CASE STUDY: In situ determination of protein digestibility of dried distillers grains containing 3 lipid concentrations using a mobile bag method

Ethanol producers remove lipid from distillers grains (DG) for applications such as biodiesel production. The effects of the lipid removal on ruminal protein degradability and total-tract CP digestibility of DG are not known. Five ruminally and duodenally cannulated Angus-cross steers (BW = 434 ± 15 kg) were used to incubate in situ bags for determination of protein digestibility of low-lipid (5.54%) DG, medium-lipid (8.40%) DG, high-lipid (12.46%) DG, and cottonseed meal. Ingredients were weighed into individual in situ bags and incubated in the ventral sac of the rumen for 16 h. After ruminal incubation and simulated abomasal digestion, bags were inserted into the duodenal cannula of corresponding steers and collected from feces approximately 12 to18 h later. Bags were washed, dried, and analyzed for CP. The CP concentration in DG increased with decreasing lipid concentrations, and the RUP fraction of the CP in DG decreased with decreasing lipid concentration (54.5, 54.8, and 60.1 ± 1.8% RUP for low-, medium-, and high-lipid DG, respectively) suggesting that lipid extraction increased rumen protein degradability. The total-tract indigestible protein and postruminal digestibility of RUP were not different among the varying lipid concentrations in DG. The RUP digestibility of the low-, medium-, and high-lipid DG (79.5, 80.4, and 80.6 ± 2.0%, respectively) was consistent with the commonly used NRC model value of 80%. These data suggest the extraction of lipid from DG may alter ruminal degradability of CP but does not change the postruminal digestibility of the RUP.