Hypothyroidism in Dogs: An Educational Guide for Owners Hypothyroidism is one of the most common endocrine disorders in dogs. It occurs when the thyroid gland does not produce enough hormones to maintain a normal metabolic rate. Although any dog can be affected, it is more frequently seen in middle‑aged or older dogs and may be more common in dogs who have been spayed or neutered. In some cases, the immune system mistakenly targets the thyroid gland — a condition known as aut