The effect of time off feed prior to slaughter on muscle glycogen metabolism and rate of pH decline in three different muscles of stimulated and non-stimulated sheep carcasses

The aim of this study was to determine the effect of time off feed ( TOF) prior to slaughter on muscle glycogen metabolism and rate of pH decline in sheep muscle. All animals were maintained on a roughage diet for 6 weeks and were then subjected to either 0, 2, or 4 days TOF with access to water, prior to slaughter. Glycogen concentrations were determined post-slaughter for 3 different muscles, M. longissimus thoracis et lumborum ( LTL), M. semimembranosus ( SM), and M. semitendinosus ( ST), as well as measuring pH declines for all animals in each of the 3 muscles under both electrically stimulated and control conditions. Ultimate pH values ( pH(u)) were determined 48 h post- slaughter. Both the 2- day and 4- day TOF groups lost liveweight during their curfew period, whereas the control (0- day) group gained weight. TOF had no effect on post- slaughter carcass characteristics, muscle glycogen concentrations, pHu, or rate of pH decline. Increased muscle glycogen concentrations resulted in faster rates of pH decline. This response was curvilinear, plateauing at a glycogen concentration of about 56 mmol/ kg muscle. Muscle glycogen concentration also affected the response of pH decline to electrical stimulation, interacting with muscle and pre- stimulation pH. Low muscle glycogen levels limited delta pH only in the SM and ST and only in muscles of lower pre- stimulation pH.