Hypothyroidism (underactive thyroid gland) is a common endocrine disorder in dogs whereas hyperthyroidism (overactive thyroid gland) is a rare disease.
A retrospective study of dogs diagnosed with hypothyroidism found one thing that all the sufferers had in common: they were fed a raw diet. The severity of the signs with which the dogs presented varied but all recovered when the raw does was replaced with a complete, commercial, dry diet.
The dogs became ill with excess thyroid hormone because the raw diets included necks and tracheas with the thyroid gland still attached. Thyroid hormones are not destroyed by stomach acids and so are absorbed into the dog’s body.
Of course, it is possible to argue that, as long as raw food is guaranteed not to contain thyroid gland tissue, it could still be fed safely, but then there is the problem of the salmonella, e, coli, campylobacter, listeria…