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Val Caron Animal Hospital

3055 Highway 69 N
Val Caron, ON P3N 1R8



Thyroid hormone ( also known as T4 ), controls an animals metabolism, and virtually every cell in the body can be affected by reduced levels of thyroid hormone. The thyroid glands , located on either side of the trachea, produce thyroid hormone. Production of thyroid hormone (T4) by the thyroid gland, is controlled by the pituitary gland. When thyroid hormone (T4) levels are low, the pituitary gland produces Thyroid Stimulating Hormone ( TSH ), which causes the thyroid gland to produce more thyroid hormone.

Common clinical signs associated with Hypothyroidism are:

*Skin and coat abnormalities ( 'Rat tail' is common )


*Weakness or lethargy

*Anemia ( reduced red blood cells in the circulatory system )

*"Tragic Face" ( thickening of the skin of the head and face )

*Slow heart rate

*Neurological signs, especially muscle weakness.

*Corneal dystrophy ( white spots on eye )

Diagnosis of Hypothyroidism

Many factors influence circulating T4, including systemic disease or illness. Thus diagnosis of hypothyroidism can be complex at times.

Usually diagnosis of Hypothyroidism is determined by a low level of thyroid hormone ( T4 ), and an elevated level of Thyroid Stimulating Hormone (TSH). This is done through bloodwork. Sometimes additional thyroid function tests are required to confirm diagnosis of hypothyroidism.

Treatment of Hypothyroidism

Fortunately hypothyroidism is readily treatable by oral supplementation with a thyroid hormone replacement called Levothyroxine. Most dogs require twice a day supplementation, because the therapeutic life of Levothyroxine is 12 hours. Treatment is for the remainder of a dogs life.

Brand names of Levothyroxine, rather than generic forms, seem to provide the most consistant and reliable treatment for dogs.

Dogs receiving excessive doses of Levothyroxine can display any number of the following signs:

*Panting, nervousness, excitability, rapid heart rate, increased thirst, and increased appetite.

Monitoring treatment of Hypothyroidism

Because each animal metabolizes Levothyroxine differently, periodic blood testing is required. Blood testing ensures your pet is receiving the proper dose of Levothyroxine ( not too much, not too little ).

Six weeks after a pet has been started on Levothyroxine, ( or 6 weeks after a change in dosage ), a blood sample is drawn, and sent to a laboratory for analysis. Timing of the blood sampling is important. Blood is drawn 4 to 6 hours after the last dose of Levothyroxine.

Once a therapeutic dose has been determined, thyroid levels should be checked yearly, unless signs of thyroid overdose exist, or significant changes in body weight occur.