The effects of relative gain and age on peripheral blood mononuclear cell mitochondrial enzyme activity in preweaned Holstein and Jersey calves

Mitochondria are central to metabolism, nutrition, and health, but many factors can influence their efficiency. The objectives of this study were to determine if the mitochondrial enzyme activities of citrate synthase, complex I, complex IV, and complex V from peripheral blood mononuclear cells in Holstein and Jersey dairy calves were affected by age or relative gain as a percent of initial weight. Twenty-three Holstein and 23 Jersey heifer calves were enrolled between 3 and 6 d of age and whole blood samples were collected via jugular venipuncture at 1, 2, and 8 wk of age. Crude mitochondrial extracts were obtained from the peripheral blood mononuclear cell fraction at each time point and subsequently assayed for enzymatic activity. Age-dependent changes in activity were observed in complex V for both breeds. In Jersey calves complex IV and citrate synthase activity differed with age. Complex I activity was greater for high relative gain Jerseys and tended to be greater for high relative gain Holstein calves. Holstein calves had greater incidence of scours compared with Jersey calves, and in both breeds scouring calves exhibited greater complex V activity compared with those without scours. These data suggest that age and immune challenge in the form of scours affect mitochondrial complex V activity. Additionally, complex I activity may serve as a marker for calf growth potential because it was influenced by relative gain and not age.