Symptoms of thyroid problems in dogs include vomiting and diarrhea, increased appetite, weight loss, breathing problems and a rapid heart rate, states petMD. If the thyroid gland underproduces certain hormones, the symptoms include lethargy, hair loss, weight gain, skin infections and weakness.
Thyroid problems in dogs are either hyperthyroidism or hypothyroidism, explains petMD. In hyperthyroidism, the thyroid gland overproduces hormones, while the opposite is true in hypothyroidism. Overproduction causes a dog to become hyperactive, resulting in increased appetite and thirst and weight loss. This hyperactivity also results in an increased or abnormal heart rate or heart murmur. The thyroid gland enlarges to account for the increased hormone production, which can appear as a lump on the neck. Either the thyroid gland is removed to treat this problem or medications are given to keep the gland from overproducing.
The thyroid gland underproduces in hypothyroidism, depriving the body of hormones that help the metabolism function and the dog stay active, according to petMD. The metabolism slows, and the dog experiences lethargy, energy loss and weight gain. Severe cases of hypothyroidism can result in seizures and infertility. This condition can be treated with medication and oral doses of hormones. Sometimes dietary restrictions need to be imposed on the animal.