The relative effect of dietary energy density on repleted and resting muscle glycogen concentrations

The aim of this study was to assess the effect of dietary energy density on the glycogen concentration of bovine gluteus medius (GM) and longissimus thoracis et lumborum (LTL) muscles in castrated and intact males. Cattle received diet C (90% whole corn and supplement: 10% alfalfa haylage) or diet AH (100% alfalfa haylage) in three experiments involving a 2×2 factorial cross-over design. Cattle fed an AH diet for 70 days prior to the first experiment had high glycogen concentrations in the GM (129±9.9 mmol/kg) and LTL (108±7.6 mmol/kg) at the first biopsy session. These concentrations are similar to GM (133±6.2 mmol/kg) and LTL (105±5.8 mmol/kg) glycogen concentrations when these cattle subsequently received diet C for 30 or 37 days. Diet C increased muscle glycogen concentration, but the consistency of the increase in glycogen was dependent on the initial concentration. When the initial glycogen concentration was depleted to 50 μmol/g with one subcutaneous injection of adrenaline, repleted glycogen concentration was higher for diet C than AH (P<0.01) in all comparisons involving GM and LTL muscles of both steers and bulls. For resting muscle glycogen, the GM of bulls was more sensitive to the effect of diet C than the bull LTL or either muscle in steers. Diet was not a major determinant of resting muscle glycogen concentration. The ultimate pHs of GM, LTL and semimembranosus (SM) were not affected by diet and residual glycogen was lower in LTL of bulls fed either diet than for LTL of steers fed AH. Diet and male status did not affect residual glycogen in GM or SM.