COMPARATIVE FEEDING VALUE OF SUPPLEMENTAL FAT IN STEAM-FLAKED CORN-BASED AND STEAM-FLAKED WHEAT-BASED FINISHING DIETS FOR FEEDLOT STEERS

One hundred thirty crossbred steers (324 kg) were used in a 121-d comparative slaughter trial to evaluate the feeding value of fat in steam-flaked corn- [SFC] or wheat- [SFW] based diets. Treatments consisted of an 88% concentrate finishing diet containing 1] SFC, no fat; 2] SFC, 6% yellow grease [YG]; 3] SFC, 6% cottonseed oil soapstock [COS]; 4] SFW, no fat; 5] SFW, 6% YG; and 6] SFW, 6% COS. There were no interactions [P > .10] between grain type and performance response to supplemental fat. Fat supplementation increased [P < .05] ADG by 7.3% and decreased [P < .01] DMI/gain by 10.6%. Fat supplementation decreased [P < .05] ruminal OM digestion by 5% and net flow of microbial N to the small intestine by 14.5% but did not affect [P > .10] total tract digestion of OM, ADF, or starch. Substituting SFW for SFC did not influence [P > . 10] ADG but tended [P > . 10] to increase DMI/gain and decreased [P < .05] the NE(m) and NE(g) of the diet by 3.4 and 4.3%, respectively. Ruminal OM digestion was similar (P > .10] for SFC and SFW. Flow of microbial N to the small intestine was 12% greater [P < .05] with SFW. Total tract digestibilities of OM and starch were similar [P > .10] for both grains. However, ADF digestion was lower [34%, P < .01] with SFW. It is concluded that the feeding value of supplemental fat is similar for wheat- and corn-based finishing diets. The performance response to supplemental YG and COS was similar. The NE(m) and NE(g) values of YG were 6.35 and 4.93 Mcal/kg, respectively, whereas the corresponding values for COS were 5.69 and 4.60 Mcal/kg. Supplementation of growing-finishing diets with up to 6 % [.45 kilograms/day] of fat did not directly influence body composition. The NE value of SFW was approximately 96% of the value of SFC.