Histomorphological and histochemical analysis of some skeletal muscles in fattened bulls

White fast-twitch glycolytic (FG) fibres of large diameter, red slow-twitch oxidative (SO) fibres of small diameter and intermediate fast-twitch oxida tive (FOG) glycolytic fibres of intermediate diameter were found in the sam ples of m. obliquus abdominis externus, m. Pectus abdominis, m. triceps bra chii (caput longum), m. pectoralis superficialis, m. longissimus dorsi (2 s amples), m. psoas major and m, semimembranaceus taken from both body sides of 5 fattened bulls, 15 months old and weighing 400 kg. The white fibres do minate in all muscle samples and they show a strong activity of standard (S ATP) and alkaline stable adenosine triphosphatase (AL ATP), a weak activit y of lactate and succinate dehydrogenase (LDH and SDH) and of acid stable a denosine triphosphatase (AC ATP), a low content of lipids and a high conten t of glycogen. In 4 muscles the red fibres are more numerous than the inter mediate ones. They show a strong activity of LDH and SDH, of AC ATP, a weak activity of S ATP and AL ATP, a high content of lipids and a low content o f glycogen. The FOG fibres are more numerous than the SO ones in 3 muscles (4 samples), and they show a strong activity of S ATP and AL ATP, a weak ac tivity of AC ATP, a moderate activity of LDH and SDH as well as a varying c ontent of lipids and glycogen. The muscle fibre diameters ranged from 20 to 115 mum, but the largest average diameter was found in m, psoas major, the smallest being in m. obliquus abdominis externus. The differences in muscl e fibre diameters between the left and the right side of the body were not significant (P > 0.05).