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Currently use fiber to estimate energy |
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relationship not adequate for high producing
herds |
|
relationship varies with level of intake |
|
|
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No estimate of bypass protein |
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Empirical equations |
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Summative equations |
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Rumen digestion kinetics |
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|
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simple linear regression equations |
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regressor: chemical constituent (ADF, NDF) |
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|
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easy to measure |
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negatively correlated with digestibility |
|
population specific |
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poor sensitivity |
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|
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partition of feeds into fractions of similar
nutritive characteristics (cell wall, cell contents) |
|
cell contents (CP, NFC, Fat) ... 98%
digestibility |
|
cell wall (NDF) ... variable digestibility |
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endogenous excretions (MFE) |
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TDN: (Sum of digestible NDF, CP, NFC, Fat) - MFE |
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|
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based on cause-effect relationships |
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sensitive to changes in nutrient concentration |
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not population specific |
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excessive number of assays |
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need to measure lignin |
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static model |
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no rates of digestion or passage |
|
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|
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reproducing the reactions or environment
occurring in the rumen |
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in situ -- in vitro |
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rumen disappearance: digestion + passage |
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rate of passage intake production
level |
|
|
|
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more accurate and precise predictor of in vivo digestibility |
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direct measurement of the rate and extent of
forage digestion in animals at different intakes |
|
not practical for commercial forage testing
laboratories (cost, time...) |
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|
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Predictions of digestibility by the empirical
and in situ digestion kinetic approaches were not consistent (low
correlations) |
|
|
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NIRS showed potential to accurately predict
rumen digestion kinetics |
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as good as chemical values |
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A, C, ISDMD very accurate |
|
B and kd lower accuracy and affected
by particle size |
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Animals: 12 lactating dairy cows (6 cannulated) |
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Experimental design: 3x3 Latin square |
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Treatments:
L-ADF1 L-ADF2
H-ADF (58:42) |
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Measurements: |
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digestibility, intake, rate of passage |
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milk production and composition |
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rumen physical and chemical characteristics |
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Validation statistics of in vitro-NIR equations: |
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equations for A, C, IVDMD are accurate |
|
equations for B, kd lack accuracy (by
NIRS) |
|
all parameters were biased |
|
slopes showed that trends were consistent with in
vitro |
|
|
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Both empirical and in vitro-NIR equations are
correlated with in vitro digestibility |
|
Better results with in vitro-NIR equations |
|
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|
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Better determine RUP of feedstuffs |
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Avoid overfeeding protein |
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Balance rations more cost effectively |
|
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Determine if soybean roasting adequate |
|
|
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Pattern of rumen degradation determined over
time |
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Each sample digested in 8 milking cows |
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Digestion for 24 hours |
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Residue corrected for microbial protein |
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Results predicted by NIR |
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Notes