The effect of magnesium on thyroid hormone levels and growth of broilers

30 white Arbor-Acre broilers (15 males; 15 females) aged 4 weeks and weighing 778 +/- 74 g (mean +/- SD) were maintained under identical field conditions, they were exposed to a light: dark cycle of 16 h light: 8 h dark, temperature of 28 degrees C, humidity of 70%. The broilers were randomly divided into 3 groups: The control group (G1, n = 10) was fed standard feed (Mg content 66 mmol/kg dry weight, measured by analysis, protein 19 %, and fat 4 %) and tap water (Mg content 0.29 mmol/L measured by analysis) as drinking water ad libitum. The Mg-normal group (G2, n = 10) and Mg-high group (G3, n = 10) received the same food, but drinking water was enriched with Mg in form of magnesium-L-aspartate hydrochloride (MAH). MAH was added in 2 concentrations, 4 g/L and 8 g/L respectively, yielding approximately 16 and 32 mmol Mg/L. Water was offered ad libitum for 3 weeks. Mg was supplemented in drinking water in G2,G3 until the end of the experiment. Blood collection was done 4 times with heparinized syringes from wingvein of unfasted animals at the starting week (W0), at one week (W1), two weeks (W2), and three weeks (W3) after Mg supplementation. Totally 116 heparinized blood samples were immediately centrifuged at 4,500 rpm for 10 minutes, plasma samples were separated and stored at -20 degrees C until measurements. All samples were analyzed for Mg and Ca with atomic absorption spectrophotometer from Shimadzu Model 680 from Japan, triiodothyronine (T3), and thyroxine (T4) were analyzed by enzymun-test(R) T3 and enzymun-test(R) T4 by using the equipment named Enzymun-Test(R) System ES 700 from Boehringer Mannheim. Data were analyzed statistically using SPSS for window version 6.1.3. At week three of the experiment, broilers in G3 had higher weight gain than G1 and G2. Feed conversion rate was also better in G3 than in G1. Plasma Mg of G2, G3 significantly increased (P < 0.05) during week I to 3 as compared to G1 on the same week while there was no change in plasma calcium. Hormone T3 was significantly increased and higher (P < 0.05) in G3 than G1 at week 1 of the experiment. Plasma T3 level declined during week 2 to week 3 but level of T3 in G2, G3 still were higher than in G1. Plasma T4 was higher in G2 and G3 than G1 (P > 0.05) and the T4 level gradually was increased and was highest at week 2 and decreased at week 3 of the experiment in all groups of broilers. The results suggest that Mg supplementation can increase the level of T3 and T4 in broilers. This increase thyroid hormone may be one of the factors that improve growth in Mg-treated groups.