An objective measure of muscularity: Changes with animal growth and differences between Genetic lines of southdown sheep

A measure of muscularity, based on objective measurements, and expressed in terms of muscle depth relative to skeletal dimensions, is proposed and investigated using a simulation model. Average muscle depth is assessed as the square root of the muscle weight per unit length of a bone adjacent to the muscle. Muscularity is then defined as average muscle depth divided by bone length. Evidence based on a theoretical model, results from the literature and data from backfat selection lines of Southdown sheep is used to illustrate how muscularity defined in this way changes with growth, and the extent to which it parallels changes in muscle to bone ratio. It is concluded that although these two characteristics often change together there are situations where differences in muscularity are not accompanied by differences in muscle to bone ratio and vice versa.