Observations on the Postmortem Histochemistry of Myofibers from Stress Susceptible Pigs 1,2

Postmortem myofiber histochemistry was studied in longissimus muscles of pigs with differing degrees of stress susceptibility (SS). The histochemical reactivity of phosphorylase and the stainability of glycogen by the periodic acid-Schiff (PAS) reaction was enhanced in samples taken approximately 20 min. postmortem. In later postmortem samples from SS animals killed by stress treatment, phosphorylase and PAS reactions were lost in all except some red myofibers. Of 12 SS animals examined, seven had a high proportion of white myofibers, three had a high proportion of intermediate type myofibers and two had myofibers with a high glycogen content but no demonstrable phosphorylase activity. Extremely SS animals had more myofibers with a positive PAS reaction than moderately SS animals.