[The adaptation of histometry and immunohistochemical detection of fetal myosin as diagnostic methods for stress myopathy in swine].

The aim of this study was to examine the reliability of histometric and immunocytochemical methods in the diagnosis of stress-induced myopathies in pigs. A total of 33 German Landrace and Mangalitza pigs ranging in age from 4 weeks to 1.5 years were used for the determination of creatine kinase (CK) activity in blood serum and the histological, histometrical and immunocytochemical examination of 10 different skeletal muscles. The results show that a computer-aided histometric analysis of skeletal muscle fibers with special regard to their coefficient of variation and the interquartile range is not valuable for the diagnosis of myopathy in pigs. This contradicts the results reported in other species, where the grade of myopathy was found to correlate positively with the coefficient of variation. Using an antibody against fetal skeletomuscular myosin in immunocytochemistry, an age-dependently varying mixture of small myofibers of a physiological tapered and a pathological regenerating type was observed in porcine muscles, resulting in a relatively constant coefficient of variation of between 30-40% in skeletal muscles over the entire age range examined. In healthy porcine skeletal muscles, fetal myosin is only expressed prenatally. Thereafter, it is reexpressed only from the age of 16 weeks on and exclusively in cases of stress-induced myopathy. Therefore, the still controversial existence of a postnatal hyperplasia of skeletal muscle fibers in pigs must be rejected. The immunocytochemical detection of fetal myosin in skeletal muscles of adult pigs is the first reliable and sensitive method for diagnosis of stress-induced myopathy in pigs including latent forms of the disease.