Influence of flake thickness on the feeding value of steam-rolled wheat for feedlot cattle

Seventy-two medium-framed, crossbred steers (348 kg) were used in a randomized complete block design performance trial. Experimental diets contained (DM basis) 6% alfalfa hay, 6% sudangrass hay, 79% wheat, 2% yellow grease, 4% cane molasses, and 3% supplement. Treatments were 1) dry-rolled wheat (DRW, density = .52 kg/L); 2) steam-rolled wheat, coarse flake (SRW-C, density = .39 kg/L); and 3) steam-rolled wheat, thin flake (SRW-T density = .30 kg/L). Steam processing increased amyloglucosidase reactivity of wheat starch by 238 and 287% for SRW-C and SRW-T, respectively. Cattle performance was similar (P > .10) for SRW-C and SRW-T. Steam processing wheat increased ADG (13.5%, P < .10) and decreased DM intake/gain (8.8%, P < .05). Diet NE was precisely as expected for DRW, confirming the applicability of tabular NE values. Diet NEm, was 3.7% lower (P < .05) for DRW than for SRW. The NEm and NEg of SRW were 2.28 and 1.59 Mcal/kg, respectively. Twelve Holstein steers (266 kg) were "T" cannulas in the rumen and proximal duodenum were used in a completely random design experiment to evaluate treatment effects on characteristics of ruminal and total tract digestion. Ruminal digestibilities of OM and starch were similar (P > .10) for DRW and SRW. Postruminal and total tract digestibility of OM (P < .10) and starch (P < .01) were increased with SRW. Dietary DE and ME values were greater (6.1 and 6.6%, respectively; P < .10) for SRW than for DRW. The DE and ME values for SRW were 4.13 and 3.41 Mcal/kg, respectively. Ruminal degradation of feed N was decreased (27%, P < .05) and postruminal N absorption increased (11%, P < .05) with SRW. The advantages of SRW compared with DRW include 1) enhanced energy intake and ADG, 2) improved feed efficiency, 3) increased NE value, and 4) increased ruminal escape and postruminal absorption of feed N. There is no apparent benefit to decreasing the thickness of SRW to < 1.35 mm.