In order to reveal the adaptation mechanism of skeletal muscle in yaks to hypoxia, Da-Tong yak at different age stages were selected, and cattle in plain field were selected as control at the same time. The average section area (Ax) , average volume (V) , the numerical density on area (NA) and volume density (Vv, volume density of mitochondria in unit volume of skeletal muscle fiber) of mitochondria in skeletal muscle of Yak and cattle were compared by microstereolgy technology. Results showed that the average section area, average volume of mitochondria in skeletal muscle of DaTong yak declined at first and then increased from birth to adult, and there were significant differences between any two of the groups (P<0. 05). The numerical density on area and the area density increased at first and then decreased from birth to adult, and notable differences can be find between any two of the groups (P<0. 05). The volume density of skeletal muscle mitochondria in DaTong yaks increased following growth, and these parameters mentioned above in DaTong yaks were higher notably than those in plain cattle at the same age (P< 0. 01). According to the results, we can get the conclusions that skeletal muscle of DaTong yak have a perfect histoheredity characteristics at birth and have a fine adaptive ability to plateau hy-poxia environment with characters including smaller muscle fiber diameter, larger surface area density and collagen fiber content, larger microvessel density, more tiny average volume, and higher mitochondria numerical density on area, higher mitochondria area density and higher mitochondria volume density. The structure of skeletal muscle changes continually to promote their growth and to adapt to the environment. Following growth, the muscle fiber diameter and mitochondria volume density increased, but surface area decreased gradually, collagen fiber content and mitochondria numerical density on area increased at first and then decreased, but microvessel density and mitochondria average volume declined at first and then increased. The 30th day of new born yak is a critical stage to get the ability of adaptation for external environment.%为了探讨高原牦牛骨骼肌组织对低氧环境的适应机制,选取大通牦牛作为研究对象,以平原黄牛作对照,通过显微体视学技术比较骨骼肌线粒体的平均截面积(Ax)、平均体积(V)、面数密度(NA,单位面积中线粒体数目)、体积密度(Vv,单位体积骨骼肌纤维中线粒体的体积密度).结果表明,大通牦牛骨骼肌线粒体的平均截面积、平均体积随着年龄的增长,表现为“先降低、再升高”的特点,各年龄段差异显著(P＜0.05)；而面数密度表现为随着年龄增长呈现“由高到低”的变化特点,各年龄段差异显著(P＜0.05)；体密度表现为随着年龄的增长逐渐增加,各年龄段差异显著(P＜0.05)；大通牦牛线粒体与同日龄平原黄牛比,表现为“线粒体小、数量多”的特点,差异极显著(P＜0.01).结果提示,大通牦牛骨骼肌组织线粒体在出生时已获得良好的组织遗传学特性,表现出对高原低氧环境的良好适应性,表现为骨骼肌线粒体平均体积小、面数密度、体密度高的特点；而在个体生长发育过程中,大通牦牛骨骼肌在组织结构及形态学方面表现为多种适应性的变化过程,以满足机体生长发育的需要和对外界环境的适应,表现为骨骼肌线粒体平均体积先降低再升高、面数密度先升高再降低,体密度逐渐增加的特点.其中30日龄是犊牦牛适应外界环境的关键阶段.
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