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

Abstract

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 (pHu) 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.