Study On The Optimal Manganese (Mn) Level In A Practical Diet For Broiler Chicks

The experiment was conducted with a total of 480 Arbor Acres (AA) commercial male broilers at the age of one day old to study the effect of dietary Mn level on growth performance, incidence of leg abnormality, tissue Mn content, MnSOD activity in heart mitochondria, and its gene expression on D 7, 14 or 21. The aim of the study was to find the quickest and most sensitive indices and determine the optimal dietary Mn level for broiler chicks, so as to evaluate the optimal dietary Mn level for AA broiler chicks before 21 days old. The birds were randomly allotted by bodyweight to one of eight treatments (five pen replicates of twelve each) in a completely randomized design, and fed a Mn-unsupplenented corn-soybean meal basal diet (Control, 18.5mg/kg Mn) or the basal diet supplemented with 20,40,60,80,100,120 mg/kg Mn as Mn sulfate, for 21 days respectively. The results showed that: (1) There were no difference (P>0.22) in growth performance of broilers between treatments; (2) There were no leg abnormality difference observed during D 1-7 and D 8-14. While during D 15-21, the birds in the control group treated and supplemented with 20,40,60 mg/kg Mn had a higher (P<0.08) incidence of leg abnormality than other Mn-supplemented groups; (3) There were differences (P<0.01) in tissue Mn content, the concentrations of Mn in pancreas and hearts correlated with the diet Mn level were quadratic curves (P<0.05) or asymptotes(P<0.01 ).When the concentrations of Mn in pancreas reach the require level, the range of diet Mn level was on 120-140mg/kg, but when the concentrations of Mn in hearts reach the require level, the range of diet Mn level was narrow (103-109mg/kg). The concentrations of Mn in liver of D 7 correlated with the diet Mn level was linearity(P<0.01) ,so it was not suitable for evaluating the dietary Mn level for AA chickens. The concentrations of Mn in liver of D 14 and D 21 correlated with the diet Mn level was quadratic curves (P<0.02), When the concentrations of Mn in livers reach therequire level, the range of the diet Mn level of the diet for the birds was 108-119mg/kg, The results indicate that the concentrations of Mn in livers could be quicker, more sensitive, and more stable than that of pancreas and hearts. Based on the concentrations of Mn in hearts, 100-110 mg/kg Mn in diet would be a satisfactory level for AA broilers. (4) There were significant differences (P<0.01) in MnSOD activity of heart mitochondria, and its gene expression between treatments ( P<0.01) . MnSOD activity in heart changed with chicks'age, and the range of Mn level in the diet based on the MnSOD activity in heart was broad (116-137mg/kg), while the level of MnSOD mRNA has no difference between different ages, and the range of the diet Mn level was narrow(111-113mg/kg). So the level of MnSOD mRNA could be quicker and more sensitive than MnSOD activity. Based on MnSOD mRNA level in hearts' mitochondria, 110 mg/kg Mn in diet would be a satisfactory level for AA broilers. The estimation of dietary Mn level based on heart MnSOD mRNA level could request a shorter time of experimental period and smaller number of animals, and thus less cost than before. This finding has not been reported in any literature before.In conclusion, dietary Mn level significantly affected tissue Mn content, MnSOD activity in heart mitochondria, and its gene expression in broilers pretranslationally; but heart MnSOD mRNA level was the quickest, most sensitive and most stable indices based on the chicks'age and the dietary Mn level ranges gained from these indices, it could be a new method for a quick and effective assessment in detecting the optimal dietary Mn level for broiler chicks.