Histochemical, morphometrical and metabolic characteristics of the Gluteusmedius muscle from horses in training for jumping competition

Biopsies were taken at a depth of 3 and 6 cm from the Gluteus medius muscle of 7 mares and 3 castrated male horses. The animals were 4 years aid and s ubmitted to a previous specific training program for jumping during 6 month s. The samples were analysed by the mATPase miofibrillar technique to deter mine the fibrillar composition, and by the NADH-TR technique to determine t he oxidative capacity of the fibres. In addition, the fibre metabolic activ ity was determined by enzyme activities of the citrate synthetase (CS), 3-O H-acil CoA dehydrogenase (HAD), lactic dehydrogenase (LDH) and creatinkinas e (CK). The averages obtained far the fibrillar composition were 14, 28, 41 and 17% at 3 cm depth and 25, 30, 34 and 10% at 6 cm depth for oxidative type I, I IA, IIB and non oxidative IIB fibres, respectively. The fibrillar compositi on varied in relation to the depth of the biopsy. Type 1 and type II B fibr e percentages showed significant differences between 3 and 6 cm. Type IIA f ibres were similar in percentage at both depths whilst, oxidative and non o xidative fibres type IIB showed a statistically significant difference in p ercentage of fibrillar composition at both biopsy depths. The area of the m uscle fibres at 3 cm depth was 2191; 3466 and 5578 mm(2) for fibres type I, IIA and IIB, respectively and the lesser diameters were 19; 24 and 30 for fibres type 1, IIA and IIB, respectively. The area of the fibres at 6 cm de pth was 2433; 3929 y 5558 mm(2) and the lesser diameters were 20; 25 y 30 f or fibres I, IIA and IIB, respectively. The activity of CS, HAD, LDH, and CK enzymes was 817, 243, 1.20 and 1.80 U/ mg protein at 3 cm depth and 1479, 542, 1.58 and 3.30 at 6 cm depth. The ac tivities of CS and HAD enzymes were significantly different between depths during the training period. These results show that the training produced changes in the fibrillar comp osition and metabolic capacity of the Gluteus medius in horses prepared for jumping competition. Significant differences were obtained in the fibrillar composition and enzy matic activities when comparing pre-training and post-training data.