Dr. Abdul Samad Ph.D. (Canada) Associate Dean, Bombay Veterinary College.
Hypothyroidism is a disorder of the thyroid gland. This gland has a number of functions, but is most well known for regulating your dog's metabolic rate. Hypothyroid dogs who receive proper treatment have a normal life span and are able to maintain good health well into their golden years.
While there is a genetic predisposition for thyroid disorders, environmental factors such as pollutants and allergies probably play a role as well. Hypothyroidism implies that there are lower than normal levels of thyroid hormone. This condition is most common in dogs. It is also seen in cats (very rarely) and birds (also rare).
There are several_causes that lead to a lack of enough thyroid hormone. Perhaps the most common cause of hypothyroidism is due to the development of a condition called "autoimmune thyroiditis". An autoimmune reaction is triggered for unknown reasons. This leads to inflammation and progressive deterioration of thyroid function. Genetic predisposition is another cause, as well as Environmental toxins, Malnutrition (commercial diets probably play a significant role here) and last but not least, Excessive Vaccinations.
Common Signs of Hypothyroidisim
Secondary skin diseases including allergies and skin infections
Hair loss, lack of luster to the coat, color changes to the coat
Heat seeking, lack of tolerance for the cold
Behavioral changes, including fear, aggression, apprehension