A normal thyroid gland is difficult to distinguish from the surrounding tissues. Its enlargement, referred to as goiter, is most often found in newborn kids, less often in adult animals. Feeding errors, such as incorrect iodine content in the ration or the presence of goitrogens, may contribute to its formation. The occurrence of goiter may also have a genetic basis. Mutation within the TG gene leads to abnormal synthesis of thyroglobulin – a protein essential in the synthesis and storage of thyroid hormones. In Poland, the most common problem is congenital goitre, with a genetic background, caused by an increase in inbreeding in the herd.