The thyroid glands rest on each side of the neck. These small glands secrete thyroid hormone to regulate the body’s metabolism. Hypothyroidism describes a lack of thyroid hormone production. Middle aged to older dogs as well as some breeds (e.g.: Golden Retriever and Doberman Pinscher) are most susceptible. Dogs with low thyroid hormone levels typically have a low energy level, excessive weight gain, and develop skin problems (e.g.: hair loss, dry skin, and infections). Diagnosis of hypothyroidism requires blood testing to evaluate levels of circulating thyroid hormone. Fortunately, hypothyroidism can be treated easily with lifelong oral supplementation with thyroid hormone. Prognosis is excellent for a normal life.