Production of severe iodine deficiency in sheep using a prepared low-iodine diet.

Extensive tests on dietary materials suitable for ingestion by sheep have led to the preparation of an appropriate diet which, when fed to the sheep, caused severe iodine deficiency. The deficiency was manifested by daily urinary excretion values which fell to levels of less than 20 micrograms iodine and by thyroxine (T4) and triiodothyronine (T3) concentrations in blood plasma which were reduced from more than 90 and 1.80 nmol/l to the low levels of less than 2.58 and 0.31 nmol/l respectively. The values were attained 5 months after feeding the low-iodine diet. Goitre was present in most of the animals and the reductions in T4 and T3 values were accompanied by increased concentrations of plasma thyroid stimulating hormone (TSH) from less than 8.6 to more than 68 ng/ml. Samples of wool removed from selected areas of the sheep showed that the iodine-deficient diet also caused a reduction in the growth of wool.