The effect of feed efficiency classification on visceral organ mass in finishing steers

Individual feed intake of crossbred beef steers (one contemporary group/year, 2 years) was recorded during finishing to investigate visceral organ mass in steers divergent for feed efficiency. Based on residual feed intake (RFI), the 20% most efficient (HE, n = 8/year) and 20% least efficient (LE; n = 8/year) steers with 12th rib fat >1.02 cm were slaughtered. High efficiency steers had less DM intake (P < 0.001), greater G:F (P < 0.001), and similar ADG and hot carcass weight (HCW). High efficiency steers tended to have less (P < 0.10) small intestinal mass (actual and relative to BW and HCW) in year 1. In year 2, HE steers tended to have greater (P < 0.10) large intestinal actual and relative masses. Low efficiency steers tended to have greater (P = 0.06) actual omasum mass and had greater (P < 0.03) relative omasum masses compared with HE. Stomach complex, total gastrointestinal tract, liver, and kidney masses tended to be greater (P < 0.10) relative to BW, and were greater (P < 0.05) relative to HCW, in LE. Data suggest that visceral organ mass, especially of the gastrointestinal tract, plays a role in overall metabolic efficiency of finishing steers.