The effects of dietary replacement of inorganic iodine with organic source on growth performance, carcass characteristics, meat iodine content, thyroid hormones and some blood indices in broiler chickens

The replacement of inorganic mineral with organic sources can impose benefical effects on broiler chickens. The replacement of 25 and 50% inorganic iodine with organic source had beneficial effects on the determined indices of current experiment (Angelovicova et al., 2012). Higher replacement levels (100% organic iodine) detrimentally affected the blood and tissue indices of broiler chickens (Opalinski et al., 2012; Saki et al., 2012; Peyvastegan et al., 2017). The aim of this study was to investigate the replacement of inorganic mineral with organic sources iodine effects on performance, carcass characteristics, meat iodine, thyroid hormones, and some blood indices in broiler chickens. This experiement was performed to investiage the effects of different levels of inorganic iodine (potassium iodiate) replaced with organic source (yeast iodine) on performance, carcass characteristics, iodine content of meat, and thyroid hormone concentrations and blood indices (hematocrit, RBC, WBC, Hb, ALP, ALT, AST, cholesterol, triglyceride, HDL, LDL) in broiler chcikens. The experiment was done based on a completely randomized design using 250 male broiler chickens (Ross strain) with 5 treatments and 5 replicates per each treatment (10 birds per each replicate) during a 42 days period. The experimental treatments included different replacement levels of 0.0 (5 mg/kg inorganic iodine without any organic source), 0.25 (3.75 mg/kg inorganic iodine along with 1.25 mg/kg organic source), 0.50 (2.5 mg/kg inorganic iodine along with 2.5 mg/kg organic source), 0.75 (1.25 mg/kg inorganic iodine along with 3.75 mg/kg organic source) and 100% (5 mg/kg organic iodine without any inorganic source) inorganic iodine (potassium iodiate) with organic source (yeast iodine). None of the repleacement levels of inorganic with organic source had effects on feed intake, weight gain and feed conversion ratio (P>0.05). Inceasing the inorganic replacement with organic form of iodine linearly increased the carcass and thigh relative weight (P<0.05). The birds fed 5 mg/kg inorganic iodine had the highest carcass weight (P<0.05). The birds fed the diets including 75 and 100% of organic iodine replacement had the highest breast and thigh weights (P<0.05). The abdominal fat trended to be lower in birds fed 5 mg/kg organic iodine (100% replamecment) as compared to control diet (100% inorganic iodine), (P=0.065). Moreover, increasing the replacement amount of organic iodine to 100% increased the breast meat iodine content linearly (P<0.05), while breast meat of birds fed 5 mg/kg organic iodine had the highest iodine content (P<0.05). Moreover, the breast iodine content of birds fed the diets with 75% replacement of inorganic iodine (3.75 mg yeats iodine and 1.25 mg potasium iodate per kg) was higher than those of diets with lower inorganic iodine replacements (P<0.05). No effects of inorganic iodine replacement were detected on relative weights of liver, heart, spleen, small intestine, deudenum and ileum (P>0.05), but incressing replacement of organic iodine caused an increase in the relative weights of pancreas, gizzard, jujenum, and thyroid gland (P<0.05). Birds which received the highest replacement level of organic iodine showed the highest pancrease,
gizzard, jejunem and thyroid gland weights wherease the control birds had the lowest weights of these organs at day 42 of experiment. There were no effects of inorganic iodine replacement with organic source on white blood cells, lymphocytes, monocytes, basophils, eosinophils and hetrophils at day 42 of experiment (P>0.05). Moreover, increasing the organic iodine replacement to inorganic form increased red blood cells and hematocrit (P<0.05). Blood hematocrit was increased by increasing the organic replacement until 50% (P<0.05). No effects of replacement level were observed for blood triglyceride and cholesterol (P>0.05). Both the blood LDL and HDL contents were affected by the replacement levels (P<0.05). Blood LDL concentration was increased by increasing the inorgainic level replacements but there were no significant difference between the replacement levels of 50, 75 and 100% inorganic iodine. The highest blood HDL concentration was related to the birds fed the 50% replacement of inorganic iodine with organic iodine source (2.5 mg yeast iodine and 2.5 mg potassium iodate). Moreover, the lowest blood HDL content was observed for the birds fed 75% replacement of inorganic iodine with organic iodine source. The blood enzyme activities of alanine amino transferase, aspartate amino transferase and alkaline phosphatase along with T3 and T4 contents were increased by increasing the replacement level of inorganic iodine with organic source (P<0.05). The birds fed the control diet (5 mg/kg potassium iodate) had the lowest enzyme activities and thyroid hormone contents while the highest activity of the mentioned enzymes and thyroid hormones were observed for the higest replacement rate (100% inorganic iodine replacement). It is concluded that higher than 50% inorganic replacement with yeast iodine caused functional impairment of vital organs. Hence, replacement of 25 and 50% inorganic iodine with organic form had the benefical effects in broiler chickens by increasing the carcass and thigh weights, the breast iodine content and relative weights of internal organs.