The experiment was carried out on 29 hybrids (21 barrows and 8 gilts) of Duroc sows with wild boar (Sus scrofa ferus L.). All the animals were fed (ad libitum with composed fix) from weaning up to the age of approx. 8 months. The samples of Longissimus lumborum for histopathological study were collected 45 min after slaughter and were frozen with liquid nitrogen. Microscopic preparations were stained according to the Van Gieson method. The following types of histopathological changes were accounted for: changes in fibre size (fibre atrophy, hypertrophy – giant fibres), changes in fibre shape (triangular, trapezoid and elongated fibres), degenerative changes of fibres (necrosis plus phagocytosis, fibre splitting) and connective tissue hypertrophy. Most often appearing pathological change in the muscle was fiber atrophy. It was observed in all animals. The other changes appeared with greater frequency in gilts. Percentage of particular pathological changes was low, 95.84% of normal fibers were found.