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Effects of Different Inoculum Used for in vitro and in situ Digestion Procedures Performed on Corn Residue Samples
Neutral detergent fiber digestibility (NDF digestibility) is an important assay in determining the energy content of forage. In vitro and in situ procedures are traditionally carried out using an inoculum retrieved from a donor on a 30% concentrate diet. However, the diet fed to the donor may impact NDF digestibility estimates. Therefore, a study was conducted to assess the effects of donor diets on in vitro and in situ NDF digestibility. Four ruminally canulated steers were utilized to compare 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% Sweet Bran was fed to the remaining two steers. Residue samples consisting of 2-row, 4-row, 6-row, 8-row, conventional bale, leaf, husk, stalk and cob, along with five grass hays, were evaluated in situ and in vitro using inoculant from both sets of steers. All samples were tested with each inoculum from each individual steer, to test for an interaction of inoculum and sample type. This process was repeated in three runs, and steer inoculum source within run was the experimental unit (n = 6). The NDF digestibility of the corn residue was also determined utilizing in situ rumen incubation. No 3-way interaction was observed, in vitro or in situ, for time by sample by diet (P = 0.99). There were no interactions for time by sample (P = 0.79) or diet by sample (P = 0.99) in vitro. There was a tendency for an interaction for diet by time (P = 0.11) where diet significantly (P = 0.03) affected NDF digestibility at 48 h, but not at 24 h. There was an effect (P < 0.01) for diet in situ. That is, average NDF digestibility was consistently greater for both residue and grass samples when the donor was fed a high corn residue diet. At 28 and 48 hours, in situ, diet impacted NDF digestibility (P < 0.01). However, there was no effect of diet, in situ, fed to donor at 36 hours (P = 0.45). This study shows that the diet of the donor animal does affect NDF digestibility estimates of corn residue samples. Therefore, when trying to assess energy values using these techniques a set of standards with established in vivo digestibility values should be used for adjustment.
Keywords: corn residue, in situ, in vitro, neutral detergent fiber digestibility