Influence of Genotype and Diet on the Chraracteristics of Semitendinosus Muscle in Crossbreed Young Bulls derived from Brown Swiss Cow and Double Muscled Bulls

The aim of this study was to evaluate the influence of genotype and diet on the characteristics of muscle fibers and adipocytes of the semitendinosus muscle in crossbred young bulls derived from Brown Swiss cows (B) and double-muscled Piemontese (PI) or Belgian Blue (BB) bulls. For this purpose 24 young bulls divided in 6 groups fed 3 diets have been used: a control diet without supplementation of rumen protected CLA (rpCLA), and two other diets added with 8 or 80 g/d of a supplement of rpCLA. The histochemical methods (succinic dehydrogenase and mATPase) pointed out the presence of three fiber types: type I, type IIA and type IIX. Results demonstrated that genotype affected both fiber type number and size. While there was no significant difference among the percentages of type I fibers (PI×B 12.73%, BB×B 12.95%), the difference was significant (P<0.05) for IIA fiber type (PI×B 23.03%, BB×B 29.13%) and for IIX fiber type (PI×B 64.53%, BB×B 57.84%). All the fiber types of the BB×B genotype had a significantly bigger size (P<0.05) than the fibers of PI×B genotype. The adipocytes analyses showed a significant effect (P<0.05) of genotype on the adipocytes total surface. The level of CLA addition did not affected neither muscle fiber nor adipocytes characteristics.