The thyroid glands are in the neck of animals, there are 2, one on either side of the trachea (windpipe). They commonly cause hyperthyroidism in cats and historically we would remove them in cats, but now there is a more effective treatment option for cats with hyperthyroidism. Currently, it is more common to to do surgery on a dog with thyroid issues. The majority of dogs with thyroid issues are because of cancer. The thyroid gland can be relatively easy to remove and the hormones it produces are easily supplemented. Over all dogs do well with this procedure and is very effective if you catch it early and are able to remove the mass when it is smaller and not as invasive.