Infl uence of Genotype and Diet on the Characteristics of Semitendinosus Muscle in Crossbred Young Bulls Derived from Brown Swiss Cow and Double Muscled Bulls

Th e aim of this study was to evaluate the infl uence of genotype and diet on the characteristics of muscle fi bers 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), two other diets added with 8 or 80 g/d of a supplement of rpCLA. Th e histochemical methods (succinic dehydrogenase and mATPase) pointed out the presence of three fi ber types: type I, type IIA and type IIX. Results demonstrated that genotype aff ected both fi ber type number and size. While there was no signifi cant diff erence among the percentages of type I fi bers (PI×B 12.73%, BB×B 12.95%), the diff erence was signifi cant (P<0.05) for IIA fi ber type (PI×B 23.03%, BB×B 29.13%) and for IIX fi ber type (PI×B 64.53%, BB×B 57.84%). All the fi ber types of the BB×B genotype had a signifi cantly bigger size (P<0.05) than the fi bers of PI×B genotype. Th e adipocytes analyses showed a signifi cant eff ect (P<0.05) of genotype on the adipocytes total surface. Th e level of CLA addition did not aff ected neither muscle fi ber nor adipocytes characteristics.