The thyroid is a small gland in the neck that controls how fast the body uses energy. When it does not make enough hormone, the dog slows down. This is called hypothyroidism, and it is one of the health issues the club asks breeders to watch for.
What causes it
The most common cause in dogs is autoimmune thyroiditis. The dog's own immune system slowly attacks the thyroid gland. This form is inherited, though the exact pattern is not simple [citation:1][citation:9].
Not every case is genetic. Thyroid function can also drop because of other illness, certain medications, or other environmental factors. That is why a single low test result does not always mean the dog has inherited thyroid disease.
Signs to watch for
Signs usually come on slowly, and many dogs show nothing obvious at first. Common signs include:
- Less energy, sleeping more, less interest in play.
- Weight gain without a change in food.
- A dull, dry coat, or coat loss, especially along the back and sides.
- Skin that looks thick, dry or flaky.
- Feeling the cold more than usual.
- A change in temperament.
These signs overlap with many other problems, so a vet visit and a blood test are needed before anyone can say it is the thyroid.
How it is tested
The OFA thyroid panel looks at three things: free T4 (FT4), canine TSH (cTSH), and thyroglobulin autoantibody (TgAA) [citation:8][citation:11]. TgAA is the key marker for autoimmune thyroiditis. A positive TgAA, together with the other values, tells the vet whether the dog has the inherited form.
Testing has to be done at the right time to be useful. Bitches should not be tested during or near a heat cycle. Recent vaccination can raise TgAA for weeks, so timing matters. If a result comes back unclear, the vet may suggest waiting and testing again.
Results can be registered with the OFA. Owners can choose an open or closed entry.
Treatment
Hypothyroidism is treated with a daily thyroid hormone tablet. It is not a cure, but it is usually cheap and very effective. Most dogs get their energy back and their coat improves over a few months. The dose needs to be checked from time to time with blood tests.
Breeding advice
Because autoimmune thyroiditis is inherited, a dog that tests positive should not be bred. The same goes for close relatives if the pattern is clear. Breeders are encouraged to test breeding stock before a litter is planned, not after.
According to OFA data shared by Coton breeders, about 14 percent of Cotons tested have abnormal thyroid results [citation:1]. That is high enough to take seriously.
What the club recommends in 2026
As of 2026, the club still encourages thyroid testing for breeding dogs, using an OFA-approved laboratory. If you are buying a puppy, ask whether the parents were tested and whether you can see the results. If you have questions about a test result, please write to us, call us, or come and visit us at a club event.
Sources: Yankee Coton de Tulears, OFA thyroid testing guidance, Cornell University College of Veterinary Medicine.
