The thyroid glands rest on each side of the neck. These small glands secrete thyroid hormone to regulate the body’s metabolism. An excess of this hormone increases the metabolic rate (hyperthyroidism), while a deficiency slows down the metabolic rate (hypothyroidism). Hypothyroidism is much more common in dogs; hyperthyroidism is rare and often associated with thyroid cancer. Hypothyroidism tends to develop in middle aged dogs; certain breeds are predisposed (e.g.: Golden Retrievers, Doberman Pinschers). Symptoms of hypothyroidism demonstrate a declining metabolic rate: decreased energy level, weight gain. Other symptoms involve the skin: thinning of the hair coat, dry skin, skin infections, and ear infections. Treatment of hypothyroidism is simple: lifelong oral thyroid hormone supplementation. Dogs treated with thyroid hormone replacement live normal, active lives.