Changes in muscularity with growth and its relationship with other carcass traits in three terminal sire breeds of sheep

Data were available for 160 sheep (50 Suffolk males, 50 Suffolk females, 40 Texel males and 20 Charollais males). One-fifth of animals within each breed and sex were slaughtered at each of 14, 18 or 22 weeks of age and two-fifths slaughtered at 26 weeks. After slaughter linear measurements were taken on the carcass. The left side of each carcass was then separated into eight joints and each joint dissected into lean, bone and fat. Five muscularity measures (three for the longissimus thoracis et lumborum (LTL) muscle, one for the hind leg and one for the whole carcass) and one of the shape of the LTL cross-section (depth : width) were calculated. With the exception of one measure for the LTL, muscularity increased with growth. Rates of increase in most measures were higher in Texels than in each of the other breeds, but were not different between the male and female Suffolks or between the Suffolk and Charollais lambs. Increases in most muscularity measures at a constant live weight were associated with increases in lean to bone ratio and carcass lean content. Associations with fat content were either non-significant or negative. Relationships with lean distribution were non-significant or weak. Correlations between the three measures of muscularity for the LTL were high. Correlations between the whole carcass measure and those within different regions were moderate to high in the Texels but lower in the Suffolk and Charollais breeds. The same was true for correlations between the LTL measures and hind leg muscularity. If muscularity throughout the carcass is to be described effectively, measures in more than one region may be required, particularly in the Suffolk and Charollais breeds.