dogs should have a yearly screening for as long as they stand at stud. All bitches should have a screening test done before any breeding. This is my personal practice and one I recommend to others who breed.

OFA will issue A breed database number to all dogs found to be normal at 12 months of age. Ages will be used in the certification process since the classification can change as the dog ages and the autoimmune disease progresses. OFA recommends that reexaminations occur at ages 2,3,4,6, and 8 years.

An evaluation of dogs under 12 months of age can be performed for private use of the owner, but it should be noted that few dogs are already positive at that age. For this reason, OFA will not issue a certification.

All data, whether normal or abnormal is to be submitted for purposes of completeness. There is no OFA fee for entering an abnormal evaluation of the thyroid into the data bank. Information on results determined to be positive or equivocal will not be made public (you can not find it listed on the OFA site) without explicit written permission of the owner.

What are the Thyroid Abnormalities that you test to find?

Thyroid abnormalities fall into several categories—two types will be defined by the registry. They are: Autoimmune Thyroiditis and Idiopathically Reduced Thyroid Function. Autoimme thyroiditis is known to be heritable

FYI--Sometimes a result maybe called"Equivocal"--that simply means is is neither negative or positve--it's undertermined. For those dogs with laboratory results that are questionable, therefore not definitive, it is recommended that the test the repeated in three to six months.

Autoimmune thyroiditis is the most common cause of primary hypothyroidism in dogs. The disease has variable onset, but tends to clinically manifest itself at 2 to 5 years of age. Dogs may be clinically normal for years, only to become hypothyroid at a later date. The marker for autoimmune thyroiditis, thyroglobulin autoantibody formation, usually occurs prior to the occurrence of clinical signs. Therefore, periodic retesting is recommended.

The majority of dogs that develop autoantibodies have them by 3 to 4 years of age. Development of autoantibodies to any time in the dog’s life is an indication that the dog, most likely, has the genetic form of the disease. Using today's technology only a small fraction of false positive tests occur.

As a result of the variable onset of the presence of autoantibodies, periodic testing will be necessary. Dogs that are negative at 1 year of age may become positive at 6 years of age. Dogs should be tested every year or two in order to be certain they have not developed the condition. Since the majority of affected dogs will have autoantibodies by 4 years of age, annual testing for the first 4 years is recommended. After that, testing every other year should suffice.

Unfortunately, a negative at any one time will not guarantee that the dog will not develop thyroiditis.

The registry data can be used by breeders in determining which dogs are best for their breeding program. Knowing the status of the dog and the status of the dogs lineage, breeders and genetic counselors can decide which matings are most appropriate for reducing the incidence of autoimmune thyroiditis in the offspring.

Please note that dogs should not receive any type of thyroid supplementation for 3 months prior to thyroid testing.

When I look at the results, how do I know what is "normal"?

The method for classifying the thyroid status will be accomplished using state-of-the-art assay methodology. I.E--we look at the blood result!

First, let's familiarize ourselves with the different "test" used and their indications for our use in evaluating our breeding dogs for thyroid problems.

(A.) Free T4 (FT4)—this procedure is considered to be the "gold standard" for assessment of thyroid's production and cellular availability of thyroxine. FT4 concentration is expected to be decreased in dogs with thyroid dysfunction due to autoimmune thyroiditis.

(B.) Canine thyroid simulating hormone (cTSH)—this procedure helps determine the site of the lesion in cases of hypothyroidism. In autoimmune thyroiditis the lesion is at the level of the thyroid gland and the pituitary gland functions normally. The cTSH concentration is expected to be abnormally elevated in dogs with thyroid atrophy from autoimmune thyroiditis.

(C.) Thyroglobulin Autoantibodies (TgAA)—this procedure is an indication for the presence of the autoimmune process in the dog’s thyroid.

How do the results translate into the OFA Certification?


FT4 within normal range
cTSH within normal range
TgAA is negative

Positive autoimmune thyroiditis

FT4 less than normal range
cTSH greater than normal range
TgAA is positive

Positive compensative autoimmune thyroiditis

FT4 is within normal range
cTSH is greater than or equal to normal range
TgAA is positive

Idiopathically reduced thyroid function

FT4 is less than normal range
cTSH greater than normal range
TgAA is negative

All other results are considered equivocal and will require a retesting after 6 months for a certification.

My information source for this entry is the OFA site.

Please direct any questions to me at Thank you. Catie C. Arney