Abstract
Fourty-eight lambs 5 to 14 months of age reared in Tokachi district, Hokkaido, were investigated for thyroid weight, serum thyroid hormone levels and histopathology. Goiter was detected in 9 cases, 4 diffuse hyperplastic goiters (D. H. G.) and 5 colloid goiters (C. G.), and 2 cases showed markedly increased thyroid weight. In the 4 D. H. G. cases serum thyroxine (T4) levels were lower, and triiodothyronine (T3) levels were significantly higher, resulting in significantly lower T4/T3 ratios, as compared with the normal range. On the other hand, the T4/T3 ratio was significantly higher in the 5 cases of C. G. The goiter lambs from 3 farms were fed with diets marginally low in iodine.
