选取16头泌乳荷斯坦奶牛，根据年龄、胎次、泌乳时间和产奶量等进行配对，随机分为对照组和试验组，试验组奶牛每天每头补饲12 g过瘤胃蛋氨酸，研究夏季热应激下补饲过瘤胃蛋氨酸对奶牛生产性能、血液生化指标、淋巴细胞凋亡以及相关基因表达的影响。淋巴细胞凋亡采用流式细胞仪检测，Bcl-2和Bax mRNA采用定量PCR测定。结果发现：与对照组相比，夏季奶牛饲喂12 g/d过瘤胃蛋氨酸，有提高产奶量、乳脂率、乳蛋白、乳糖和非脂固形物的趋势；体细胞数呈下降趋势；奶牛血液中谷丙转氨酶、谷草转氨酶和磷酸肌酸激酶均有所下降，但差异均不显著（P>0.05）；乳酸脱氢酶水平下降了10.37%，差异显著（P<0.05）。碱性磷酸酶、葡萄糖、超氧化物歧化酶和谷胱甘肽过氧化物酶呈增加趋势，丙二醛水平降低，但差异均不显著（P>0.05）。与对照组相比，饲喂12 g/d过瘤胃蛋氨酸组，奶牛外周血液淋巴细胞凋亡率降低了36.39％，差异极显著（P<0.01）；瘤胃蛋氨酸组奶牛外周血液淋巴细胞Bcl-2 mRNA基因丰度提高了11.92%；Bax mRNA基因丰度下降了17.30%；Bcl-2 mRNA与Bax mRNA比值提高了36.36%，但差异均不显著（P>0.05）。以上结果表明夏季奶牛补饲过瘤胃蛋氨酸可以提高奶牛生产性能，清除体内自由基，减少外周血液中淋巴细胞凋亡，上调抗凋亡基因和抑制促凋亡基因表达，有缓解热应激的作用。

Sixteen cows were divided into control and trial group according to age, parity, calving days and milk production. Cows were supplemented with 12 g/d rumen protected methionine (Met) in the trial group. Effects of rumen protected Met on performance and the apoptotic rate of blood lymphocytes and expression of apoptosis related genes in dairy cows in summer were studied. The apoptotic rate of lymphocytes was analyzed by flow-cytometry. The gene abundance of Bcl-2 mRNA and Bax mRNA were analyzed by quantitative RT-PCR in the blood lymphocytes. The results showed that supplementing 12 g/d rumen protected Met could improve tendency of milk yield, mild fat, milk protein, lactose and non-fat solid content. Somatic cell had the decreased tendency when supplementing 12 g/d rumen protected Met. Supplementing 12 g/d rumen protected Met could decrease the level of glutamate pyruvate transaminase (GPT), glutamic oxalacetic transaminase (GOT) and creatine phosphokinaxse (CPK) of plasma compared with control group but there were no significant differences in these indices (P>0.05). The level of LDH of plasma decreased by 10.37% than that in control group and the difference was significant (P<0.05). The levels of ALP, GLU, SOD and GSH-Px were improved while MDA was decreased than that in control group but the differences were not significant (P>0.05). The apoptotic rate of lymphocytes decreased by 36.39% in supplementing 12 g/d rumen protected Met group than that in control group and the difference was significant (P<0.01). The abundance of Bcl-2 mRNA of lymphocytes was improved by 11.92% and the abundance of Bax mRNA was decreased by 17.30% in trial group than that of control group. The ratio of Bcl-2 mRNA to Bax mRNA was increased by 36.36% in trial group than that in control group but the difference was not significant (P>0.05). It was concluded that supplementing 12 g/d rumen protected Met could improve performance, scavenge free radicals, decrease apoptotic ratio of lymphocytes, control expression of apoptosis related genes and moderate heat stress in dairy cows in summer. ［Chinese Journal of Animal Nutrition, ２００9，２1（5）:665-672］