Effect of glycogen concentration and form on the response to electrical stimulation and rate of post-mortem glycolysis in ovine muscle

The associations between the muscle glycogen concentration and form and the rate of post-mortem glycolysis in ovine muscle were investigated. Twenty-two merino wethers (18–24 months) were allocated to either roughage or concentrate pelleted diets for 34 days prior to slaughter. An exercise depletion/repletion model was applied four days prior to slaughter to generate differences in muscle glycogen levels at slaughter. Muscle biopsies were taken from the m. semimembranosus (SM) and m. semitendinosus (ST) prior to and immediately after exercise for muscle glycogen determination. At slaughter, one side was electrically stimulated and both sides were conventionally chilled for 24 h. The pH response to electrical stimulation (ΔpH) and the rate of pH decline adjusted to a constant temperature of 38 °C over the initial 6 h post-mortem period was determined in three muscles (m. longissimus thoracis et lumborum LTL, SM and ST). In addition, the concentrations of glycogen, proglycogen (PG), macroglycogen (MG) and lactate in the three muscles immediately after slaughter were determined. The glycogen loss due to exercise was influenced by diet (P ST) and diet (concentrate > roughage). The available glycogen (glycogenA) and MG concentrations at slaughter varied significantly depending on the diet (P SM > ST). Importantly, a positive linear association (P = 0.05) was found between muscle glycogen A concentration at slaughter and the rate of pH decline (temperature adjusted)