Experimental Procedures
The trial began on 1/27/00. The trial was a 2 X 2 factorial investigating two corn types and two processing methods. One hundred sixty steers were allotted to 20 pens. Pens (15 X 15 feet) were constructed of metal gates and cable, had slatted floors, and were located in an open-sided barn. There were 22 inches of bunk space per steer. Each pen had the same approximate average starting weight (774 lb). Cattle were weighed on two consecutive days initially and at the termination of the trial, and every 28 days during the trial. A two week adjustment period using three transition rations was used to adjust cattle to their finishing rations. Final diets were 73% corn, 12% corn silage, and 15% supplement (on a dry matter basis). Diet composition is in Table 1.
Feed was delivered once daily beginning at 0900 hours. Daily feed offered and weighbacks were recorded. On a dry matter basis, diets were formulated to contain 13.7% CP, 27 g Rumensin/ton, 10 g of Tylan/ton, 0.63% Ca and 0.36% P. Feedstuffs were analyzed weekly for DM and feed samples were composited and analyzed for protein and fiber every 28 days. Steers were implanted with Synovex-S 70 days before the trial began and were reimplanted with Revalor-S on day 28 of the trial. The trial was terminated on day 133.
High oil corn (purchased courtesy of Optimum Quality Grains, Des Moines, IA) was obtained from a Central Ohio grain farmer. This corn and "normal" corn (grown by OSU) was fed either whole or was rolled through a roller mill. Median particle size for both corn types was approximately 0.1 inch. Particle size distributions for rolled corn of both types is shown in Figure 1.
On day 56, fecal grab samples were collected (during weighing; before feeding) from three steers per pen. Half of the composited fecal sample from each pen was dried and analyzed for N and acid-ether extract. Apparent digestibility of ether extract was determined using CP as a marker (NRC, 1985). Digestible protein was calculated by: 0.9 (% dietary CP) - 3. Indigestible CP and fecal CP concentrations were used to determine fecal DM output.
The trial was terminated when cattle were judged to be approximately 80% choice (based on visual appraisal). Cattle were slaughtered by Moyer Packing Co., Souderton, PA. Carcass data were collected by a trained, experienced meats specialist from Penn State University. Although 160 steers began and finished the trial, carcass data are summarized for 150 steers. Ten carcasses were deleted from the data set due to random problems associated with tracking carcasses at the packing plant (four missing carcasses that did not get graded and three sets of duplicate tag numbers; hot carcass weight (HCW) were similar between duplicates). Daily gain, DM feed intake, feed conversion, and carcass characteristics were determined. Data were analyzed using the GLM procedures of SAS. The model contained effects due to corn source, processing type and the interaction of these main effects. Pen served as the experimental unit.