Twenty Egyptian Saidi rams aging 8 months with an average body weight of about 34 Kg were used in this study. They were randomly divided into 4 groups, each one consisted of 5 animals. All animals were fed a diet consisting of commertial concentrate mixture and roughages viz; wheat straw, corn cobs, sugar cane tops and bagasse for the first (control), second, third and fourth groups respectively. The used roughages, except wheat straw, were treated with 1% urea. All animals, except the control, were fed 10g live yeast per head per day. Feed intake, weight gain, thyroid morphology and levels of thyroid hormone(T4), total cholesterol and glucose as well as T4 uptake and free thyroxine index (FTI) were investigated. The feed intake and weight gain were significantly high in groups given sugar cane tops and corn cobs as compared with the control. A significantly high T4 and glucose accompanied by low total cholesterol levels were recorded in all groups when compared to the group fed wheat straw. The present differences between the studied groups in the volume density and structure of the various components of the thyroid gland reflect the close relationship between the ration constituents and the thyroid morphology. A morphologically active thyroid gland in the groups given bagasse and sugar cane tops in comparison with the control group explains their high serum level of T4. A less morphologically active thyroid gland (compared with the control) in the group fed corn cobs, despite the relatively high T4 in the blood, may be attributed to the low thyroid hormone consumption by tissues in this group. In conclusion, this study showed that feeding uncommonly used agricultural feed residues particularly sugar cane tops and corn cobs, treated with urea and supplemented by live yeast reflects good performance of sheep which may be attributed to the slightly low iodine intake in these groups that leaded to an increase in the function of the thyroid gland in addition to the good palatability of these roughages.