以含锰超氧化物歧化酶基因表达评价肉鸡对不同形态锰源的生物学利用率

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

目的 通过两个试验研究确定心肌细胞线粒体中MnSOD的基因表达指标是否能更快、更敏感、更恒定地监测出肉仔鸡对不同形态锰源间生物学利用性的差异。方法 试验 (一 )将 5 4 6只商品代 1日龄AA肉公鸡按 4× 4两因子安排的完全随机设计分为 13个处理组 ,每组 6个重复笼 ,分别饲喂不添加锰的食用玉米 -豆粕型基础饲粮 (对照组 )或以无机硫酸锰、弱络合强度的蛋氨酸锰E、中等络合强度的复合氨基酸锰B及强络合强度的复合氨基酸锰C形式添加 0、6 0、12 0、180mg kg锰的试验饲粮 ,试验期 2 1天。 2 1日龄每个重复笼选取 3只与平均体重相近的鸡屠宰 ,立即取出心脏、左侧腿跖骨 ,分析组织锰浓度、心肌细胞线粒体中MnSOD活性及其基因表达。试验 (二 )将 2 70只商品代 1日龄AA肉公鸡随机分为 5个处理组 ,每组 6个重复笼 ,分别饲喂不添加锰的食用玉米 -豆粕型基础饲粮 (对照组 )及分别在对照组饲粮中添加 12 0mg kg锰的 4种锰源试验饲粮。分别于第 7、14、2 1日龄用与试验一相同的方法进行屠宰、组织样品的采集与制备及分析。结果 试验 (一 )中 2 1日龄肉鸡的跖骨灰锰含量、心肌锰含量和心肌细胞线粒体中MnSOD活性均受到饲粮添加锰水平的显著影响 (P =0 0 0 0 1) ,根据这三项指标与饲粮添加锰进食量的多元线性回?

Objective 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. Methods 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 4×4 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 21days. At 21 day of age, three birds from each cage were selected according to average bodyweight of the cage and ki1led. 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 hundreds 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-unsupplenented com-soybean meal basal diet (Control) or the basal diet supplemented with 120mg/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 21th day. The tissues were collected and analyzed as well. Results (1) In experiment 1, ash Mn content, heart Mn content, and MnSOD activity in heart mitochondria on the 21th 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 21th 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 14 day or 21 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. Conclusion 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.