SUMMARY

Growth, feed intake, feed efficiency and carcass traits on 208 yearling Angus steers differing in genetic merit for residual feed intake (RFI) were measured in a large commercial feedlot. At feedlot entry the steers were drafted into three groups: high efficiency (HE; midparent RFI-EBV ≤-0.3kg/day, medium efficiency (ME: midparent RFI-EBV>-0.3 to 0.14 kg/day), and low efficiency (LE; midparent RFI-EBV ≥0.16 kg/day), and feedlot performance evaluated over 251 days. Whilst individual animal weight and carcass data were collected, daily feed consumption was recorded on a group basis. The HE steers grew as fast or faster than either the ME and LE steers (1.11 ±0.02 (sd) v 1.06 ±0.01 and 1.07 ±0.02kg/day). At slaughter the HE and ME groups were heavier than the LE group (713 ±5 and 714 ±5 v 701 ±5 kg). The HE steers consumed less feed than the ME and LE steers over the 251 days (10.4 v 11.8 and 11.1kg/day). Compared to the LE steers, the HE steers had a 10 % lower FCR and 0.98kg/day lower RFI. Carcass weight and dressing percentage were lowest in the LE steers, and eye muscle area was highest in the ME steers. Subcutaneous rib fat depth on the carcass was lower in the HE steers than for the ME and LE steers (15.6 ±0.6 v 17.6 ±0.6 and 20.7 ±0.6mm). AUSMEAT and USDA marbling scores were highest in the ME group and not different for the HE and LE groups. The experiment showed that genetic superiority in RFI reduced feed consumed over 251 days of feeding in a large commercial feedlot with no compromise in weight gain, carcass weight, dressing percentage or marbling grade