A little about the thyroid. This small gland is a hormone producer that affects many parts of the body. T3 is usable thyroid hormone, while T4 must first pass through the liver and other tissues before it can become T3, the usable thyroid. The thyroid gland itself is regulated by two different hormones. Hypothyroidism, the shortage of usable thyroid in the body is usually the condition seen when a thyroid imbalance is suspected.
Hyperthyroidism is uncommon in dogs.
We'll name a few here, as space permits. In order for dogs to have healthy skin and coats, the cells that make up the body must be healthy and multiply. It is not fully understood, but the thyroid gland is essential in regulating the metabolism of each individual cell. Whenever cells cannot function efficiently, once of the visible results is the skin will loose it's elasticity, and can ultimately result in dry, crusty, scaly skin. The end result is a dog with a sparse coat, and a dull hardened gray skin that will have an obnoxious odor.