Feedlot performance and diet digestibility of feed efficiency-ranked beef steers fed corn or roughage-based diets and finished with corn or byproduct-based diets
The objective was to determine effects of growing phase (GP) diet and feed efficiency (FE) ranking, as well as finishing phase (FP) diet, on beef steer diet digestibility and FP growth. At University of Missouri, 193 steers were fed whole-shell corn (GPC) or roughage-based (GPR) diets using GrowSafe individual feed intake system for 70-d and FE was determined. At Iowa State University, the 12 greatest (HFE) and 12 least (LFE) feed efficient steers from each GP diet (n=48; 509±7 kg) were blocked by GP diet and FE ranking into GrowSafe-equipped pens of six. Steers were fed 10 g titanium dioxide (TiO2) daily in diets similar to GP diets for 14-d, followed by 2-d fecal collection to determine GP diet DM digestibility (GPdig). Steers were then transitioned to FP corn (FPC) or byproduct-based diets (FPB), receiving FP diets for 14-d before again being fed TiO2 daily for 14-d followed by 2-d fecal collection to determine FP diet DM digestibility (FPdig). Data were analyzed using PROC MIXED of SAS. There was a tendency for greater (P = 0.07) GPdig in HFE versus LFE steers, and FPdig was greater (P < 0.05) for steers fed FPC versus FPB diets. There was no relationship between FPdig and finishing phase G:F. There was a positive correlation between G:F in GP and FP (R = 0.29; P < 0.05). A positive correlation between GPdig and FPdig (R = 0.31; P < 0.05) was driven by a strong positive correlation between GPdig and FPdig (R = 0.71, P < 0.05) in cattle grown and finished on corn diets. Compared to LFE, HFE steers had greater finishing phase G:F (P < 0.05) and tended to have greater FP final BW and ADG (P = 0.07) while DMI did not differ due to FE rank (P > 0.1). No differences in ADG, G:F or DMI (P > 0.1) during FP were noted due to GP or FP diet effects. In this study, G:F during FP was positively related to growing phase FE ranking, and FP performance was greater in steers ranked as highly FE during GP. Differences in GPdig may help explain growing phase FE ranking. The strong correlation for diet digestibility in steers grown and finished on corn diets supports the assertion that cattle FE testing should likely be conducted using the diet most similar to the environment of interest.
Keywords: Cattle, Digestibility, Feed efficiency