中文摘要：

将28头泌乳奶牛随机分成A、B、C、D4组，分别按每头0（对照）、6．0、12．0和16．0mg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．

英文摘要：

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 ·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, serumand 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.