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Relationships between fiber contents and in vitro dry matter digestibility of alfalfa and grass silages.

C. Plett




Relationships between fiber contents and in vitro dry matter digestibility of alfalfa and grass silages.
C. Plett*1, A. Scott1, K. H. Ominski1, N. McLean2, C. Lafreniere3, S. Bittman4, J. C. Plaizier1. 1University of Manitoba Winnipeg, MB, Canada, 2Dalhousie University Truro, NS, Canada, 3Universit� du Qu�bec en Abitibi-Temiscamingue Rouyn-Noranda, QC, Canada, 4Agriculture and Agri-Food Canada Agassiz, BC, Canada.

To assess how the fiber contents of silages of perennial forages are related to their in vitro dry matter digestibility (IVTDMD), 270 samples of first cut alfalfa, grass, and alfalfa/grass silages were collected from dairy farms throughout Canada. Samples were analyzed for NDF and ADF by wet chemistry and for IVTDMD using 48 h incubation the ANKOM Daisy II system with an NDF ending. Summary statistics (Table 1) show that the ADF and NDF contents of the samples collected had a wide range in composition and were representative of first-cut alfalfa and alfalfa/grass silages (NRC, 2001. National Research Council, 2001 Nutrient Requirements of Dairy Cows). Pearson correlations between the ADF, NDF, and IVTDMD contents of the samples were determined using the SAS software, as the NDF and ADF contents of forages are routinely used to determine feed intake, energy content and digestibility of ruminant feeds. The correlation coefficients of the regression of ADF on IVTDMD and of NDF on IVTDMD, were −0.41 (P < 0.01) and −0.55 (P < 0.01), respectively. A reason for the low correlation coefficients may be that a NDF ending, rather than a pepsin ending for the Daisy II method was used, as the former method results in higher dry matter digestibility estimates. Differences in the alfalfa to grass ratio among samples may also have contributed to the low correlations. Our data does not indicate how the IVTDMD data can best be used for quality assessment and diet formulation when AFD and NDF analyses are available. More research may also be needed to modify the Daisy II method to provide more accurate estimate of total-tract dry matter digestibility in cattle.Table 1.

ItemMinimum25th percentileMedian75th percentileMaximum
NDF, % DM34.142.246.350.964.4
ADF, % DM24.030.132.836.049.3
IVTDMD, %45.358.763.468.578.7

Keywords: fiber, in vitro dry matter digestibility, silages.