Influence of feed efficiency ranking on diet digestibility and performance of beef steers

Abstract Text:

The study objective was to determine effects of growing phase (GP) diet, GP feed efficiency (FE), and finishing phase (FP) diet on diet digestibility and FP feed efficiency. Two groups, totaling 373 steers, were fed at the University of Missouri (70-d GP), shipped to Iowa State University (ISU) for finishing, and fed in GrowSafe bunks during both phases. During GP, steers received whole shell corn (GCorn) or roughage-based (GRough) diets. Within each group, the 12 greatest and 12 least feed efficient steers from each GP diet (n = 96 total; 488±5 kg) were selected. At ISU, steers were fed 10 g titanium dioxide (TiO₂) daily in receiving diets similar to GP diets for 14-d, followed by 2-d fecal collection to determine diet DM digestibility during GP (GDMdig). For FP, steers were transitioned to corn (FCorn) or byproduct-based diets (FByp). Optaflexx was fed for 28-d prior to harvest and the TiO₂ protocol was repeated immediately before Optaflexx introduction to determine FP diet digestibility (FDMdig). The 96 steers were ranked by growing phase G:F and categorized as the 24 greatest (HFE) or 24 least (LFE) feed efficient steers from each GP diet. Data were analyzed using PROC MIXED of SAS with group as a random effect. The HFE steers tended to have greater GDMdig than LFE (69.1% vs 65.5%; P = 0.13), but FDMdig did not differ due to FE (P = 0.9). A positive correlation between GDMdig and FDMdig (R = 0.39, P < 0.01) was driven by positive correlations for digestibility between feeding phases in GCorn-FCorn steers (R = 0.49, P = 0.02) and GRough-FByp steers (R = 0.68, P < 0.01). Despite greater finishing G:F in HFE versus LFE steers (P = 0.04),  there was no correlation for overall G:F between phases (P = 0.2) and a negative correlation for G:F between phases in GRough-FCorn steers (R = -0.57, P < 0.01). Growing phase G:F and digestibility tended to be positively correlated (R = 0.2, P = 0.07); however, finishing G:F and digestibility were negatively correlated (R = -0.35, P < 0.01). In this study, digestibility was positively correlated between feeding phases when steers were grown and finished on similar diets. Feed efficiency was negatively correlated between phases when steers were roughage-grown and corn-finished, reinforcing the idea that cattle should be FE tested using diets similar to the production environment of interest.

Keywords:

Cattle, Digestibility, Feed efficiency