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

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.