The impact of nutrition on bovine muscle glycogen metabolism following exercise

Abstract

The aims of this study were to develop a muscle biopsy technique which imposed minimal stress on cattle, enabling accurate monitoring of muscle glycogen concentration; to develop a method based on exercise, for controlled depletion of glycogen from muscle; and to utilise the model to determine the ability of cattle on hay and cereal grain diets to replete muscle glycogen. Expt 1 established the influence of repetitive muscle biopsies on muscle glycogen concentration. It consisted of 3 trials in which cattle received 4 serial biopsies every 36 h over a 108-h period. Repetitive biopsy had minimal impact on M. semimembranosus (SM) glycogen concentrations, although it did reduce concentration in the M. semitendinosus (ST), particularly when animals were penned individually. Expt 2 established an exercise regimen in which cattle were trotted at 9 km/h for five 15-min intervals, with 15 min rest between each interval, depleting muscle glycogen by approximately 50%. Expt 3 determined the repletion rates of muscle glycogen, by utilising the exercise/biopsy model. Cattle were allocated to 4 dietary treatments: hay, silage, hay–barley, and hay–maize. The metabolisable energy (ME) of these rations ranged from 8 to 11.3 MJ/kg. After the exercise regimen, glycogen concentration repleted in a linear fashion over 72 h in the SM of the animals fed maize, barley, and silage. In contrast, the ST of these animals was refractory to glycogen repletion over the same period. Both the SM and ST of the cattle on the hay diet showed no significant repletion following exercise. Repletion following exercise demonstrated a positive linear relationship with ME intake.