Glycogen metabolites and meat quality in feed-restricted re-fed beef heifers

Twenty-four Hereford crossbred heifers weighing 222 kg (22 kg SD) and aged 226 d (13 d SD) on day 0 were used to investigate the effects of feed restriction (period 1) followed by realimentation (period 2) on hepatic and longissimus muscle glycogen metabolites and meat quality. The heifers were randomly assigned in equal numbers to either ad libitum feeding (ADLIB) or maintenance feeding for 92 d followed by realimentation (REST), and serially slaughtered over a wide range of liveweights (200-460 kg). The concentrations of glycogen, its metabolites, and the total glucidic potential (GP) were determined from portions of the caudate lobe of the liver and the longissimus lumborum (LL) muscle. Meat quality assessment of the longissimus thoracis (LT) was done by objective means. Hepatic glycogen concentration was lower (P = 0.05) in REST than in ADLIB heifers, and GP tended to show a similar pattern (P = 0.07). There were no significant differences in the concentrations of glycogen or its metabolites in the LL of REST compared with ADLIB heifers. However, the heifers slaughtered during period 1 had lower muscle glycogen (P = 0.04) and higher lactate (P < 0.01) concentrations than those slaughtered during period 2. REST heifers had lighter slaughter weights resulting in smaller ribeye areas (P = 0.03), lower intramuscular fat concentration (P < 0.01) and higher moisture content (P < 0.01). Independent of slaughter weight, REST heifers had higher drip loss (P = 0.05) and lower L * (P = 0.01) than ADLIB heifers. These results suggest that feed restriction affects hepatic glycogen reserves and also has minor effects on meat quality traits in beef heifers. However, there was no indication that meat from REST heifers had severe quality defects such as DFD (dark, firm, dry) meat.