Total muscle mitochondrial volume in relation to aerobic capacity of horses and steers

Abstract

The relationship between maximal oxygen consumption rate ($\dot V{\text{O}}_{{\text{2max}}}$) and mitochondrial content of skeletal muscles was examined in horses and steers (n=3 each). Samples of the heart left ventricle, diaphragm,m. vastus medialis, m. semitendinosus, m. cutaneous thoracicus andm. masseter, as well as samples of muscles collected in a whole-body sampling procedure, were analyzed by electron microscopy.$\dot V{\text{O}}_{{\text{2max}}}$ per kilogram body mass was 2.7× greater in horses than steers. This higher$\dot V{\text{O}}_{{\text{2max}}}$ was in proportion to the higher total volume of mitochondria in horse versus steer muscle when analyzed from the whole-body samples and from the locomotor muscle samples. In non-locomotor muscles, total mitochondrial volume was greater in horses than steers, but not in proportion to their differences in$\dot V{\text{O}}_{{\text{2max}}}$. The$\dot V{\text{O}}_{{\text{2max}}}$ of the mitochondria was estimated to be close to 4.5 ml O₂·ml⁻¹ mitochondria in both species. It is concluded that in a comparison of a highly aerobic to a less aerobic mammalian species of similar body size, a higher oxidative potential may be found in all muscles of the more aerobic species. This greater oxidative potential is achieved by a greater total volume of skeletal muscle mitochondria.