外源金属硫蛋白对奶牛抗热应激调控及SOD基因表达的影响

将28头泌乳奶牛随机分成A、B、C、D 4组，分别按每头0 (对照)、6.0、12.0和16.0 mg剂量静脉注射经生理盐水溶解的Zn-MT，以探讨外源性金属硫蛋白(MT)对奶牛抗热应激的调控作用及其机理.结果表明：B、C和D组的脉搏、呼吸频率及血清MDA含量均显著(P＜0.05或P＜0.01)低于A组；4%标准乳产量、血液GSH-PX活性、红细胞SOD活性、血清MT含量、奶MT含量及SOD基因表达水平均显著(P＜0.05或P＜0.01)高于A组；C和D组的上述各项指标又优于(P＜0.05或P＞0.05)B组；外源性MT的调控效果以注射后第30天表达最佳.说明MT是一种能够有效调控奶牛热应激能力的生理活性物质，且在奶牛体内表现出一定的剂量效应和时间效应.

Effects of exogenous metallothionein on thermoresistance and SOD gene expression of dairy cattle

To approach the effects of exogenous metallothionein (Zn-MT) on the thermoresistance and SOD gene expression of dairy cattle, an experiment was conducted with 28 lactating cows, which were randomly allocated to groups A, B, C and D, and supplemented with 0, 6.0, 12.0 and 16.0 mg Zn-MT x capita(-1), respectively, by intravenous injection. The results showed that the pulse, breath rate, and serum MDA content of the cows in groups B, C and D were lower (P < 0.05 or P < 0.01), while their milk yield, serum- and milk MT contents, blood GSH-PX activity, erythrocyte SOD activity, and SOD gene expression level were higher (P < 0.05 or P < 0.01) than those in group A. All the test indices of the cows in groups C and D were superior (P < 0.05 or P > 0.05) than those in group B, but no significant difference (P > 0.05) was observed between groups C and D. Exogenous Zn-MT had the best effects on the thermoresistance and SOD gene expression of dairy cattle 30 days after injection. All of these suggested that exogenous Zn-MT should be a physiologically active substance effective to the thermoresistance and SOD mRNA expression of dairy cattle, and presented time- and dose-dependent effects.