Just in case you don't know: iodine is necessary for normal functioning of the thyroid gland and generating its hormones. Thyroid hormones regulate the rate of metabolism in the body and play an important role in the normal growth.
Iodine is found in fish and iodized salt. In the commercial pet food, it is added as potassium iodide, sodium iodide or calcium iodide. A dog should get 1.5 mg of iodine per 1 kg of dry food. If a dog doesn't get enough iodine, it can result into a lack of the thyroid hormone (hypothyroidism). Symptoms of hypothyroidism include retardation of growth, hair loss, rapid weight gain (in older animals), weakness, changes in behavior such as irritability. Very often animals that suffer from hypothyroidism cannot have offspring.
If you suspect problems, why don't you show him to a vet? Perhaps it would help determine the best diet.
People are waiting to help.
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