Effect of lead on thyroid function in sheep

The objective of this experiment was to determine the effect of long-term low-dose administration of lead (Pb) on thyroid function in sheep. In this experiment 10 healthy Iranian male sheep, aged about one-year-old were randomly allocated into two equal groups of control (n = 5) and experiment (n = 5). Both groups were kept under the same conditions of food and environment. The treatment group received lead acetate (5 mg/kg/day) orally for 8 weeks. Blood sampling of two groups was done on the same days, on days 0 (before receiving lead acetate in treatment group), 14, 28, 42, 56 and 70 after lead administration, every morning (8 to 9 a.m.). The function of the thyroid was evaluated by measuring the levels of serum thyroid hormones T3, T4, FT3, FT4 and TSH. The hepatic function in both groups was evaluated by measuring hepatic enzyme activities including alanin amino transferase (ALT), aspartate aminotreansferase (AST), γ glutamyl transferase (GGT), and total bilirubin (TBIL). Serum levels of T3 (on days 14, 56 and 70) T4 (on days 14, 28, 42, 56 and 70), FT3 (on days 56 and 70), FT4 (on days 42, 56 and 70) and TSH (on days 14, 28, 42, 56 and 70) significantly decreased in lead-treated sheep when compared to the control group (P<0.05). Serum enzyme activities of ALT (on days 28 and 42), AST (on days 28, 42, 56 and 70) and TBIL (on days 28 and 70) in Pb treated sheep increased significantly in comparison with the control group (P<0.05). Our findings suggest that Pb exposed sheep can be at risk of low thyroid function.