Live changes in muscle glycogen concentration of steers due to feeding and fasting as determined through serial biopsies of the Longissimus dorsi muscle
Insufficient glycogen content in bovine muscle at slaughter produces meat with high final pH (> 5.8) which is undesirable. The objective of this study was to determine through biopsies the live changes in muscle glycogen concentration (MGC) of housed steers fed on hay or hay plus energy concentrate for 30 d and then determine the effect of food deprivation (fasting) for 24 h on the same variable. Ten steers of similar age, weight, and phenotypic characteristics were housed in individual pens and randomly assigned to two feeding treatments: ad libitum hay only (H, n = 5) and ad libitum hay plus flaked corn (Zea mays L.) (HC, n = 5). Biopsies (B) were taken from the Longissimus dorsi muscle at four occasions: the day before the start of experiment (B0), after 15 d (Bl), after 30 d (B2), and fasted for 24 h after B2 (B3). Before each biopsy, steers were sedated with xylazine (0.03 mL kg-1) and lidocaine was applied locally; samples were frozen in liquid nitrogen to determine MGC. Results showed a significant (P < 0.05) effect of diet treatment (HC > H) and also of time (B2 > Bl) on MGC; the decrease in MGC of steers due to fasting (B2 vs. B3) was not significant (P > 0.05). It was concluded that muscle biopsies allowed to detect a difference in the increase of MGC in steers fed an energy supplementation compared to steers fed hay only, and that fasting for 24 h tended to reduce MGC in both groups.