Results
Diet means for steer performance are presented in Table 2. The trial was 133 days and steers started with an initial bodweight (BW) of 774 lb. Daily rate of gain was not affected (P = 0.27) by dietary treatment. Daily DM intake was greater (P < 0.01) for steers fed the rolled normal corn diet than those fed the other three diets. This response is somewhat surprising; processing increased intake of normal corn diets but not high oil corn diets (type × processing interaction, P = 0.07; Table 3). The main effect of corn types on feed conversion was significant (P < 0.06); Table 3). Improved feed conversion for high oil corn diets likely reflects their higher energy content. Digestibility of acid ether extract was estimated on fecal grab samples utilizing N as a marker to determine fecal output. The rolled normal corn diet had higher (P < 0.02) ether extract digestibility than the whole normal corn diet and both of the oil corn diets. Cautious interpretation of this digestibility value is warranted. This trial was not designed to determine digestibilities accurately and a more comprehensive investigation of digestibility may be revealing.
Treatment means and main effects on carcass characteristics are presented in Tables 4 and 5, respectively. There was an interaction of corn type and processing for hot carcass wt (P < 0.04; Table 5). Rolling normal corn increased carcass wt while rolling high oil corn tended to decrease carcass weight. Dressing percentage, marbling score, and USDA Quality were not affected (P > 0.10) by corn type or processing. Steers fed whole normal corn had less backfat than those fed rolled normal corn while processing high oil corn did not affect backfat (interaction; P < 0.07; Table 5). Internal fat (% KHP), ribeye area, and USDA yield grade were not affected (P > 0.10) by diet. Steers fed normal whole corn had the greatest (P < 0.03) percentage of Yield Grade 1 carcasses, but the percentage of Yield Grade 4 and 5 carcasses were not affected (P > 0.51) by dietary treatment. As was planned, about 80% of the carcasses from cattle in this trial graded Choice. The percentage of carcasses grading low choice and above was not affected (P < 0.40) by corn type or processing. Cattle fed high oil rolled corn had the lowest percentage of carcasses grading average choice or above; whole and rolled normal corn was highest and whole high oil corn was intermediate.
Corn particles recovered in fecal grab samples were characterized and results are presented in Table 6. It must be pointed out that the values presented are concentrations of corn in the fecal DM and do not represent total fecal output. Whole corn kernels represented about 9% of fecal DM for both normal corn and high oil corn. For all diet combinations, recoverable corn represented about 20% of fecal DM. Based on particle size distribution due to rolling (Figure 1) and corn recovered in feces, it seems there are not meaningful differences in the physical characteristics of normal and high oil corn. The ether extract (EE) content of fecal-recovered corn reflects the differences in ether extract content of these two corn sources before feeding (4.47% EE for normal corn and 8.21% EE for high oil corn). Ether extract concentration of fecal corn would be affected by digestibility of non-lipid components as well as the lipid fraction.
In summary, processing high oil corn did not improve intake, feed efficiency or carcass characteristics. The main effect of corn type revealed that high oil corn did not affect gain but resulted in slight reductions in intake, improved feed conversion, and slightly higher average Yield Grade versus normal corn. Corn type did not affect percentage of Yield grade 4 or 5 carcasses.