Metabolic conditions in Porcine longissimus muscle immediately pre-slaughter and its influence on peri- and post mortem energy metabolism.

To clarify the physiological prerequisites for the course of energy metabolism post mortem, 80 pigs consisting of four females from each of 20 litters of crossbreeds (Duroc as sireline and Danish Landrace×Danish Large White as dam line) were within litter allocated to four different treatments (A, B, C and D) to provide a large variation in the concentration of the key metabolites glycogen, ATP and creatine phosphate at the time of stunning. (A) no stress before stunning, (B) physical stress consisting of treadmill running (3.8 km/h for 10 min) immediately before stunning, (C) intermediate reduction of glycogen at stunning achieved by application of adrenaline (0.2 mg/kg live weight 15-18 h before stunning), and (D) maximal reduction of glycogen achieved by application of adrenaline (0.3 mg/kg live weight 15-18 h before stunning) and treadmill running (3.8 km/h for 5 min). Compared with resting values (measured in samples taken in the pen the day before slaughter by needle biopsy), longissimus muscle glycogen (16, 13, 57 and 66% for A, B, C and D, respectively), creatine phosphate (17, 22, 12 and 9% for A, B, C and D, respectively) and ATP levels (10, 15, 38 and 31% for A, B, C and D, respectively) measured immediately before stunning were all reduced by the treatments. Stunning caused a rather uniform reduction in creatine phosphate level in all the models. Glycogen concentrations were also further reduced in treatments A, C and D, but not in B, and although ATP levels increased in all the models during stunning, this was only significant for the B model. Consequently, the effect of CO(2) stunning on glycogen and ATP levels depends on pre-slaughter handling. It was also shown that an inverse relationship between ultimate pH and glycogen concentration at the time of stunning existed only when glycogen levels at stunning were below 53 mmol/kg (r=0.88, P<0.001). The validity of this threshold value is discussed. Furthermore, the possibility to standardise the physiological prerequisites of the post mortem pH decreases represents a potent tool to investigate metabolic causes of variations in meat quality characteristics.