The thyroid gland, located near the base of the neck, is responsible for producing thyroxine, a hormone that regulates the metabolic activities of animals. Hypothyroidism is a disease that is caused by lower or insufficient production of the thyroid hormone. It is a common health problem that equally affects both male and female dogs.

Deficiency of Thyroid Hormones in Dogs

Causes
It is usually caused by the impairment of the thyroid gland, when it fails to produce and release adequate amount of hormones required to carry out metabolic activities. Sometimes, the damage of this gland is done by the dog's own immune system and this condition is known as autoimmune thyroiditis. In this condition, the cells of the thyroid gland are destroyed by the immune system. At other times, it is caused by atrophy of the thyroid tissues and the consequent invasion of these tissues by fats.

The production of thyroid hormone also depends on other glands like the pituitary and the hypothalamus and therefore, problems in these parts of the body may also result in hypothyroidism. But, in most of the cases, it is a result of the inability of the thyroid gland to produce the required amount of hormones.

Symptoms
There is no specific symptom of this condition and the dogs suffering from the disease may show several symptoms. The dogs show symptoms like hair loss, obesity, anemia, skin problems such as hyper-pigmentation, especially black pigmentation in the skin near the groin, lethargy or reduction in mental alertness, slow heart rate and high level of blood cholesterol. Besides, an increase in sensitivity to cold, edema and toenail and skin infections are also commonly found in dogs with this disease.

Diagnosis and Treatment
It is commonly diagnosed by carrying out blood tests to determine the levels of T4 and T3 thyroid hormones. Initially, the blood is tested for checking the level of T4 hormone. A low count of this hormone usually indicates malfunctioning of the thyroid. But this is not a definitive test, as sometimes lower levels of the T4 hormone may be induced by factors other than hypothyroidism. If the level of this hormone is low, then another blood test is carried out to determine the level of T3 hormone. However, in its early stage, it may not be an accurate test for diagnosing the disease.

The confirming test for this condition is the TSH(thyroid stimulating hormone) test, which is performed if the blood tests confirm low levels of T4 and T3 hormones. In the TSH simulation test, a small dose of thyroid stimulating hormone is administered into the vein of the dog and after few hours the blood is tested for the T4 hormone. If the dog is suffering from hypothyroidism, then there won't be any change in the level of T4 hormone. However, if the level of this hormone increases in blood then it indicates that factors other than hypothyroidism may be responsible for causing a low level of T4 hormone in the bloodstream.

Thyroidism can be easily treated by administering the hormone thyroxine, which maintains the normal rate of metabolism. However, the treatment has to be continued lifelong. Besides, it is also crucial to administer this hormone in the appropriate amount. Therefore, it is important to take the advice of a certified veterinarian.

It has been observed that middle-aged dogs are commonly affected by this disease. Moreover, it is also common among mid to large breeds, while quite rare in small breeds of dogs. Breeds like Labrador, Golden Retrievers, Doberman Pinschers, Dachshunds, Cocker Spaniels, Airedales and greyhounds are found to be more prone to hypothyroidism. So, if your dog is showing symptoms like sudden obesity, hair loss, skin disorders, laziness and reduced mental alertness, a veterinarian should be immediately consulted for early detection and treatment of the disease.