Comparison of techniques and grinding size to estimate digestibility of forage based ruminant diets

We compared prediction of in vivo dry matter (DMD) and neutral detergent fiber (aNDFD) digestibility by the following techniques: (1) Tilley and Terry two-stage in vitro (conventional in vitro or IVDMD), (2) DaisyII in vitro (DaisyII), and (3) filter bag in situ preceded by 48 h acid–pepsin treatment. In addition, we also evaluated the effects due to sample size (0.25 g versus 0.50 g) and Wiley Mill grinding size (1-mm versus 2-mm screens). In Experiment 1, fifteen forage species from mixedconifer rangelands were used to evaluate digestion estimation techniques. Compared to IVDMD, DaisyII and in situ techniques overestimated (P<0.01) DMD. In Experiment 2, we used meadow hay samples to compare the above techniques to in vivo DMD. In situ DMD, DaisyII DMD, and IVDMD were greater (P<0.01) than in vivo DMD. In contrast, in situ aNDFD did not differ (P=0.13) from in vivo aNDFD for sheep. In Experiment 3, we used grasses, forbs, shrubs, and lichen in separate analyses to evaluate the interaction of Wiley Mill grind size (1-mm versus2-mm) and digestibility technique. For grass hay, DaisyII and in situ DMD were increased (P<0.05), and IVDMD was decreased (P<0.05), compared to in vivo DMD. DaisyII and in situ aNDFD decreased (P<0.05), compared to Abbreviations: ADF, acid detergent fiber; BW, body weight; CP, crude protein; CV, coefficient of variation; DM, dry matter; DMD, dry matter digestibility; GLM, general linear model; IVDMD, in vitro dry matter digestibility; MWU, modified wohlgemuth unit; aNDF, neutral detergent fiber assayed with a heat stable alpha amylase and expressed inclusive of residual ash; aNDFD, aNDF digestibility; SAS, statistical analysis system; S.E.M., pooled standard error of the least squares means ∗ Corresponding author. Tel.: +1 541 562 5129; fax: +1 541 562 5348. E-mail address: [email protected] (T. DelCurto). 0377-8401/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2007.04.007 #591