In Vitro Apparent Ruminal Digestibility of Diets Containing Corn Distillers Grain with Different Quantities of Crude Fat

Four dual-flow continuous fermenters were used in a Latin square design to determine the apparent ruminal digestibility and ruminal characteristics of diets containing dried distillers grains plus solubles (DDGS) at different levels of fat content. Fermenters were randomly assigned to one of the following treatments: 1) 40% DDGS containing 4.82% fat content (40 LOW); 2) 40% DDGS plus corn oil to obtain 7.5% fat (40 MED); 3) 40% DDGS plus corn oil to obtain 10.5% fat (40 HIGH); or 4) 70% DDGS plus corn oil to obtain 7.5% fat (70 MED). Rumen fluid was collected at the beginning of each period from two ruminally cannulated Angus cows previously adapted to diets containing DDGS. Each period consisted of 10 days with a seven day adaptation period followed by three days of sample collection. Calories per gram of diet increased as percent fat increased and calories per gram was greater at the 70% inclusion of DDGS compared to 40% inclusion of DDGS at all levels of fat content. However, level of fat in the diet did not affect (P ≥ 0.35) apparent ruminal digestibility of DM, NDF, ADF, CP or total calories. Similarly, inclusion rate of DDGS had no effect (P ≥ 0.35) on nutrient digestibility. Ammonia concentrations were greatest (P = 0.0002) for 70 MED compared to the other treatments. However, treatment had no effect (P ≥ 0.16) on volatile fatty acid production with the exception of propionate which increased (P =0.05) as the level of DDGS increased from 40 to 70% inclusion rate. This data would suggest that level of fat content of DDGS has no negative effects on apparent ruminal digestibility and selected ruminal characteristics. From an economic perspective, higher fat DDGS should have a higher price differential, but lower fat DDGS can still be an effective protein and energy substitute.