Hyperplastic thyroid glands (goiter) occasionally occur in swine. Goiter usually occurs as a result of one of the following: iodine deficiency in the pregnant sow; a genetic defect in the sow for the biosynthesis of thyroid hormones; ingestion by the gestating sow of goitrogenic substances (certain plants, drugs, or chemicals); or iodine toxicity from dams being fed an excess of iodine.
In swine, goiter usually occurs in iodine deficient regions where iodized salt has not been included in the dam’s feed. Deficiency of iodine leads to the birth of weak or dead pigs that are largely devoid of hair. Many of the pigs have a mucinous edema, especially over enlarged foreparts of the body. The skin in these areas is thick and doughy. The tongue is often edematous and may protrude from the oral cavity. Enlarged thyroid glands (goiter) in piglets may not be visible externally but often can be palpated or observed at necropsy. In mature swine, iodine deficiency is not usually a significant disease although gestation may be prolonged by as much as seven days. Iodine deficiency is easily avoided by using iodized salt in the ration of gestating sows.