Impact of dietary potassium levels on muscle glycogen concentration
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The aim of the current study was to evaluate the impact of dietary potassium on muscle glycogen concentrations in an effort to determine which pathway is driving the increased incidence of dark cutting in beef cattle. Eighteen Angus steers, approximately 15 months old, with an average live weight of 441±28 kg were used. The animals were randomly split into Low (1.5%), Medium (2.7%) and High (3.8%) dietary potassium (K) levels. The diets were balanced to compare the three different K levels, with minerals and metabolizable energy remaining constant for an average daily gain of 1 kg according to NRC (2016). Muscle biopsy 1 on day 0 were taken from the Longissimus (LT), Semitendinosus (ST) and Semimembranosus (SM) muscles. On day 3, the steers were exercised for 120 minutes before the biopsies were taken, while on days 6 and 9 biopsies were also taken. Glycogen and lactate concentrations were measured for all biopsies. There were no effect of K treatment on glycogen and lactate concentrations for the three analyzed muscles. However, the glycogen concentration values for SM was about 24.2 and 18.7% greater than ST and LT, respectively. The lactate concentration was on average 43.7% higher in biopsy 1 compared with the average of biopsies 2, 3 and 4 for LT, while for ST and SM, biopsy 1 was on average 25.0% higher than the average for biopsies 2, 3 and 4.