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Influence of growing phase feed efficiency classification on finishing phase growth performance and carcass characteristics of beef steers fed different diet types
A multi-year study utilized 985 crossbred steers (464 ± 32 kg, SD) fed in six separate groups to determine the influence of growing phase (GP) feed efficiency (FE) classification and diet type on finishing phase (FP) FE. At University of Missouri, steers were fed GP corn (G-Corn; 528 steers) or roughage-based (G-Rough; 457 steers) diets using GrowSafe feed bunks to measure DMI for 69-89 d. At the end of the GP, steers were ranked by residual feed intake (RFI), shipped to Iowa State University, and blocked into FP pens (5-6 steers/pen) by GP diet and RFI rank (lower, middle, or upper one-third). Steers were transitioned to either FP corn or byproduct-based diets. After completion of the sixth group, average GP gain:feed within GP diet was calculated for each FP pen (168 total pens) using GP initial BW as a covariate. Pens were classified as highly (HFE; > 0.5 SD from the G:F mean; 58 pens), mid (MFE; ± 0.5 SD from the G:F mean; 60 pens), or lowly (LFE; < 0.5 SD from the G:F mean; 50 pens) feed efficient. Data were analyzed using PROC MIXED of SAS. Experimental unit was FP pen and the model included the fixed effects of GP diet, FE classification, FP diet, and the interactions. Group (1-6) was included as a fixed effect. There were no three-way interactions (P ≥ 0.2) for any traits. Finishing phase G:F was not affected by any interactions (P ≥ 0.5) but was greater (P ≤ 0.03) for HFE versus MFE and LFE and greater (P = 0.02) for MFE versus LFE. Growing phase diet × FE classification effects were detected (P ≤ 0.01) for FP final BW (FBW), ADG, and DMI. Among G-Corn steers, LFE had greater (P = 0.03) FBW than HFE while ADG was unaffected (P ≥ 0.2) by FE classification but among G-Rough steers, HFE and MFE had greater (P ≤ 0.04) FBW and ADG than LFE. Among G-Corn steers, LFE had greater (P ≤ 0.003) DMI than MFE and HFE but DMI was unaffected (P ≥ 0.3) by FE classification among G-Rough steers. Overall, differences in finishing phase G:F between FE classifications were driven by different factors depending on diet; DMI differed among corn-grown steers and ADG differed among roughage-grown steers. In this study, FE was repeatable from the growing to the finishing phase.
Keywords:
Cattle, Feed efficiency, Repeatability