Effect of Isolated Nutrient Components of Modified Distillers Grains Plus Solubles on Digestibility and Digestible Energy in Growing Diets

Byproducts are a good source of protein and energy in ruminant diets and replacing corn with distillers grains (DG) has led to improvements in cattle performance. Objectives of this study were to evaluate the contribution of nutrient components of DG on diet digestibility, digestible energy (DE), and in situ NDF disappearance in high forage diets fed to steers. An 84 d digestion study was conducted utilizing 6 ruminally fistulated steers (initial BW = 362 kg, SD = 27 kg) in a Latin square design dosed daily with 10 g of TiO₂. Diets contained 56.0% diet DM brome and 40% concentrate. The control diet contained 40% diet DM dry-rolled corn (CON) while the DG diet contained 40% modified distillers grains plus solubles (MDGS). The remaining four diets replaced a portion of DRC and included byproducts selected to isolate the various nutrient components found in MDGS: corn bran included at 20% of diet DM to represent the fiber found in MDGS (FIB), corn gluten meal included at 20% of diet DM to represent the protein in MDGS (CGM), tallow included at 3% of diet DM to represent the fat in MDGS (TAL), and solubles (SOL) included at 15% of diet DM to represent the solubles found in MDGS. Six periods 14 d in length allowed 8 d for diet adaptation at ad libitum intake. Starting on d 9 steers were fed 95% ad libitum intake with fecal grab samples collected at 0700, 1100, 1500, and 1900 h on d 11 to d 14. Digestible energy was measured utilizing bomb calorimetry. Fiber (brome and corn bran) was ruminally incubated (24 h on d 14) to determine NDF disappearance. No differences in DM intake or OM intake were observed among diets (P ≥ 0.70). Neutral detergent fiber intake (NDFI) was greatest for diets FIB or MDGS (P < 0.01). No differences in DM digestibility, OM digestibility, or NDF digestibility were observed (P ≥ 0.19). Replacement of DRC by MDGS and CGM resulted in the greatest DE (3.1 Mcal / g and 3.0 Mcal / g, respectively; P < 0.01) compared to all other diets. Lowest DE was observed in the CON and SOL diets (3.85 and 3.86 Mcal / g, respectively). Treatment had no effect on in situ NDF disappearance (P ≥ 0.12). Overall it was observed that protein is the component of MDGS that results in increased DE in high forage diets.