Effect of manganese on thyroid function in sheep

Ten healthy adult male sheep aged about 1 year old were randomly allocated into two equal groups of control (no treatment group, n = 5) and experiment (n = 5). The two groups were kept under the same conditions of food and environment. Sheep of experimental group received MnSO₄, H₂O (5 mg/kg/day, SC) from day 0 for 8 weeks. Blood sampling of the two groups were done on days 0, 14, 28, 42, 56, and 70 at 11 a.m. Serum T4, T3, FT3, FT4, TSH, manganese, creatinine, and blood urea nitrogen concentrations were measured. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and serum alkaline phosphatase (ALP) activities were estimated by conventional methods. Serum and urine GGT activities were also measured. Urine samples were tested by urine dipstick analysis. Results indicated that serum manganese concentration was increased significantly on days 14, 28, 42, 56, and 70 of manganese administration (p < 0.05). The changes in serum enzyme activities ALP, GGT, AST, ALT, and urea and creatinine concentrations during these days were not significant. Changes of urine GGT activity were not significant. Serum TSH, FT3, FT4, T3, and T4 concentrations decreased differently on days 14, 28, 42, and 56 (p < 0.05). Urinalysis by urine dipstick analysis was normal.