Study On An Optimal Maganese (Mn) Level In A Practical Diet For Brown-Egg Layers

An experiment was conducted using a total of 120 20-week old Beijing Red commercial layers to study the optimal Mn level in a practical diet for brown-egg layers during a phase of 20?3 weeks. Layers were randomly allocated by body weight to one of five treatments according to the completely randomized design. and fed a basal cornsoybean meal diet containing 2oppm Mn and the basal diets supplemented with 30, 60, 90 or l2Oppm Mn as reagent grade Mn504?H20, respectively. Layers were allowed ad libitum access to feed and tap water.Dietary Mn level had no effect (P>0.l0) on egg production rate, egg weight. egg yield, daily feed intake, feed/egg ratio, egg shape index, haugh unit, eggshell percentage, eggshell thickness, and serum antibody titer against Newcastle Disease Vaccine (NDV), but affected eggshell strength(P<0.0l), Mn contents in heart, pancreas and spleen (P<0.10), and Mncontaining superoxide dismutase (MnSOD) activity (P<0.00l) in heart mitochondria.As dietary Mn levels increased, eggshell strength, Mn contents in heart, pancreas and spleen, and MnSOD activity in heart mitochondria increased in an asymptote or in a quadratic curve. Broken-line model (P<0.05) of eggshell strength, quadratic curve model (P<0.03) of heart Mn content, and asymptote model (P<0.00l) of MnSOD activity in heart mitochondria could be well fitted with dietary Mn levels, respectively. Dietary Mn levels required to obtain satisfactory eggshell strength, heart Mn content, and MnSOD activity in heart mitochondria based upon the above best fitted models were 45, 100, and lOSppm.respectively.In addition, the effect of dietary Mn level on eggshell ultrastructures, plasma biochemical indices(glucose, albumin, globulin, cholesterol, triglyceride, phosphatide, uric acid, alkaline phosphatase, creatine phosphokinase, glutamate oxalacetate transam inase, and glutamate pyruvate transaminase), the content of other mineral elements (Ca, Mg. Na. K. Cu, Fe, and Zn) in heart, pancreas and spleen. CuZnSOD activity in heart, and both MnSOD and CuZnSOD activities in liver was also observed in this study.The results from this study indicate that Mn content in heart and MnSOD activity in heart mitochondria. especially MnSOD activity in heart mitochondria, are the specially sensitive indices to evaluate Mn requirements of layers: And the lOSppm Mn in the basal corn-soybean meal diet should be a satisfactory level for 20?3 week-old brown-egg layers at the average daily feed intake of 113g. which is 3.75 times of the amount (28ppm) recommended by NRC(1994) in Nutrient Requirements of Poultry.