Post-mortem changes in the skeletal muscle of the fowl (Galus domesticus)

Abstract

The Mstoeheaioal and histological feetores of the pectoralie sad iliotibl&lie muscles of the fowl (Oellug domesticus) have been examined in unfisou. and fixed tissue using the light and tranei&ieedon electron microscopes. Ml t -o fibre* of the pectoi --lie .liuocie show high myosin t.deuooine triphosphatase (myosin ATPcm) and glycogen phoephorylate (Chase) activities and low succinate dehydrogenase (bJilaec; activity. 'Two types of fibre can be differentiated in the iliotibialie muscle, one of which is low in myosin ATPaee and Chase activities and moderate to hi$h in GOHase activity, and the other ie high in myosin AiPam and Ukase activities with a complete range of ShHase activity from low to high in different fibres.The ultrastruoture of Doth muscles is typical of vertebrate twitch muscle. The pectoralio oaa thin disks, few mitochondria and » poorly developed earcotubular system relative to the iliotibialis. In iliotibialie the 4 disk© are thicker and more variable, the overall content of mitochondria is higher, although there is wide variation between fibres, and the sarcotubular system is extensive. Correlation of the ultrnetructural and hiBiochemical features has been attempted.Tito observations indicate that the pectoralis muscle has a low overall capacity for aerobic metabolism in contrast with the iliotibialis muscle, which has a high overall capacity for aerobic metabolism. Change in the histology of these two muscles has seen compared at 0.5, 1, 1.5, 4, 8 and 24 hours post-mortem during stotasge of chicken carcasses at 40°C.Unfixed and fixed samples of both muscles show kinking, contractures and transverse splitting of fibres post-mortem. In fixed muscles, intracellular vacuolation, increase in intermyo-fibrillar apace, bacterial invasion and fibre disintegration ere observed. Ultrastructurnlly, the Z disk and I bands degenerate rapidly ( 4 hours), but the thick filaments of the A band are remarkably resistant to change ( 24 hours). The sarcolemma, mitochondria, snrcotubular system and ayonuclei also show marked changes in less than 4 hours. Myelin figures and autophagic vacuoles are among other features eocn in post-mortem tissue.There are more degenerate mitochondria and vesicular remnants of the sarcotubular system in the iliotibialis than the pectoral!a muscle but this reflects a differing concentration of these organelles in vivo. No other histological feature differs either in character or frequency at any time post-mortem; the variation between birds and even between fibres within the same sample is considerable.The decline in pH after death was measured in both muscles over a period of 8 hours. The pH is significantly lower in pectoralis than iliotibialis at all times post-mortem after the first five minutes.The onset of rigor mortis was studied by comparing the time to reach a 50% decrease in extensibility in the two muscles this is attained in the iliotibialis muscle in significantly less time than in pectoralis.The onset of rigor mortis was studied by comparing the time to reach a 50% decrease in extensibility in the two muscles this is attained in the iliotibialis muscle in significantly less time than in pectoralis.A study of the effect of various stages of processing on the muscles of broiler chickens at a commercial packing station has shown that changes in histology of the muscles occur much more rapidly than in the laboratory situation. Damage to the muscles is apparently incurred during scalding, plucking and chilling of the chicken carcasses.