Dark-cutting in muscles of the beef carcass is due to low muscle glycogen levels at slaughter and occurs particularly in autumn and winter in grass-fed cattle in southern Australia. The aim of these experiments was to investigate the effect of supplementary feeding of cattle grazing pasture during winter on muscle glycogen levels. The first experiment involved 70 cattle allocated to two stocking rates grazing improved perennial ryegrass and subterranean clover pastures [high stocking rate (HSR) v. low stocking rate (LSR)] by two pasture feeding regimes (control, pasture only v. pasture supplemented with a high-energy ration for 4 weeks) plus a feedlot treatment (fed high-energy ration in pens with no pasture for 11 weeks). Muscle biopsies were collected from the M. semitendinosus (ST) and M. semimembranosus (SM) muscles and analysed for muscle glycogen. The ST muscle glycogen content for supplemented animals increased (P < 0.05) over the feeding period but there was no effect (P > 0.05) of supplementation on the muscle glycogen content of the SM or on the muscle glycogen content of the ST or SM of cattle in the feedlot treatment, relative to control cattle. HSR cattle tended to have lower muscle glycogen in the ST compared to LSR cattle across both feeding regimes. The second experiment used 60 cattle allocated to two treatments (control, pasture only v. pasture supplemented with a high-energy ration for 3 weeks). The treatments were applied to cattle grazing improved perennial ryegrass and subterranean clover pastures and muscle biopsies were collected weekly from the SM and ST. Supplementation resulted in a linear increase (P < 0.05) in muscle glycogen levels over the 3 weeks in both the SM and ST muscles. These results indicate that feed quality has a major impact on muscle glycogen levels in the SM and ST of cattle destined for slaughter. At times of the year when pasture quality is poor or quantity is lacking, supplementation with a high-energy supplement has the potential to dramatically increase muscle glycogen and reduce the incidence of dark-cutting beef.