EFFECT OF STEAM-FLAKED SORGHUM GRAIN DENSITY ON PERFORMANCE, MILL PRODUCTION-RATE, AND SUBACUTE ACIDOSIS IN FEEDLOT STEERS

Two trials were conducted to determine the effects of steam-flaked sor ghum grain bulk density on animal performance, cost of production, and propensity to induce ruminal acidosis in feedlot steers. In Trial 1, 336 yearling steers (343 kg; SEM = .346) were fed diets for 125 d that contained sorghum grain (82.5%, DM basis) flaked to .283 (L),.322 (M) , or .361 (H) kg/L (i.e., 22, 25, and 28 Ib/bu). Steers fed L consumed 3.2% less DM than those fed H (linear, P < .05), resulting in 6.9% lo wer ADG (linear, P = .02) and 3.6% lower gain efficiency (linear, P < .15). Sorghum grain flaked to M and L had 16 and 4 6% greater starch g elatinization than H (measured using differential scanning calorimetry ; linear, P= .002). Dressing percentage increased linearly (P < .05) w ith increasing flake density, but no other carcass measurements were a ffected by treatment. Increasing flake density increased mill producti on rate linearly (P < .01), resulting in the lowest energy usage per u nit of flaked grain for the H treatment. Trial 2 was an acidosis chall enge study that incorporated six ruminally cannulated steers (422 kg; SEM = .129) into a replicated 3 x 3 Latin square experiment, Reducing flake density resulted in linear reductions in ruminal pH following in take challenge at 3, 33, and 36 h after the d-12 challenge (P < .05). There was a linear increase in the area between the pH vs time curve a nd a line at pH 5.5 (P < .01) and 5.0 (P = .09) with decreasing flake density (28.0, 25.2, and 18.2 pH-hours below 5.5 and 9.6, 7.3, and 3.9 pH-hours below 5.0 for L, M, and H, respectively). Cattle consuming L also tended to have higher VFA concentrations (mM) at 36 h after chal lenge (P = .12). There was no significant treatment effect on ruminal lactate. Flaking sorghum grain to .283 and .322 kg/L resulted in reduc ed intake and poorer animal performance compared with .361 kg/L (58.7% starch gelatinization), higher susceptibility to subacute acidosis, a nd higher costs of production.