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The effect of several flake densities (FD) of steam-processed sorghum grain on performance, and site and extent of nutrient digestibilities by steers fed growing and finishing diets was determined. The effectiveness of common laboratory methods of starch availability (enzymatic hydrolysis or gelatinization) to provide target specifications for quality control of steam-flaked grains was also measured. In vitro starch availability of the processed grains increased (P < .05) linearly in response to decreased FD. Flake density was more highly correlated with enzymatic measures than with percentage gelatinization (R2 = .87 to .93 vs .36). Using 140 crossbred beef steers (181 kg initial weight), feedlot performance was determined for 112 d with a growing diet (50% grain), followed by 119 d with a finishing diet (78% grain). Each FD treatment (412, 360, 309, and 257 g/L or 32, 28, 24, and 20 lb/bu) was randomly assigned to five pens of seven steers each. Intake of DM by steers decreased linearly (P < .05) as FD decreased (7 and 13%, respectively, for growing and finishing diets). Decreasing FD reduced linearly (P < .05) ADG in the finishing phase and for the entire 231-d trial. With the growing diet only, feed efficiency and estimated diet NEm and NEg responses to decreasing FD were curvilinear (P < .05), with the 360 g/L (28 lb/bu) flake being most efficient. Electrical energy requirements for processing increased linearly (P < .05) as FD decreased. Using four multi-cannulated crossbred steers (275 kg), starch digestibility increased linearly (P < .05) in the rumen (82 to 91%) and total tract (98.2 to 99.2%) as FD decreased. Digestibilities within the small (74%) and large intestines (62%) were not altered by FD. Decreasing FD increased (P < .05) total CP digestibility, but did not consistently alter fiber digestibility or DE content of the diets. In conclusion, enzymatic laboratory methods to evaluate starch availability in processed grains can be used satisfactorily to establish FD criteria for quality control of the steam-flaking process. The greatest improvements in efficiency, estimated diet NE, and starch and protein digestibilities usually occurred when FD was decreased from 412 to 360 g/L (32 to 28 lb/bu). Based on these measures and processing costs, the optimal FD was 360 g/L (28 lb/bu).

The objective of these two feeding trials was to determine the associative effects of feeding steam-flaked grain sorghum (SFGS) in combination with steam-flaked (SFC), dry-rolled (DRC), or high-moisture (HMC) corn on growth performance and carcass characteristics in feedlot cattle. In Trial 1, 200 yearling heifers were blocked by weight, allotted to 25 pens, and fed one of five finishing diets (77% grain, 15% corn silage, and 8% supplement on a DM basis) for an average of 137 d. The grain combinations were 100:0, 75:25, 50:50, 25:75, and 0:100 SFC:SFGS, respectively. Treatment had no effect on DMI (P > .05), but ADG, gain efficiency, and final live and hot carcass weights decreased linearly (P < .05) as the proportion of SFGS increased in the diet. Carcass backfat, quality grade, and liver abscess score were not affected (P > .05) by treatment. In Trial 2, 306 yearling steers were blocked by weight, allotted to 30 pens, and fed diets that contained 74.5% grain, 10% corn silage, 7.5% soybean meal, 4% tallow, and 4% supplement (DM basis) for an average of 139 d. The grain and grain combinations were 100% DRC, HMC, SFC, or SFGS and a 67%:33% combination of SFGS: DRC or SFGS:HMC. For steers fed diets containing a single source of grain, those fed SFC gained 7% more live weight and had a 7% higher gain efficiency (P < .05) than those fed DRC or HMC. Growth performance of steers fed SFGS was intermediate. Feeding grain combinations (67% SFGS:33% HMC or DRC) resulted in a 5 to 6% positive associative effect (P < .05) for ADG and gain efficiency. Carcass characteristics were not affected (P > .05) by treatment. We concluded that there were significant benefits (positive associative effects) when SFGS was fed in combination with DRC or HMC, but the effects were smaller when SFGS was fed in combination with SFC.

We conducted two trials to examine the effects of restricted vs full feeding and of grain processing method on feedlot performance, digestion, and mastication efficiency by Holstein steers in different growing-finishing systems. In Trial 1, 272 Holstein steers (177 +/- 9.98 kg) were blocked by weight and assigned to growing phase diets based on corn silage (SIL), steam-flaked corn that was either limit-fed (SFLF) or full-fed (SFFF), or whole corn that was limit-fed (WCLF) or full-fed (WCFF). Limit-fed steers were fed at levels predicted to allow daily gain of 1 kg/d. On d 112, all steers were switched to WCFF or SFFF diets until the mean BW of each treatment group was 545 kg. Overall, steers fed WCLF and SFLF during the growing phase and finished on SF were 8.1 and 6.6% more efficient at converting dietary ME to gain (P = .02 and .04, respectively) than steers in the SFFF group. In Trial 2, three ruminally and duodenally cannulated Holstein steers were fed whole (WC) and rolled corn (RC) diets at FF and LF intake in an incomplete replicated 2 x 2 switchback design. Ad libitum access to feed resulted in higher (P = .02) ruminal starch digestibility than did limit-feeding, and calves had higher total tract DM (P = .05) and starch (P = .03) digestion at the heavier BW. Limit-feeding whole corn resulted in increased particle size of masticate (P = .06) compared with full-feeding whole corn. Because of apparent differences in mastication efficiency between limit-fed and full-fed calves, grain processing method during periods of restriction and compensatory growth may be important considerations for managing growth in systems that incorporate limit-feeding.

Two trials were conducted to determine the effects of steam-flaked sorghum 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 lb/bu). Steers fed L consumed 3.2% less DM than those fed H (linear, P < .05), resulting in 6.9% lower ADG (linear, P = .02) and 3.6% lower gain efficiency (linear, P < .15). Sorghum grain flaked to M and L had 16 and 46% greater starch gelatinization than H (measured using differential scanning calorimetry; linear, P = .002). Dressing percentage increased linearly (P < .05) with increasing flake density, but no other carcass measurements were affected by treatment. Increasing flake density increased mill production rate linearly (P < .01), resulting in the lowest energy usage per unit of flaked grain for the H treatment. Trial 2 was an acidosis challenge 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 intake 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 and 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 challenge (P = .12). There was no significant treatment effect on ruminal lactate. Flaking sorghum grain to .283 and .322 kg/L resulted in reduced intake and poorer animal performance compared with .361 kg/L (58.7% starch gelatinization), higher susceptibility to subacute acidosis, and higher costs of production.

Twenty-four Holstein cows near peak lactation were fed diets formulated to contain 30% NDF with forage NDF from chopped wheat straw or chopped alfalfa hay in proportions of 0:3, 1:2, 2:1, and 3:0 in an 8-wk trial to evaluate effects of fiber source on lactational performance. Concentrate was based on highly degradable carbohydrate in steam-flaked sorghum grain. Forage to concentrate ratio decreased from 49:51 to 28:72 when straw was substituted for alfalfa hay. Milk yield (38.4 kg/d) and DMI (23.1 kg/d) were not influenced by forage source. Milk fat percentage decreased and milk protein percentage increased linearly with increasing straw. Yields of 3.5% FCM and fat showed linear and quadratic responses, because they appeared to be reduced only on the 0:3 diet, and protein yield showed a quadratic response and was highest for the 1:2 diet. Digestibility of NDF averaged 43.5, 45.4, 40.7, and 31.2%, and acetate to propionate ratio was 3.0, 2.4, 2.2, and 1.9 with increasing dietary straw. Passage rates were not influenced by diet and averaged 9.3, 7.6, 6.1, and 4.7%/h for fluid, grain, alfalfa hay, and wheat straw, respectively. It is suggested that the ratio of forage NDF to ruminally degradable starch be maintained greater than or equal to 1:1 when diets based on low quality forage are fed to cows in early lactation.

Three duodenally cannulated, lactating Holstein cows were dosed with rare earth-labeled grain to evaluate effects of passage model, sampling site, and marker dosing time on digesta passage parameters. Cows were given ad libitum access to feed twice daily. Rare earth-labeled grain (applied by the 24-h immersion technique) was fed immediately before (Dy) or 2 h after (Yb) the morning feeding, and duodenal digesta and feces were sampled. Marker excretion curves were fit to a two-compartment, biexponential model, using curve peeling or to a series of two-compartment models, with one to six orders of gamma time-dependency in the fast compartment, using nonlinear regression. Passage estimates from the curve-peeled, biexponential model were similar to those from the best fit of the nonlinear models, which had three orders of gamma time-dependency. Ruminal passage rate of grain, averaged across models, sampling site, and dosing time, was .077/h. Estimates of time to first appearance of marker at the sampling site and mean retention times were longer (8 vs 1 h and 25 vs 17 h, respectively), but passage rates were similar, when determined from fecal compared with duodenal samples (P less than .05). Marker dosing time did not influence any of the parameters. It is concluded that both curve-peeling (linear regression) and nonlinear regression methods can be equally useful for evaluating passage kinetics of grain in dairy cows and that sampling site and time of marker dosing have little effect on passage parameter estimates.