Relationships between beef carcass shape and muscle to bone ratio

Relationships between muscularity and muscle to bone ratio were investigated for beef carcasses of several breeds and crosses, and three genders using data from Bristol and Alberta. Side dissection data in terms of muscle, fat and bone weights were used to calculate muscle to bone ratios (MtoB) and muscularity indexes (MUSC) for the whole side or for the region around the femur bone. Highly significant breed and gender effects on MtoB and MUSC were shown for both the Bristol and the Alberta data sets, but the group differences for MtoB were not the same as those for MUSC despite the fact that these two characteristics were closely correlated. For both sets of data, for example, MUSC values at a common muscle plus bone weight were significantly higher for carcasses of bulls than heifers, but similarly adjusted MtoB values were generally higher for carcasses of heifers than bulls. Differences among breed groups were mainly in a similar direction for MUSC and MtoB, but the size of the differences varied widely. For example, relative to the Friesian, the Jersey breed had a significantly higher MtoB but a significantly lower MUSC, and carcasses of double-muscled bulls had a femur-region MtoB that was 19.2% greater than that of a group of Shorthorn-cross carcasses, but a MUSC that was only 1.7% higher. These findings show that because of the inconsistent relationships between muscularity and muscle to bone ratio among different classes of beef carcasses, lean meat yield cannot always be predicted without bias if measures of carcass shape are used as indicators of muscle to bone ratio.