The chemical composition of the muscle and fatty carcass tissues of Hereford × Friesian (HE), Friesian (FR) and Charolais × Friesian (CH) steers finished on high (H) (12·6 MJ/kg dry matter) and medium (M) (10·4 MJ/kg dry matter) metabolizable energy (ME) concentration diets and slaughtered at low (L), normal (N) and heavy (W) carcass weights was determined in a 3 × 2 × 3 (no. = 9) factorial experiment. There were also pre-finishing slaughter groups of nine animals of each breed type. Target L, N and W carcass weights were 260, 300 and 340 kg, for HE and FR and 260, 320 and 380 kg, for CH, respectively.
Main effect side soft tissue weights of the finished groups were 128, 125 and 134 (s.e.d. 1·3) kg for HE, FR and CH, 133 and 125 (s.e.d. 1·1) kg for H and M and 108, 129 and 150 (s.e.d. 1·3) kg for L, N and W, respectively. Soft tissue chemical composition was 540, 562 and 590 (s.e.d. 5·0) g/kg moisture, 162, 174 and 181 (s.e.d. 1·7) g/kg protein and 288, 254 and 220 (s.e.d. 6·6) g/kg lipid for HE, FR and CH and 558 and 570 (s.e.d. 4·1) g/kg moisture, 170 and 175 (s.e.d. 1·4) g/kg protein and 262 and 246 (s.e.d. 5·4) g/kg lipid for H and M, respectively. The allometric regression coefficients for moisture, protein and lipid weights on soft tissue weight were 0·65, 0·69 and 206, respectively. The coefficients for moisture and protein weights on muscle and fat weights were < 1·0, whereas for lipid, they were >1·0. The breed differences in soft tissue chemical composition paralleled differences in physical composition. Dietary ME concentration had little effect on the chemical composition of individual tissues. For the M diet, HE, FR and CH were calculated to have similar soft tissue lipid concentrations (250 g/kg) at side soft tissue weights of 113, 125 and 157 kg, respectively. Corresponding side muscle weights at similar muscle lipid concentration (70 g/kg) would be 77, 90 and 108 kg.