situ digestibility when compared to a 30% concentrate diet. Procedure Four ruminally canulated steers were utilized in this study comparing two forage diets. A mixed diet consisting of 70% brome and 30% dry distillers grains (DDGS) was fed to two steers and a high corn residue diet with 70% stalks and 30% One of the most important feed assays to assess the energy of forages is the neutral detergent fi ber digestibility (NDF digestibility). In vitro and in situ procedures are traditionally

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... d out using an inoculum retrieved from a donor on a 30% concentrate diet to evaluate feed. However, the diet fed to the donor may impact NDF digestibility estimates. Th erefore, the objective of this study was to evaluate the eff ects of diff erent donor diets on in vitro and in Summary An in vitro and in situ study was conducted to assess the eff ects of donor diet at time of incubation on NDF digestibility of corn residue samples. Residue samples had greater NDF digestibility when animals were on a similar diet (i.e. a high corn residue diet). Digestibility of NDF was greater when time of incubation increased. Th e diet of the donor steer had greater impact as time of incubation increased implying that the animal's diet, and incubation time, has an impact on the true values of NDF digestibility.