[Bioavailabilities of manganese sources based on heart manganese-containing superoxide dismutase gene expression for...

Two experiments were conducted to determine whether heart manganese-containing superoxide dismutase (MnSOD) gene expression could detect the differences in bioavailabilities of Mn sources more quickly, sensitively and constantly than other indices.

In experiment 1, a total of 546 day-old commercial male Arbor Acres (AA) broilers were randomly assign to each of thirteen treatments with six cage replicates according to a completely randomized design involving a 4 x 4 factorial arrangement. Each group of birds was fed Mn-unsupplemented corn-soybean meal basal diets (Control) or basal diets supplemented with 60, 120 or 180 mg/kg Mn as either Mn sulfate, Mn-Met E, Mn-AA B or Mn-AA C for 21 days. At 21 days of age, three birds from each cage were selected according to average bodyweight of the cage and killed. Heart and left leg were excised immediately. Mn concentrations in tissues, MnSOD activity and gene expression of MnSOD in heart were analyzed. In experiment 2, two hundred and seventy day-old AA commercial male broilers were randomly allotted to one of five treatments with six cage replicates in a completely randomized design, and fed a Mn-unsupplemented corn-soybean meal basal diet (Control) or the basal diet supplemented with 120 mg/kg Mn as each of the four Mn sources in experiment 1 for 21 days. The methods in experiment 1 were used to select and slaughter birds from each cage on the 7th, 14th or 21st day. The tissues were collected and analyzed as well.

(1) In experiment 1, ash Mn content, heart Mn content, and MnSOD activity in heart mitochondria on the 21st day were affected (P = 0.0001) by dietary added Mn level. Based on slope ratios from multiple linear regressions of these three indices on dietary added Mn intake, the relative bioavailabilities of organic Mn sources did not differ from that of MnSO4 (P > 0.14). Heart MoSOD mRNA level on the 21st day was affected by both Mn source (P < 0.10) and Mn level (P = 0.0001). Based on slope ratios from the multiple linear regression of heart MnSOD mRNA level on dietary added Mn intake, if 100% was set for Mn sulfate, the relative bioavailabilities of organic Mn sources with weak, moderate, and strong chelation strengths were 99.0%, 132.3% and 112.7%, respectively. The organic Mn source with the moderate chelation strength was more available (P < 0.05) than Mn sulfate and organic Mn sources with the weak or strong chelation strengths; (2) In experiment 2, the seven day-old chicks fed on the diet supplemented with the organic Mn source with the moderate chelation strength showed a higher (P < 0.02) MnSOD mRNA level than those fed on the diets supplemented with Mn sulfate and the organic Mn source with the weak chelation strength, and the same tendency was observed on the 14th day or 21st day (P < 0.05). Ash Mn content and heart MnSOD activity were less sensitive in detecting the differences among Mn sources in bioavailability than MnSOD mRNA level.

The results indicate that dietary Mn significantly affected heart MnSOD gene expression pretranslationally, and heart MnSOD mRNA level as early as on the 7th day could detect differences in bioavailabilities of Mn sources more quickly, sensitively and constantly than all other indices. There was a close correlativity between chelation strengths of these organic Mn sources and their relative bioavailabilities for broilers, in which the organic Mn source with the moderate chelation strength was the most available. The estimation of relative bioavailabilities of Mn sources based on heart MnSOD mRNA level could request a shorter time of experimental period and smaller number of animals, and thus could be a new method for a quick and effective assessment in bioassays of Mn sources for broilers.