Influence of Breed Type, Sex, Feeding Systems, and Muscle Bundle Size on Bovine Fiber Type Characteristics

Fiber type numbers, percentages and diameter were evaluated in two experiments. Experiment 1 contained Angus and Angus cross cattle consisting of 48 steers and 48 heifers with half of each sex fed grain while the other half were fed grain-on-grass. Experiment 2 contained 12 Angus and 12 Simmental cross steers slaughtered at four feeding system endpoints. Steers tended to have a higher percentage of βR and a lower percentage of αW fibers than heifers; The percentage of βR fibers increased in the longissimus and semi-membranosus, while the αW fibers decreased. The percentage of αW fibers in the biceps femoris and semitendinosus muscles increased over the longer feeding period while the percentage βR tended to decrease. Breed appeared to have little effect on histological traits in the longissimus and semimembranosus muscles. Bundle size had no effect on fiber type diameter; however, in all muscles there was a tendency for the βR population to increase as bundle size increased.