FASTING-INDUCED GLYCOGEN DEPLETION IN DIFFERENT FIBER TYPES OF RED AND WHITE-PIG MUSCLES - RELATIONSHIP WITH ULTIMATE PH

The aim of the present work was to study the effect of fasting times ( 0, 24, 48 and 72 h) on glycogen level in different fibre types of a pr edominantly white (Longissimus, LD) and a predominantly red (Semispina lis, SS) pig muscle, and on ultimate pH (pH(u), 24 h post mortem). Thi rty two individually housed Large White castrates (eight pigs per trea tment) were slaughtered individually under minimal stressful condition s. Muscle samples were taken during bleeding for enzymic determination of muscle metabolites and histological examination using computerised image analysis. Myofibres were classified by a combination of metabol ic (W, white; R, red) and contractile (alpha, fast-twitch; beta, slow- twitch) characteristics. The SS showed higher glycogen depletion after 24 h fasting than the LD (-55 versus -26%, respectively). No further significant changes in glycogen level were recorded with enhanced fast ing times (up to 72 h), although in the SS a marked trend towards glyc ogen depletion was observed. Fasting for 24 h resulted in significantl y increased pH(u) in the SS whereas for the LD, a significant increase in pH(u) occurred only after 48 h fasting. In response to fasting, si gnificant decrease in histochemical staining intensity for glycogen oc curred in the three fibre types of the SS. The beta R fibres of the SS showed an almost complete glycogen depletion after 24 h fasting. With increasing fasting time, glycogen was further depleted in fast-twitch fibres (alpha W and alpha R). In the LD, only fast-twitch fibres exhi bited significant decrease in glycogen level after 24 h fasting. Howev er, this was of a much lower magnitude than that observed in the SS an d furthermore, no further variation was recorded with increasing fasti ng time, regardless of fibre type. The present work is the first to re port a significant interaction between muscle type and fasting-induced glycogen depletion in pig. Furthermore, these results demonstrate tha t within each muscle, the extent of fasting-induced glycogen depletion is strongly fibre-type-dependent.