The effect of exogenous MT on lymphocyte apoptosis of the dairy cow was studied in vitro under heat stress. The splenic dairy cow lymphocytes were divided into 4 groups which had final concentrations of MT 0 (control group), 70 (group Ⅰ ), 140 (group Ⅱ ) and 210 μg/mL (group Ⅲ). The cells of each group were cultured in a cell incubator (37℃, 5%CO2). After 20 h, the cells of each group were put into water bath pot (43℃) for 1 h, and then recultured in a cell incubator (37℃, 5%CO2) for 3 h. Finally, various indexes were teste...