One hundred and twenty spring-born steers comprising 40 Friesians (FR), 40 Limousin × Friesians (LM), and 40 Blonde d'Aquitaine ' Friesians (BL), were reared together from shortly after birth to slaughter at a mean age of 771 days. They were at pasture in summer and were housed and offered grass silage plus concentrates in winter. All were implanted with anabolic agents. During the finishing winter, there was a 3 (breed types) ' 2 (3 or 6 kg concentrates per day) ' 2 (94 or 181 day finishing period) factorial arrangement of treatments.
Slaughter weights per day of age, carcass weights per day of age and carcass weights of FR, LM and BL were 846, 828 and 866 (s.e. 8·0) g, 464, 476 and 497 (s.e. 4·9) g and 358, 368 and 385 (s.e. 3·8) kg respectively. LM had lower carcass length, carcass depth, leg length and leg width values than FR or BL but when these measurements were expressed per kg carcass weight the values for LM and BL were similar. Both LM and BL had better carcass conformation than FR, and BL had a lower carcass fat score than either FR or LM between which there was no difference. FR, LM and BL had carcass lean, fat and higher-priced lean proportions of 634, 669 and 685 (s.e. 3·7), 185, 168 and 144 (s.e. 3·7) and 352, 361 and 361 (s.e. 1·4) g/kg respectively.
Increasing the concentrate level from 3 to 6 kg per day increased side weight by 9·6 kg (P < 0·001). This consisted of 0·6 kg bone, 3·3 kg lean and 5·7 kg fat. Extending the finishing period from 94 to 181 days increased side weight by 30·3 kg (P < 0·001). This consisted of 2·6 kg bone, 12·0 kg lean and 15·7 kg fat. Allometric regression coefficients for side lean, bone and fat weights on side weight were not significantly affected by breed type or concentrate level. The coefficients for lean, bone and fat were 0·80 (s.e. 0·04), 0·58 (s.e. 0·05) and 2·27 (s.e. 0·16) respectively. The coefficients for weights of lean in the hind-shin, fore-shin, fillet and brisket on side lean weight were 0·8 or lower. The corresponding coefficients for silverside, inside round, knuckle, rump and strip-loin were between 0·8 and 1·0 while the flank, shoulder, neck, chuck, plate, fore-rib and cube-roll had coefficients in the range 1·0 to 1·5.