This condition may be caused by an auto immune condition or tumors, among other causes. The deficient thyroid may have an effect on many organ systems, including the heart. Symptoms may include excessive hair thinning, obesity, anemia, infertility, and lethargy. Diagnosis is confirmed by a complete thyroid panel blood test. Oral doses of thyroid hormones will alleviate most symptoms and will probably need to be given for the duration of the dog’s life. Luckily, thyroid therapy is relatively inexpensive and effective.