Growth-and breed-related changes of muscle fiber characteristics in cattle

The objective of this study was to investigate the growth- and breed-relate d changes of muscle fiber characteristics in cattle and their importance to meat quality. Four cattle breeds with different growth impetus and muscula rity were reared and slaughtered under experimental conditions. German Angu s as a beef type, Galloway as a hardy type, Holstein Friesian as a dairy ty pe, and double-muscled Belgian Blue as an extreme type for muscle growth we re used. Between 5 and 17 bulls of each breed were slaughtered at 0, 2, 4, 6, 12, 18, and 24 mo of age. Muscle fiber traits were determined and classi fied by computerized image analysis, and several measures of meat quality w ere also determined, including shear force value, meat color, and i.m. fat content. The postnatal growth of semitendinosus muscle in cattle was charac terized by a nearly 10-fold increase of muscle fiber area from birth to 24 mo of age. In the first few months after birth, a transformation of type II A fibers into IIB fibers was found, whereas type I fibers were nearly unaff ected by age. The apparent total muscle fiber number of semitendinosus musc le did not increase during postnatal life. These results confirm that the f iber number is determined in embryonic development. Throughout the study, t he double-muscled Belgian Blue (BBDM) bulls had almost twice the fiber numb er of the other breeds, emphasizing a more extensive hyperplasia of muscle fibers during embryonic development in BBDM compared with the other three b reeds. The apparent number of type I fibers was, however, not affected by b reed, which suggests that the additional fibers found in BBDM postnatally w ere type IIB and IIA fibers. We did not find significant differences in mus cle fiber total number, muscle fiber type frequencies, or meat quality char acteristics among breeds, with the exception of BBDM. Having pooled the fou r breeds, paler meat was related to a higher frequency of type IIB fibers, a lower area of type IIA and type I fiber, and a higher total muscle fiber number. These findings based on data of double muscling give us some hints for biological causes for the variation of meat quality. Further investigat ion, in particular within each breed, is necessary to identify the superior fiber traits for bovine meat production.