Objective: To determine the effects on serum somatotropin, 3,5,3′-triiodothyronine (T3), thyroxine (T4), free fatty acids (FFAs) and total protein levels of different feedings and age in Sakiz sheep that have a high twin-bearing rate supported by estrous synchronization. Methods: 20 newborn lambs were used in the study. Lambs were divided into 2 equal groups. The lambs in 1 group were separated from their dams following parturition, and those in other group were kept together with their dams. Separated lambs were fed commercial cow's milk for 2.5 weeks. After that, they were fed a milk substitute, hay and concentrated supplement for 2 months, and from the end of the 2 months they were fed hay and concentrated supplement. The lambs in other group were kept together with their dams only during the day and in addition were fed hay and concentrated supplement. After 2 months, they were maintained feeding only on hay and concentrated supplement. Blood samples were taken from vena jugularis of lambs at 12 and 24-48 h, and 14, 28, 42 and 56-90 days after parturition. Serum samples were analyzed for somatotropin by enzyme immunoassay, for T3 and T4 by radioimmunoassay, and for total protein and FFA by a spectrophotometric method. Results: Serum somatotropin levels were insignificantly different between the lambs with and without their dams. Serum T3 levels were generally lower in the separated lambs than those in other group. Serum T4 levels were significantly lower in the separated lambs 48 h and 90 days after parturition than those in other group. Serum FFAs were insignificantly different between 2 groups. Serum total protein concentrations were lower in the separated lambs than lambs kept together with their dams (significantly at 12 and 48 h and 14 days). Conclusion: Ingestion of colostrum and dam milk markedly affected serum total protein levels, but body weight and serum somatotropin levels were insignificantly affected. Also serum T3 and T4 levels markedly decreased with advancing age. Serum FFA levels were not affected by the trial. Copyright © 2005 S. Karger AG.