Iodine deficiency may be due to inadequate dietary intake of iodine or consumption of feeds containing compounds that either interfere with iodine uptake by the thyroid gland or with normal synthesis of thyroid hormones (goitrogens). Iodine deficiency typically results in enlargement of the thyroid glands (goiter). The thyroid glands are located in the upper ventral neck on the trachea and produce thyroid hormone, important for controlling metabolism.
Goiter may be seen in animals sourced from high rainfall areas where there are iodine deficient soils, with elevated risk often following high rainfall in the autumn or winter. Goiter may also be seen in animals that have recently grazed certain white clover pastures or certain brassica crops that were high in goitrogens.
Large firm, non fluctuant, swelling of the ventral neck in an otherwise healthy animal is likely to be goiter. Differential diagnoses include bottle jaw and cheesy gland abscesses. Laboratory confirmation requires thyroid glands submitted in buffered formalin for histology.
Pelleted feeds contain supplemental iodine and should be sufficient to prevent development of symptoms associated with iodine deficiency.
Control exposure to iodine-deficient or goitrogen-rich conditions on farm, or ensure supplemental iodine is provided.