Skeletal muscle fibre characteristics in young and old bulls and metabolicresponse after a bullfight

Fibre type composition, activities of enzymes such as citrate synthase (CS) , 3-hydroxyacyl coenzyme A dehydrogenase (HAD), lactate dehydrogenase (LDH) , as well as glycogen, lactate and pH levels were analysed in muscle biopsi es (m. gluteus medius) obtained after bullfighting from 10 young and 10 old bulls. No changes were seen in fibre type composition between groups, but the older bulls had higher HAD and LDH activities. Low glycogen concentrati ons and low pH values were found in both groups, but the lactate concentrat ion after bullfighting was higher in the older group of bulls. The histoche mical stain for glycogen revealed that type IIB fibres in both young and ol d bulls contained more glycogen than seen in type IIA and type I fibres. Th ese results show that young and old bulls have similar muscle fibre type co mposition, but the metabolic capacity differs, with a higher glycolytic cap acity and lactate production in older bulls. Furthermore, it seems that the physical and emotional stress in connection with a bullfight causes a mark ed depletion of glycogen, especially of type I and IIA fibres.