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Effects of roughage source and distillers grain concentration on beef cattle finishing performance, carcass characteristics, and in vitro fermentation

Abstract:

Two experiments were conducted toevaluate the effects of wet distillers grains plus solubles(DG) and roughage source on finishing cattle performance,carcass characteristics, and in vitro fermentation.In Exp. 1, crossbred beef steers (n = 224, initialBW = 349 kg) were used in a randomized completeblock design with a 2 × 3 + 1 factorial arrangement oftreatments. Experimental diets were a standard steamflakedcorn (SFC)-based control (no DG and 10% alfalfahay), and either 15 or 30% DG (DM basis) withroughage sources of alfalfa hay (15-AH and 30-AH),Coastal bermudagrass hay (15-BG and 30-BG), or sorghumsilage (15-SS and 30-SS). Within each DG concentration,roughages provided an equivalent percentageof NDF to 7.5% AH. Steers consuming 15% DGhad greater (P < 0.04) final BW, ADG, and G:F thanthose fed 30% DG. Feeding AH as the roughage sourcewith DG resulted in decreased final shrunk BW andADG (P < 0.02) compared with BG and SS. FeedingSS as the roughage source decreased (P = 0.01) G:Frelative to BG. Hot carcass weight was greater (P <0.01) for steers consuming 15 vs. 30% DG, tended tobe least for diets with AH as the roughage source (P= 0.06), and did not differ for the control vs. the otherdiets (P = 0.86). Control cattle had an increased (P =0.05) proportion of USDA Choice or greater carcassescompared with the average of the other treatments. InExp. 2, the same 2 × 3 +1 factorial arrangement asin Exp. 1 was used to examine the effects of roughagesource and DG on IVDMD, culture fluid osmolality,and gas production kinetics. In vitro DMD tended (P <0.09) to be greater for BG compared with SS at 6 and36 h of incubation and was greater for AH vs. the meanof BG and SS at 18 h (P = 0.01). Culture fluid osmolality,asymptotic maximal gas production, fractionalrate of gas production, and lag time of gas productiondid not differ among treatments (P > 0.14). Overall,feeding 15% DG in SFC-based diets increased ADG,BW, and HCW relative to 30% DG. In addition, feedingAH tended to decrease ADG, final BW, and HCWrelative to the other 2 roughage sources, whereas BGimproved G:F over SS. These data suggest that includingthe smaller amount of DG and BG as the roughagesource resulted in improved performance relativeto other combinations, and that substituting roughageson the basis of equivalent NDF concentration might notbe ideal for optimizing performance when feeding SFCbasedfinishing diets that contain DG. © American Society of Animal Science. All rights reserved.