The impact of nutrition on bovine muscle glycogen metabolism following exercise

The aims of this study were to develop a muscle biopsy technique which impo sed minimal stress on cattle, enabling accurate monitoring of muscle glycog en concentration; to develop a method based on exercise, for controlled dep letion of glycogen from muscle; and to utilise the model to determine the a bility of cattle on hay and cereal grain diets to replete muscle glycogen. Expt 1 established the influence of repetitive muscle biopsies on muscle gl ycogen concentration. It consisted of 3 trials in which cattle received 4 s erial biopsies every 36 h over a 108-h period. Repetitive biopsy had minima l impact on M. semimembranosus (SM) glycogen concentrations, although it di d reduce concentration in the M. semitendinosus (ST), particularly when ani mals were penned individually. Expt 2 established an exercise regimen in wh ich cattle were trotted at 9 km/h for five 15-min intervals, with 15 min re st between each interval, depleting muscle glycogen by approximately 50%. E xpt 3 determined the repletion rates of muscle glycogen, by utilising the e xercise/biopsy model. Cattle were allocated to 4 dietary treatments: hay, s ilage, hay-barley, and hay-maize. The metabolisable energy (ME) of these ra tions ranged from 8 to 11.3 MJ/kg. After the exercise regimen, glycogen con centration 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 ref ractory to glycogen repletion over the same period. Both the SM and ST of t he cattle on the hay diet showed no significant repletion following exercis e. Repletion following exercise demonstrated a positive linear relationship with ME intake.