Flake density of steam-processed sorghum grain alters performance and sites of digestibility by growing-finishing steers

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 gelatin ization) to provide target specifications for quality control of steam-flak ed grains was also measured. In vitro starch availability of the processed grains increased (P < .05) linearly in response to decreased FD. Flake dens ity was more highly correlated with enzymatic measures than with percentage gelatinization (R-2 = .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% gr ain). Each FD treatment (412, 360, 309, and 257 g/L or 32, 28, 24, and 20 l b/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%, respect ively, 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 g rowing 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) fl ake being most efficient. Electrical energy requirements for processing inc reased linearly (P < .05) as FD decreased. Using four multicannulated cross bred steers (275 kg), starch digestibility increased linearly(P < .05) in t he rumen (82 to 91%) and total tract (98.2 to 99.2%) as FD decreased. Diges tibilities within the small (74%) and large intestines (62%) were not alter ed 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 q uality control of the steam-flaking process. The greatest improvements in e fficiency, estimated diet NE, and starch and protein digestibilities usuall y occurred when FD was decreased from 412 to 360 g/L (32 to 28 lb/bu). Base d on these measures and processing costs, the optimal FD was 360 g/L (28 lb /bu).