Answer:
Iodine
Explanation:
Iodine is needed by animals because the body's metabolic rate is controlled by the action of an iodine hormone, called thyroxine, which is secreted by the thyroid gland in the neck.
If the animal fails to supply enough iodine through food to be able to make a normal amount of this compound, then the thyroid gland enlarges or expands trying to create enough, resulting in a common type of goiter.
