Introduction. The dynamics of the functional activity of the thyroid gland in cows kept in the iodine-deficient territory of the Republic of Tatarstan has been studied. Iodine deficiency leads to various diseases of animals, to a deterioration in the quality of livestock products, causing significant damage to livestock. In the form of monomicroelementoses, these diseases in cows occur rarely and often with a hidden clinic, which makes it difficult to diagnose and develop preventive measures in a timely manner. Most often, various polymicroelementoses are registered in animals, which are characterized by an imbalance in the content of several trace elements. Materials and methods. To determine the thyroid status of cows, we conducted clinical and laboratory studies in a number of farms in the Arsky district of the Republic of Tatarstan. The study of the dynamics of the content of iodine, thyroid hormones and thyrotropin in the blood was carried out in 25 clinically healthy cows of Holstein black-and-white breed. Research results. When determining protein-bound iodine in the blood of cows during the stall period, a decrease in this indicator was found in winter with an increase in concentration by May. Fluctuations in the concentration of iodine in the blood of cows affect the functional activity of the thyroid gland. The lowest concentration of thyroid hormones is observed in the month of April with a correlative increase in thyroid-stimulating hormone. A decrease in the functional activity of the thyroid gland occurs due to a more active form of thyroid hormones − triiodothyronine. A decrease in the activity of the thyroid gland coincides with cases of congenital goiter in calves.